United States Office of Water EPA-821-R-01-034
Environmental Protection 4303
Agency
v/EPA Method 1605: Aeromonas in Finished
Water by Membrane Filtration using
Ampicillin-Dextrin Agar with
Vancomycin (ADA-V)
October 2001
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Acknowledgments
This method was prepared under the direction of Mary Ann Feige of the Office of Ground Water and
Drinking Water's Technical Support Center within the U.S. Environmental Protection Agency's (EPA's)
Office of Water (OW). This document was prepared under an EPA Engineering and Analysis Division
contract by DynCorp Information & Enterprise Technology, Inc.
The contributions of the following persons and organizations to the development of this method are
gratefully acknowledged:
Boutros, Susan, and John Chandler, Environmental Associates Ltd., 24 Oakbrook Dr., Ithaca, NY, 14850
Danielson, Richard, BioVir Laboratory, 685 Stone Road Unit # 6, Benicia, CA 94510
DeLuca, Neil, New York City DEP-Sutton Park, 19 West Lake Drive, Valhalla, NY 10595
Fallen, Kristen, Analytical Services Incorporated, 130 Allen Brook Lane, Williston, VT 05495
Fukuoka, John, MWH Laboratories, 555 East Walnut St., Pasadena, CA 91101-1658
Hall, Nancy, Cathy Lord, and Nelson Moyer, University of Iowa, Oakdale Hall, Iowa City, IA 52242
Hamblin, Richard and Jason Burlage, Oak Ridge Institute for Science and Education, 26 West Martin
Luther King Dr., Cincinnati, OH 45268-1320
Hunt, Margo, U.S. EPA, Office of Environmental Information, Quality Staff (2811R), 1200 Pennsylvania
Ave. NW, Washington, DC 20460
Johnson, Steve L., Missouri American Water Company-St. Louis, 901 Hog Hollow Rd., St. Louis, MO
63017
Kitchen, Terry, City of Phoenix Water Services Laboratory, 2474 South 22nd Ave., Phoenix, AZ 85009
Kluender, Sharon, Wisconsin State Laboratory of Hygiene, 2601 Agriculture Dr., Madison, WI
53718
Pope, Misty, Kevin Connell, Jessica Pulz, Ken Miller, Kyle May, Jason Kempton, and Ben Meadows,
DynCorp Information and Enterprise Technologies, 6101 Stevenson Avenue, Alexandria, VA
22304
Rodgers, Mark, U.S. EPA Office of Research and Development, National Exposure Research Laboratory,
26 West Martin Luther King Dr., Cincinnati, OH 45268-1320
Roefer, Peggy, Maria Johnson, and Darlene Jones, Southern Nevada Water System, 243 Lakeshore Rd.,
Boulder City, NV 89005
Schreppel, Connie, Upper Mohawk Regional Water Board, 1 Kennedy Plaza, Utica, NY 13502
Shadix, Lois, and Bonita Newport, U.S. EPA Office of Water, Office of Ground Water and Drinking
Water, Technical Support Center, 26 West Martin Luther King Dr., Cincinnati, OH 45268-1320
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Singh, Ajaib and Clem Ng, Milwaukee Health Department Laboratories, 841 N. Broadway, Room 205,
Milwaukee, WI 53202
Smallwood, Wayne, National Council of Aging; Senior Environmental Employment Program 26 West
Martin Luther King Dr., Cincinnati, OH 45268-1320
Smith, James and Mike Herzog, Montana Microbiological, 2010 N. 7th Ave., Bozeman, MT 59715
Wingfield, David, Florida DEP, 3952 W. Martin Luther King Blvd, Tampa, FL 33614
Wong, Rebecca and Fu-Chih Hsu, Environmental Health Laboratories, 110 South Hill Street, South
Bend, IN 46617
Yanko, William, Private Consultant, 1111 El Sur Ave, Arcadia, CA 91006
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Disclaimer
This method has been validated by the U.S. Environmental Protection Agency through an interlaboratory
validation study, and will be proposed for use in drinking water monitoring in the Federal Register. This
method is not an EPA-approved method until it is promulgated as an approved method in the Federal
Register.
Mention of trade names or commercial products does not constitute endorsement or recommendation for
use.
IV
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Introduction
Aeromonas is a common genus of bacteria indigenous to surface waters, and may be found in non-
chlorinated or low-flow parts of chlorinated water distribution systems. Monitoring their presence in
distribution systems is desirable because some aeromonads may be pathogenic and pose a potential
human health risk. Method 1605 describes a membrane filtration technique for the detection and
enumeration of Aeromonas species. This method uses a selective medium that partially inhibits the
growth of non-target bacterial species while allowing most species of Aeromonas to grow. Aeromonas is
presumptively identified by the production of acid from dextrin fermentation and the presence of yellow
colonies on ampicillin-dextrin agar medium with vancomycin (ADA-V). Yellow colonies are counted and
confirmed by testing for the presence of cytochrome c (oxidase test), and the ability to ferment trehalose,
and produce indole.
Laboratories are not permitted to modify ADA-V media or procedures associated with filtration (Sections
10.1 through 10.10). However, the laboratory is permitted to modify method procedures related to the
confirmation of colonies (Section 10.11) to improve performance or lower the costs of measurements
provided that 1) presumptively identified yellow colonies submitted to confirmation are tested for the
presence of cytochrome c (oxidase test), and the ability to ferment trehalose, and the ability produce
indole, and 2) all quality control (QC) tests cited in Section 9.2.12 are performed acceptably and QC
acceptance criteria are met. For example, laboratories may prefer to streak colonies that are submitted to
confirmation on tryptic soy agar (TSA), instead of nutrient agar. The laboratory may not omit any quality
control analyses.
This method is for use in the Environmental Protection Agency's (EPA's) data gathering and monitoring
programs under the Safe Drinking Water Act.
Questions concerning this method or its application should be addressed to:
Mary Ann Feige
U.S. EPA Office of Water
Office of Ground Water and Drinking Water
Technical Support Center
26 West Martin Luther King Drive
Cincinnati, OH 45268-1320
Requests for additional copies of this publication should be directed to:
Water Resource Center
Mail Code RC-4100
401 M Street, SW
Washington, D.C. 20460
(202) 260-7786 or (202) 260-2814
VI
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Table of Contents
1.0 Scope and Application 1
2.0 Summary of Method 1
3.0 Definitions 2
4.0 Interferences and Contamination 2
5.0 Safety 2
6.0 Equipment and Supplies 3
7.0 Reagents and Standards 4
8.0 Sample Collection, Preservation, and Storage 7
9.0 Quality Control 8
10.0 Procedure 16
11.0 Data Analysis and Calculations 18
12.0 Method Performance 20
13.0 Pollution Prevention 20
14.0 Waste Management 20
15.0 References 21
16.0 Tables and Flowcharts 22
17.0 Glossary 25
vm
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Method 1605: Aeromonas in Finished Water by Membrane Filtration
using Ampicillin-Dextrin Agarwith Vancomycin (ADA-V)
October 2001
1.0 Scope and Application
1.1 This method describes a membrane filter (MF) procedure for the detection and enumeration of
Aeromonas species in finished water samples. Aeromonas is a common genus of bacteria
indigenous to surface waters. Its numbers are more likely to be greater during periods of warmer
weather and when increased concentrations of organic nutrients are present. It is also more likely
to be found in non-chlorinated water distribution systems or low-flow parts of chlorinated
systems. Some Aeromonas species are opportunistic pathogens.
1.2 This method is adapted from Havelaar et al. (1987) for the enumeration of Aeromonas species in
finished water by membrane filtration (Reference 15.1). It is a quantitative assay that uses a
selective medium which partially inhibits the growth of non-target bacterial species while
allowing Aeromonas to grow. Aeromonas is presumptively identified by the production of acid
from dextrin fermentation producing yellow colonies. Presumptively positive colonies are
counted and confirmed by testing for the presence of cytochrome c (oxidase test), and the ability
to ferment trehalose, and produce indole.
1.3 This method is designed to meet the finished water monitoring requirements of the U.S.
Environmental Protection Agency. Aeromonas was included on the Contaminant Candidate List
(CCL) (Mar. 2, 1998, 63 FR 10274) and in the Revisions to the Unregulated Contaminant
Monitoring Proposed Rule (UCMR) (September 17, 1999, 64 FR 50556). Contaminants listed in
the UCMR are candidates for future regulation and may be included in a monitoring program for
unregulated contaminants. Unregulated contaminant monitoring would be required for large
systems and a representative sample of small and medium sized water distribution systems.
1.4 This method was subjected to an interlaboratory validation study involving 11 laboratories and 11
finished drinking water matrices. This method was not validated for other water types. Use of
this method and appropriate validation for other water types is the responsibility of the user.
2.0 Summary of Method
2.1 The method provides a direct count of Aeromonas species in water based on the growth of yellow
colonies on the surface of the membrane filter using a selective medium. A water sample is
filtered through 0.45-jwm-pore-size membrane filter. The filter is placed on ampicillin-dextrin
agar with vancomycin (ADA-V) and incubated at 35°C ± 0.5 °C for 24 ± 2 hours. This medium
uses ampicillin and vancomycin to inhibit non-Aeromonas species, while allowing most
Aeromonas species to grow. The medium uses dextrin as a fermentable carbohydrate, and
bromothymol blue as an indicator of acidity produced by the fermentation of dextrin.
Presumptively identified yellow colonies are counted and confirmed by testing for the presence of
cytochrome c (oxidase test), and the ability to ferment trehalose and produce indole.
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Method 1605 - Aeromonas
2.2 The membrane filtration procedure provides a direct count of culturable Aeromonas in water
samples that is based on the growth of bacterial colonies on the surface of the membrane filter
placed on a selective medium.
2.3 Aeromonas isolates may be archived for further analysis to determine species or hybridization
group by inoculating a nutrient agar slant for short term use or shipping, or nutrient broth for
freezing.
3.0 Definitions
3.1 Aeromonas are bacteria that are facultative anaerobes, Gram-negative, oxidase-positive, polarly
flagellated, and rod shaped. They are classified as members of the family Aeromonadaceae.
Demarta et al. (1999) reported 15 Aeromonas species based on 16S rDNA sequences though not
all are officially recognized. Some species have been associated with human disease. In this
method, Aeromonas are those bacteria that grow on ampicillin-dextrin agar with vancomycin
(ADA-V), produce yellow colonies, are oxidase-positive, and have the ability to ferment
trehalose and produce indole.
3.2 Definitions for other terms are provided in the glossary at the end of the method (Section 17.3).
4.0 Interferences and Contamination
4.1 Water samples containing colloidal or suspended particulate material may clog the membrane
filter and prevent filtration or cause spreading of bacterial colonies which could interfere with
identification of target colonies.
4.2 Other ampicillin/vancomycin resistant bacteria that are not aeromonads may be able to grow on
this medium. Some of these bacteria may also produce yellow colonies if they are able to produce
acid byproducts from the fermentation of dextrin or some other media component, or if they
produce a yellow pigment. Enterococcus are reported to produce pinpoint-size yellow colonies on
ADA. Confirmation of presumptive Aeromonas colonies is necessary to mitigate false positives.
5.0 Safety
5.1 Some strains of Aeromonas are opportunistic pathogens. Sample containers and waste materials
should be autoclaved prior to cleaning or disposal.
5.2 The analyst/technician must know and observe the normal safety procedures required in a
microbiology laboratory while preparing, using, and disposing of cultures, reagents, and other
materials.
5.3 This method does not address all safety issues associated with its use. The laboratory is
responsible for maintaining a safe work environment and a current awareness file of OSHA
regulations regarding the safe handling of the chemicals specified in this method. A reference file
October 2001
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Method 1605 - Aeromonas
of material safety data sheets (MSDSs) should be available to all personnel involved in these
analyses.
6.0 Equipment and Supplies
Note: Brand names, suppliers, and part numbers are for illustrative purposes only. No endorsement is
implied. Equivalent performance may be achieved using apparatus and materials other than
those specified here, but demonstration of equivalent performance that meets the requirements of
this method is the responsibility of the laboratory.
6.1 Equipment for collection and transport of samples to laboratory
6.1.1 Autoclavable sample container—Use sterile, non-toxic, glass or plastic containers with
a leak-proof lid. Ensure that the sample container is capable of holding a 1-L sample
with ample headspace to facilitate mixing of sample by shaking prior to analysis.
6.1.2 Ice chest
6.1.3 Icepacks
6.2 Autoclavable dilution bottles—125-mL marked at 99 mL or 90 mL; commercially produced
dilution bottles may be used
6.3 Rinse water bottles
6.4 Sterile plastic or autoclavable glass pipettes with a 2.5% tolerance—To deliver (TD), 1- and
10-mL
6.5 Pipette bulbs or automatic pipetter
6.6 Autoclavable pipette container (if using glass pipettes)
6.7 Thermometer—with 0.5 °C gradations checked against a National Institute of Standards and
Technology (NIST) certified thermometer, or one that meets the requirements of NIST
Monograph SP 250-23
6.8 Inoculating loop—Sterile metal, plastic, or wooden applicator sticks
6.9 Burner—Flame or electric incinerator for sterilizing metal inoculating loops and forceps
6.10 Colony counting device—Mechanical, electric or hand tally
6.11 Hotplate stirrer
6.12 Magnetic stir bar
6.13 Graduated cylinders—100 mL, 500 mL and 1 L, sterile, polypropylene or glass
6.14 Balance—Capable of weighing samples up to 200 g, with a readability of 0.1 g
6.15 Weigh boats
6.16 pH meter
6.17 Turbidimeter (optional)
6.18 Equipment for membrane filter procedure
October 2001
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Method 1605 - Aeromonas
6.18.1 Incubator—Hot air or water-jacketed microbiological type to maintain a temperature of
35°C±0.5°C
6.18.2 Petri dishes—sterile, 50x9 mm or other appropriate size
6.18.3 Membrane filtration units (filter base and funnel made of glass, plastic, or stainless
steel), wrapped with aluminum foil or Kraft paper, and sterilized by autoclaving.
6.18.4 Vacuum source
6.18.5 Flasks—1-L vacuum filter with appropriate tubing; a filter manifold to hold a number
of units is optional
6.18.6 Side-arm flask to place between vacuum source and filtration devices or filter manifold
6.18.7 Membrane filters—Sterile, cellulose ester, white, gridded, 47-mm-diameter with
0.45-pm pore size (German E04WG04700 or equivalent)
6.18.8 Forceps—Sterile, straight or curved, with smooth tips to handle filters without causing
damage
6.18.9 Ethanol or other alcohol in a container to sterilize forceps
6.18.10 Testtubes—125 x 16mm sterile, screw-cap tube
6.19 Dissecting microscope—Low power (10X to 15X), binocular, illuminated
6.20 Autoclave—Capable of 121 °C at 15 psi. Must meet requirements set forth in the Manual for the
Certification of Laboratories Analyzing Drinking Water, 4th Edition. (Reference 15.5)
6.21 Membrane filters (for sterilization purposes)—Sterile with 0.22-jwm pore size (Gelman Acrodisc
No. 4192 or equivalent)
7.0 Reagents and Standards
7.1 Purity of reagents and culture media—Reagent-grade chemicals shall be used in all tests. Unless
otherwise indicated, reagents and culture media shall conform to the specifications in Standard
Methods for the Examination of Water and Wastewater (latest edition approved by EPA in 40
CFRPart 141), Section 9050 (Reference 15.2). The agar used in preparation of culture media
must be of microbiological grade.
7.2 Purity of water—Reagent-grade water conforming to specifications in Manual for the
Certification of Laboratories Analyzing Drinking Water, 4th Edition (Reference 15.5) or Standard
Methods for the Examination of Water and Wastewater (latest edition approved by EPA in 40
CFRPart 141), Section 9020 (Reference 15.2).
7.3 Phosphate buffered dilution water
7.3.1 Concentrated stock phosphate buffer solution—Dissolve 34.0 g potassium dihydrogen
phosphate (KH2PO4) in 500 mL reagent-grade water. Adjust the pH to 7.2 ± 0.5 with
IN sodium hydroxide (NaOH) and dilute to 1 L with reagent-grade water. Autoclave or
filter sterilize through a filter with 0.22-jwm-pore-size.
7.3.2 Magnesium chloride solution—Dissolve 81.1 g magnesium chloride hexahydrate
(MgCl2 6H20) in reagent-grade water and dilute to 1 L. Autoclave or filter sterilize
through a 0.22-//m-pore-size filter.
7.3.3 Prepare phosphate buffered dilution water by adding 1.25 mL of concentrated stock
phosphate buffer solution (Section 7.3.1) and 5.0 mL of magnesium chloride solution
October 2001
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Method 1605 - Aeromonas
(Section 7.3.2) to a 1-L graduated cylinder and adjust final volume to 1 L with
reagent-grade water. Prepare a portion of buffered dilution water in 1-L bottles for rinse
water. Autoclave or filter sterilize through a filter with 0.22-ywm-pore-size.
7.3.4 Stored phosphate buffered dilution water should be free from turbidity.
7.4 Ampicillin-dextrin agar with vancomycin (ADA-V)
7.4.1 Preparation of dextrin agar—EPA highly recommends the use of commercial ADA (m-
Aeromonas Selective Agar Base [Havelaar]), Section 7.4.1.1. However, ADA may be
prepared by the laboratory (Section 7.4.1.2 )
7.4.1.1 Commercial dextrin agar—Tech Pac (distributor, tech@fuse.net).
Cincinnati, Ohio; Biolife (www.biolifeit.com) Italiana Sri, 272 Viale
Monza, Milan, Italy, Cat. No. 401019 or equivalent. Prepare 1-L of media,
according to manufacturer's instructions. Cool to room temperature, and
adjust pH to 8.0 using IN NaOH or IN HC1. Autoclave for 15 min, cool to
50°C.
7.4.1.2 Laboratory-prepared dextrin agar.
7.4.1.2.1 5.0 g tryptose—Difco cat. no. 0124-17, or equivalent
7.4.1.2.2 11.4 g dextrin—Difco cat. no. 0161-17, or equivalent
7.4.1.2.3 2.0 g yeast extract—Difco cat. no. 0127-17, or equivalent
7.4.1.2.4 3.0 g sodium chloride (NaCl)—Baker cat. no. 3624, or
equivalent
7.4.1.2.5 2.0 g potassium chloride (KC1)—Fisher cat. no. P217-500, or
equivalent
7.4.1.2.6 0.1 g magnesium sulfate heptahydrate (MgSO47H2O)—Fisher
cat. no. M63-500, or equivalent
7.4.1.2.7 0.06 g ferric chloride hexahydrate (FeCl3 6H2O)—Sigma cat.
no. F-2877, or equivalent
7.4.1.2.8 0.08 g bromothymol blue—Baker cat. no. D470, or equivalent
7.4.1.2.9 Sodium deoxycholate—Sigma cat. no. D-6750, or equivalent.
Add 100 mg of sodium deoxycholate to 10 mL of reagent
water.
7.4.1.2.10 13.0 g agar, bacteriological grade—Fisher cat. no. BP1423-
500, or equivalent.
7.4.1.2.11 Add reagents in Sections 7.4.1.2.1 through 7.4.1.2.8 to 1-L of
reagent-grade water, stir to dissolve and adjust pH to 8.0 using
IN NaOH or IN HC1. After the pH has been adjusted, add
sodium deoxycholate (Section 7.4.1.2.9) and agar (Section
7.4.1.2.10) and heat to dissolve. Autoclave for 15 min, cool to
50°C.
7.4.2 Ampicillin, sodium salt—Sigma cat. no. A0166, or equivalent. Add 10 mg of
ampicillin, sodium salt to 10 mL reagent water. Prepare on the same day that medium is
prepared and filter sterilize through a 0.22-^m-pore-size filter. Alternatively, use
Biolife cat. no. 4240012 prepared according to manufacturer's instructions, taking care
to use an appropriate amount of ampicillin for the volume of media being prepared (for
example, use two vials for a 1-L batch of ADA-V). Follow manufacturer's instructions
October 2001
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Method 1605 - Aeromonas
for appropriate storage temperature and shelf-life. Wear suitable protective clothing,
gloves, and eye/face protection and prepare stock solutions in a chemical fume hood.
7.4.3 Vancomycin hydrochloride—Sigma cat. no. V2002, or equivalent. Add 2 mg of
vancomycin hydrochloride to 10 mL of reagent water. Filter sterilize through a
0.22-pm-pore-size filter. Follow manufacturer's instructions for appropriate storage
temperature and time. Wear suitable protective clothing, gloves, and eye/face
protection and prepare stock solutions in a chemical fume hood.
7.4.4 After dextrin agar (Section 7.4.1) has been autoclaved and cooled to 50°C, add the
sterile ampicillin (Section 7.4.2) and sterile vancomycin hydrochloride solutions
(Section 7.4.3).
7.4.5 Add approximately 5 mL of ADA-V per 50x9 mm petri dish and allow to solidify.
For larger plates, adjust volume appropriately. ADA-V plates should be stored in a
tight fitting container (i.e. sealed plastic bag) at a temperature of 1 °C to 5 °C for no
longer than 14 days.
7.5 Pentahydrate ACS Reagent grade sodium thiosulfate—Fisher cat. no. S445-500, or equivalent.
Prepare a 3% stock solution by adding 3 g sodium thiosulfate to 100 mL reagent-grade water.
7.6 Disodium salt of ethylenediaminetetraacetic acid (EDTA)—Sigma cat. no. E 4884, or equivalent.
EDTA should only be added to samples if metals in water samples exceed 1.0 mg/L. To prepare
stock solution, add 12.4 g EDTA to 80 mL of reagent-grade water. Adjust pHto 8.0 using ION
NaOH. After the pH has been adjusted, bring the volume up to 100 mL with reagent-grade water.
7.7 Positive control culture—Aeromonas hydrophila ATCC #7966; obtained from the American
Type Culture Collection (ATCC, 10801 University Blvd, Manassas, VA, 20110-2209;
http://www.atcc.org).
7.8 Negative culture control—Negative culture controls serve two purposes: to ensure the
laboratories are familiar with the color and morphology of non-Aeromonas bacteria that may
grow on ADA-V and to ensure that confirmation test results are appropriate. E. coll (ATCC
#25922) is the negative culture control for oxidase, Pseudomonas aeruginosa (ATCC #27853) is
the negative culture control for trehalose fermentation, and Bacillus cereus (ATCC #11778) is the
negative culture control for indole.
7.9 Nutrient agar—Difco cat. no. 0001-17 or equivalent. Prepare according to manufacturers
instructions.
7.10 Oxidase reagents—Dry Slide BBL cat. no. 231746 or equivalent.
7.11 0.5% Trehalose confirmation reagent
7.11.1 Add 5 g trehalose (Sigma cat. no. TO 167, or equivalent) to 100 mL water and filter
sterilize solution through a filter with 0.22-jwm-pore-size.
7.11.2 Prepare 900 mL purple broth base (Difco cat. no. 0222-17, or equivalent) according to
manufacturer's instructions and autoclave.
7.11.3 Aseptically add 100 mL trehalose solution to the cooled 900 mL of purple broth base.
7.11.4 Dispense into 6 mL or larger size tubes and fill approximately half full. Store in
refrigerator.
October 2001
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Method 1605 - Aeromonas
Note: Alternatively, prepare purple broth base according to manufacturers instructions, add 5 g
trehalose per liter, and filter sterilize through a filter with 0.22-jUm-pore-size.
7.12 Tryptone broth—Oxoid cat. no. CM0087B, or equivalent. Alternatively, the laboratory may
prepare tryptone broth by adding 10 g of tryptone (Difco cat. no. 0123-17 or equivalent) and 5 g
of NaCl to 1 L of reagent water. Autoclave or filter sterilize through a filter with 0.22-pm-pore-
size.
7.13 Kovac's reagent—Biomeriuex cat. no. V7050, or equivalent
8.0 Sample Collection, Preservation, and Storage
8.1 Adherence to sample preservation procedures and holding time limits specified in Standard
Methods for the examination of Water and Wastewater (Reference 15.2) is critical to the
production of valid data. Sample results will be considered invalid if those conditions are not met.
8.2 Preparation of sample bottles and sample collection—Samples must be representative of the
drinking water distribution system. Water taps used for sampling should be free of aerators,
strainers, hose attachments, mixing type faucets, and purification devices. Cold water taps should
be used. The service line should be cleared before sampling by maintaining a steady water flow
for at least two minutes (until the water changes temperature).
8.2.1 Use sterile, non-toxic, glass or plastic container (Section 6.1.1) with a leak-proof lid.
Ensure that the sample container is capable of holding a 1-L sample with ample
headspace to facilitate mixing of sample by shaking prior to analysis. Sampling
procedures are described in detail in Standard Methods for the Examination of Water
and Wastewater, Section 9060 (Reference 15.2).
8.2.2 Add 1 mL of 3% sodium thiosulfate stock (Section 7.5) per L of sample to sample
bottles prior to autoclave sterilization. Alternatively, if using presterilized sample
bottles, sodium thiosulfate should be autoclaved for 15 minutes or filter sterilized
through a filter with 0.22-pm-pore-size before adding to the sample bottles.
8.2.3 If metals in the sample exceed 1.0 mg/L, add 3 mL of EDTA stock solution (Section
7.6) per L of sample to sample bottles prior to autoclave sterilization. If using
presterilized sample bottles, EDTA should be autoclaved for 15 minutes or filter
sterilized through a filter with 0.22-jwm-pore-size.
8.2.4 Collect a minimum of 1-L of sample.
8.3 Sample preservation and handling
8.3.1 Immediately following sample collection, tighten the sample container lid(s) and place
the sample container(s) upright in an insulated, plastic-lined storage cooler with ice
packs or in a refrigerator to chill prior to packing the cooler for shipment. Do not freeze
the sample.
8.3.2 Use enough solidly frozen ice packs to ensure that the samples will arrive at a
temperature ofl°Cto 10°C. Use a minimum of two ice packs per shipment and add
extra ice packs for multiple samples. Place one or more ice packs on each side of the
container to stabilize samples.
October 2001
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Method 1605 - Aeromonas
8.3.3 Samples must be maintained at a temperature of 1 °C to 10°C during shipment.
Samples must not be frozen.
Note: Sample temperature during shipment is critical. Ice packs must be frozen solid immediately prior
to shipment.
8.4 Verify and record sample arrival temperature when received in the laboratory. Refrigerate
samples at 1 °C to 5 °C upon receipt at the laboratory and analyze as soon as possible after
collection. Samples must be analyzed within 30 hours of sample collection.
9.0 Quality Control
9.1 Each laboratory that uses Method 1605 is required to operate a formal quality assurance (QA)
program. The minimum QA requirements consist of the initial demonstration of capability (IDC)
test (Section 9.4), ongoing analysis of spiked reagent water (ODC test, Section 9.8) and spiked
finished drinking water samples (MS/MSD, Section 9.7), and analysis of negative culture controls
(Section 9.6), dilution/rinse water blanks (Section 9.5), and media sterility checks (Section 9.2.6)
as tests of continued acceptable performance. Spiked sample results are compared to acceptance
criteria for precision, which are based on data generated during the interlaboratory validation of
Method 1605 involving 11 laboratories and 11 finished water matrices. The more stringent QA
requirements in this method, relative to other, currently used methods for bacterial determination,
are an effort to improve overall microbiological QA. The specifications contained in this method
can be met if the analytical system is maintained under control.
Laboratories are not permitted to modify ADA-V media or procedures associated with filtration
(Sections 10.1 through 10.10). However, the laboratory is permitted to modify method procedures
related to the confirmation of colonies (Section 10.11) to improve performance or lower the costs
of measurements provided that 1) presumptively identified yellow colonies submitted to
confirmation are tested for the presence of cytochrome c (oxidase test), and the ability to ferment
trehalose, and the ability produce indole, and 2) all quality control (QC) tests cited in Section
9.2.12 are performed acceptably and QC acceptance criteria are met. For example, laboratories
may prefer to streak colonies that are submitted to confirmation on tryptic soy agar (TSA),
instead of nutrient agar. The laboratory may not omit any quality control analyses.
9.2 General QC requirements—Specific quality control (QC) requirements for Method 1605 are
provided below. QA and QC criteria for facilities, personnel, and laboratory equipment,
instrumentation, and supplies used in microbiological analyses must be followed according to
Standard Methods for the Examination of Water and Wastewater (latest edition approved by EPA
in 40 CFR Part 141, Reference 15.2) and the U.S. EPAManualfor the Certification of
Laboratories Analyzing Drinking Water, Fourth Edition (March 1997) (Reference 15.5).
9.2.1 Initial demonstration of capability (IDC). The laboratory shall demonstrate the
ability to generate acceptable performance with this method by performing an IDC test
before analyzing any field samples. The procedure for performing the IDC is described
in Section 9.4. IDC tests must be accompanied by a dilution/rinse water blank(s)
(Section 9.2.2), negative culture controls (Section 9.2.3), and media sterility checks
(Section 9.2.6).
October 2001
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Method 1605 - Aeromonas
9.2.2 Dilution/rinse water blanks. The laboratory shall analyze dilution/rinse water blanks
to demonstrate freedom from contamination. The procedures for analysis of
dilution/rinse water blanks are described in Section 9.5. At a minimum, dilution/rinse
water blanks must be processed at the beginning and end of each filtration series to
check for possible cross-contamination. A filtration series ends when 30 minutes or
more elapse between sample filtrations. An additional dilution/rinse water blank is also
required for every 20 samples, if more than 20 samples are processed during a filtration
series.
9.2.3 Negative culture controls. The laboratory shall analyze negative culture controls
(Section 9.6) to ensure that ADA-V and the confirmation procedures are performing
properly. Negative culture controls should be run whenever a new batch of media or
reagents is used. On an ongoing basis, the laboratory must perform, at a minimum, one
negative culture control per week during weeks the laboratory analyzes field samples.
9.2.4 Matrix spike/matix spike duplicate (MS/MSD). The laboratory shall analyze one set
of MS/MSD samples when samples are first received from a finished drinking water
source for which the laboratory has never before analyzed samples (Section 9.7).
Subsequently, 5% of field samples from a given source must include an MS/MSD test.
Additional MS/MSD tests are also recommended when drinking water treatment is
adjusted or when other events take place, for example, when scrubbing or replacing
lines. When possible, MS/MSD analyses should be conducted on the same day as ODC
samples, using the same spiking procedure and volume.
9.2.4.1 Precision. MS/MSD sample results should meet the precision criteria set
forth in Section 12, Table 1.
9.2.4.2 Recovery. QC acceptance criteria for Aeromonas recovery are not included
in this method because the number of Aeromonas in the spike is unknown.
However, each laboratory should control chart the mean number of
Aeromonas per MS/MSD set (adjusted for background) and maintain a
record of spike preparation procedures and spike volume. The laboratory
should compare number of Aeromonas in MS/MSD samples to results of
ODC samples (Section 9.2.5 and 9.8) spiked on the same day. This
comparison should help the laboratory recognize when a matrix is
interfering with method recovery. If the laboratory observes consistent ODC
results from week to week, control charting the MS/MSD results by source
may also help to recognize fluctuations in recovery from a particular source.
9.2.5 Ongoing demonstration of capability (ODC). The laboratory shall demonstrate that
the analytical system is in control on an ongoing basis through analysis of ODC
samples (positive control/positive control duplicate, Section 9.8).
9.2.5.1 Frequency. The laboratory shall analyze one set of ODC samples after every
20 field and MS samples or one set per week that samples are analyzed,
whichever occurs more frequently. No more than one set of ODC samples is
required per day, provided that the same equipment (i.e., incubators) are
being used for all the samples.
9.2.5.2 Precision. ODC sample results must meet the precision criteria set forth in
Section 12, Table 1.
9.2.5.3 Recovery. QC acceptance criteria for Aeromonas recovery are not included
in this method because the initial spike dose for ODC samples is unknown.
October 2001
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Method 1605 - Aeromonas
As a result, each laboratory should control chart the mean number of
Aeromonas per ODC sample set and maintain a record of spike preparation
procedures and ODC spike volume. Maintaining this information will
enable the laboratory to recognize when problems arise. Example: A
laboratory that prepares spiking suspensions according to Section 9.3,
spikes QC samples with 5 mL of dilution D2, and typically recovers
approximately 50 Aeromonas per sample, and maintains a control chart of
these counts. If the laboratory continues to prepare spiking suspensions the
same way, but the number of Aeromonas counted declines noticeably (e.g.
20 Aeromonas per sample), then there may be a problem with the media,
reagents, or the spiking suspension.
9.2.6 Media sterility checks. The laboratory shall test media sterility by incubating one unit
(tube or plate) from each batch of medium (ADA-V, nutrient agar slant, nutrient agar,
streak plate, trehalose, and tryptone) at 35°C ± 0.5°C for 24 ± 2 hours and observing
for growth.
9.2.7 Analyst colony counting variability. If the laboratory has two or more analysts, each
are required to count target colonies on the same membrane from one ODC sample per
month (Section 9.9), at a minimum.
9.2.8 Record maintenance. The laboratory shall maintain records to define the quality of
data that are generated. The laboratory shall maintain a record of the date and results of
all QC sample analyses described in Section 9.2. A record of media sterility check,
dilution/rinse water blank, analyst counting variability, IDC, ODC, and MS/MSD
sample results must be maintained. Laboratories shall maintain reagent and material lot
numbers along with samples analyzed using each of the lots. Laboratories shall also
maintain media preparation records.
9.2.9 Performance studies. The laboratory should periodically analyze external QC
samples, such as performance evaluation (PE) samples, when available. The laboratory
should also participate in available interlaboratory performance studies conducted by
local, state, and federal agencies or commercial organizations. The laboratory should
review results, correct unsatisfactory performance, and record corrective actions.
9.2.10 Autoclave sterilization verification. At a minimum, the laboratory shall verify
autoclave sterilization according to the procedure in Section 9.10 on a monthly basis.
9.2.11 Culture maintenance. The laboratory should use 24 ± 2 hour-old nutrient agar slant
cultures for preparation of IDC, ODC, and MS/MSD spiking suspension dilutions. The
laboratory should use 22 to 72 hour-old nutrient agar slant cultures to inoculate
ADA-V streak plates for analysis of negative culture controls. With regard to the
preparation of subcultures, it is recommended that a maximum of three passages be
prepared to help avoid contamination. After three passages, start a new subculture from
the frozen stock.
9.2.12 Method modification.
9.2.12.1 Membrane Filtration. Because recovery criteria are not available for this
method, laboratories are not permitted to modify the membrane filtration
procedures (Section 10.1 through Section 10.10.) or ADA-V media.
9.2.12.2 Confirmation procedures. The confirmation procedures in Section 10.11
may be modified, provided that the laboratory demonstrates the ability to
generate acceptable performance by performing an IDC test (Section 9.2.1)
October 2001 10
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Method 1605 - Aeromonas
and the appropriate negative culture control test(s) (Section 9.2.3) before
analyzing any field samples using the modified confirmation. 100% of the
colonies submitted to confirmation from IDC and negative culture control
samples must give the appropriate confirmation response. These tests must
be accompanied by a dilution/rinse water blank(s) (Section 9.2.2) and media
sterility checks (Section 9.2.6).
9.3 Preparation of Aeromonas spiking suspension for use in spiking IDC, ODC, and MS/MSD
samples—This dilution scheme is adapted from Standard Methods for the Examination of Water
and Wastewater, 19th Edition, Section 9020 B (Reference 15.9). This entire process should be
performed quickly to avoid loss of viable organisms. See Section 16, Flowchart 1, for an example
of this dilution scheme. Please note: Provided that all QC acceptance criteria are met and the
recommended target range of 20 - 60 CPU per plate are typically observed, laboratories may
prepare QC spiking suspensions using commercial products or other procedures such as growing
bacteria In a broth, measuring optical density, and spiking each test sample with an equivalent
volume.
9.3.1 Inoculate Aeromonas hydrophila (ATCC #7966) onto the entire surface of several
nutrient agar slants with a slope approximately 6.3 cm long in a 125 x 16 mm screw-
cap tube. Incubate for 24 ± 2 hours at 35 °C ± 0.5 °C.
9.3.2 From the slant that has the best growth, prepare serial dilutions using four dilution
bottles with 99 mL of sterile buffered dilution water (A, B, C and D below in Sections
9.3.3 and 9.3.4) and one dilution bottle containing 90-mL of sterile buffered dilution
water (D2 below in Section 9.3.5).
9.3.3 Pipette 1 mL of buffered dilution water from bottle "A" to one of the slants. Emulsify
the growth on the slant by gently rubbing the bacterial film with the pipette, being
careful not to tear the agar. Pipette the suspension back into dilution bottle "A." Repeat
this procedure a second time to remove any remaining growth on the agar slant,
without disturbing the agar.
9.3.4 Make serial dilutions as follows:
9.3.4.1 Shake bottle "A" vigorously and pipette 1 mL to bottle "B"
9.3.4.2 Shake bottle "B" vigorously and pipette 1 mL to bottle "C"
9.3.4.3 Shake bottle "C" vigorously and pipette 1 mL to bottle "D"
9.3.4.4 Shake bottle "D" vigorously and pipette 10 mL to bottle "D2"; this should
result in a final dilution of approximately 10 CPU / mL.
9.3.5 Filter 1- to 5-mL portions in triplicate from bottles "D" and "D2" according to the
procedure in Section 10 to determine the number of CPU in the dilutions. The
recommended target dilution and spike volume is one that produces 20 to 60 colonies
per ADA-V plate. (It may be difficult to count plates with more than 60 colonies due to
crowding.) Dilutions should be stored at 1 °C to 5 °C and may be used throughout the
day they are prepared. However, it should be noted that the QC acceptance criteria
were established using dilutions that were prepared immediately prior to spiking
samples.
9.3.6 Analysts may practice the dilution scheme by placing filters on nutrient agar plates
instead of ADA-V plates. After a growth pattern is determined and the analyst can
accurately determine the target concentrations, dilutions from Section 9.3.5 may be
used for spiking IDC, ODC, and MS/MSD samples. However, multiple dilutions
11 October 2001
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Method 1605 - Aeromonas
should be analyzed in replicate when new cultures are received from an outside source
to ensure that the analyst can accurately spike target concentrations.
Note: If it is more convenient for your laboratory, an acceptable alternative to the dilution scheme
presented in Section 9.3, is to pipette 11 mL of dilution D into a dilution bottle D2, which
contains 99 mL of dilution water. There should be approximately 1010 Aeromonas hydrophila
CFUper slant. Therefore, dilution bottles "A" through "D2" should contain approximately 1010,
10s, 106, 104, and 103 CFU per dilution bottle, respectively. Depending on the growing
conditions, these numbers may vary. As a result, until experience has been gained, more dilutions
may need to be filtered to determine the appropriate dilution.
9.4 Initial demonstration of capability (IDC)—The IDC test is performed to demonstrate
acceptable performance with the method prior to analysis of field samples. IDC tests must be
accompanied by a dilution/rinse water blank(s) (Section 9.2.2), negative culture controls (Section
9.2.3), and media sterility checks (Section 9.2.6).
9.4.1 Prepare an Aeromonas QC spiking suspension according to the procedure in Section
9.3.1 through 9.3.4.
9.4.2 For each of the four IDC test samples, spike enough volume of the appropriate dilution
into 500 mL of sterile reagent water to obtain the recommended target range of 20-60
CFU per filter. (It may be difficult to count plates with more than 60 colonies due to
crowding.) Filter immediately after spiking.
9.4.3 Process IDC test samples according to the procedure in Section 10.1 through 10.10 and
record the number of presumptive positives for each sample. Submit 2 colonies per
IDC test sample to the confirmation procedures in Section 10.11.
9.4.4 Using all four IDC sample results, compute the relative standard deviation (RSD) of
Aeromonas CFU per 100 mL. (See glossary for definition of RSD.) Compare the RSD
with the corresponding limits for IDC (Section 12). If the RSD meets the acceptance
criteria, the system performance is acceptable and analysis of samples may begin. If the
RSD falls outside the range, system performance is unacceptable. In this event, identify
and correct the problem and repeat the test.
9.5 Dilution/rinse water blanks—On an ongoing basis, dilution/rinse water blanks must be
processed at the beginning and end of each filtration series to check for possible cross-
contamination. A filtration series ends when 30 minutes or more elapse between sample
filtrations. An additional dilution/rinse water blank is also required for every 20 samples, if more
than 20 samples are processed during a filtration series. For example, if a laboratory plans to run
30 samples during a filtration series, a dilution/rinse water blank should be processed at the
beginning, middle, and end of the filtration series.
9.5.1 Process 100-mL dilution/rinse water blanks according to the procedures in Section 10,
as appropriate.
9.5.2 No growth should appear in dilution/rinse water blanks. If growth appears, prepare new
dilution/rinse water and reanalyze a 100-mL dilution/rinse water blank. If colonies are
present after analyzing the new dilution/rinse water, assess laboratory technique and
reagents. If growth in dilution/rinse water blank(s) is presumptively positive, all
associated sample results should be discarded and sources re-sampled immediately.
October 2001 12
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Method 1605 - Aeromonas
9.6 Negative culture controls— Negative controls should be run whenever a new batch of medium
or reagents is used. On an ongoing basis, the laboratory must perform, at a minimum, one
negative culture control per week during weeks the laboratory analyzes field samples. Negative
culture controls serve two purposes: to ensure the laboratories are familiar with the color and
morphology of non-Aeromoncts bacteria on ADA-V and to ensure that confirmation test results
are appropriate. E. coll is (ATCC #25922) the negative culture control for oxidase, Pseudomonas
aeruginosa (ATCC #27853) is the negative culture control for trehalose fermentation, and
Bacillus cereus (ATCC #11778) is the negative culture control for indole.
9.6.1 Using pure cultures obtained from a qualified outside source (Sections 7.7 and 7.8),
inoculate negative culture controls onto nutrient agar slants and incubate at
35 °C ± 0.5 °C for 24 ± 2 hours. Alternatively, nutrient agar slants may be inoculated up
to 72 hours in advance. If nutrient agar slants will be incubated for more than 24 ± 2
hours, consider incubation at room temperature to ensure that the slants do not dry out
prior to use.
9.6.2 For each negative culture control, place a membrane filter on an ADA-V plate, streak
onto the filter, taking care not to break the filter, and incubate at 35 °C ± 0.5 °C for
24 ± 2 hours. Streaking on a filter will give the laboratory a more realistic example of
the appearance of these organisms in field samples. Although not recommended,
laboratories may streak directly onto the ADA-V (without the filter).
9.6.3 For each ADA-V negative culture control plate, pick a single colony, streak the colony
onto a plate of nutrient agar medium (Section 7.9), and incubate at35°C±0.5°C
overnight to obtain isolated colonies. Please note: Bacillus cereus typically grows only
at the point of inoculation on ADA-V or not at all. If Bacillus cereus did not grow on
the ADA-V plate, inoculate the streak plate from the nutrient agar slant that was
originally used to inoculate the ADA-V plate.
9.6.4 Negative culture control confirmation procedures
9.6.4.1 Oxidase negative culture control—From the streak plate, submit a single
E. coli colony to the oxidase confirmation procedure described in Section
10.11.
9.6.4.2 Trehalose negative culture control—From the streak plate, submit a
single Pseudomonas aeruginosa colony to the trehalose confirmation
procedure described in Section 10.11.
9.6.4.3 Indole negative culture control—From the streak plate, submit a single
Bacillus cereus colony to the indole confirmation procedure described in
Section 10.11.
9.6.5 If any of the negative culture controls result in a positive confirmation, prepare, check
and/or replace the associated media, reagents, and/or respective control organism and
reanalyze the appropriate negative culture control(s). All presumptively positive
colonies that have been archived from field samples (10 per sample) should be
confirmed using media/reagents that exhibit the appropriate negative culture control
response.
9.7 Matrix spike/matrix spike duplicate (MS/MSD)—The laboratory shall analyze MS/MSD
samples when samples are first received from a finished drinking water source for which the
laboratory has never before analyzed samples. Subsequently, 5% of field samples from a given
source must include an MS/MSD test. Additional MS/MSD tests are also recommended when
drinking water treatment is adjusted or when other events take place, for example, when
scrubbing or replacing lines.
13 October 2001
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Method 1605 - Aeromonas
9.7.1 Prepare an Aeromonas QC spiking suspension according to the procedure in Sections
9.3.1 through 9.3.4.
9.7.2 For each of the 500-mL MS and MSB test samples, spike enough volume of the
appropriate dilution to obtain the recommended target range of 20-60 CPU per filter. (It
may be difficult to count plates with more than 60 colonies due to crowding.) Filter
immediately after spiking.
9.7.3 Process MS/MSD test samples and an unspiked finished drinking water sample
according to the procedure in Section 10.1 through 10.10 and record the number of
presumptive positives for each sample. (If the filter clogs during filtration, follow the
instructions in Section 10, making sure to filter the same volume for both the MS and
MSB. The same QC acceptance criteria apply.) Submit 10 colonies per IDC test sample
to the confirmation procedures in Section 10.11.
Note: If results exceed the optimum range because of "background" target colonies (as indicated by
the results of the unspiked matrix sample), the MS/MSD should be repeated and a smaller volume
of sample, for example 200-mL, should be spiked.
9.7.4 For the MS and MSB test samples, calculate the number of confirmed Aeromonas CPU
per 100 mL according to Section 11 and adjust based on any background Aeromonas
observed in the unspiked sample.
9.7.5 Calculate the relative percent difference (RPD) using the following equation:
|X/MS - X/WSD|
RPD = 100-
Xm
where
RPD is the relative percent difference
XMS is the number of confirmed Aeromonas per 100 mL in the MS sample
(minus the count of any background Aeromonas colonies observed in the
unspiked finished water sample)
XMSD is the number of confirmed Aeromonas per 100 mL in the MSB
sample (minus the count of any background Aeromonas colonies observed
in the unspiked finished water sample)
Xmean is the mean number of confirmed Aeromonas per 100 mL in the MS
and MSB
9.7.6 Compare the RPB with the corresponding limits in Table 1 in Section 12. If the RPB
meets the acceptance criteria, the system performance is acceptable and analysis of
finished water samples from this source may continue. If the MS/MSB results are
unacceptable and the OBC sample results associated with this batch of samples are
acceptable, a matrix interference may be causing the poor results. If the MS/MSB
results are unacceptable, all associated field data should be flagged.
9.8 Ongoing demonstration of capability (ODC)—The laboratory shall demonstrate that the
analytical system is in control on an ongoing basis through analysis of OBC samples (positive
control/positive control duplicate). The laboratory shall analyze one set of OBC samples after
October 2001 14
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Method 1605 - Aeromonas
every 20 field and MS samples or one set per week that samples are analyzed, whichever occurs
more frequently.
9.8.1 Prepare an Aeromonas QC spiking suspension according to the procedure in Section
9.3.1 through 9.3.4.
9.8.2 For each of the 500-mL positive control (PC) and positive control duplicate (PC/PCD)
test samples, spike enough volume of the appropriate dilution into 500 mL of sterile
reagent water to obtain the recommended target range of 20-60 CPU per filter. (It may
be difficult to count plates with more than 60 colonies due to crowding.) Filter
immediately after spiking.
9.8.3 Process PC/PCD test samples according to the procedure in Section 10.1 through 10.10
and record the number of presumptive positives for each sample. Submit 2 colonies per
PC/PCD test sample to the confirmation procedures in Section 10.11.
9.8.4 Calculate the relative percent difference (RPD) using the following equation:
\Xpc- XPCD\
RPD = 100L
•Am
where
RPD is the relative percent difference
XPC is the number of confirmed Aeromonas per 100 mL in the PC sample
XPCD is the number of confirmed Aeromonas per 100 mL in the PCD
sample
Xmean is the mean number of confirmed Aeromonas per 100 mL in the PC
and PCD samples
9.8.5 Compare the RPD with the corresponding limits in Table 1 in Section 12. If the RPD
meets the acceptance criteria, the system performance is acceptable and analysis of
samples may continue. If RPD falls outside the range, system performance is
unacceptable. Identify and correct the problem and perform another ODC test before
continuing with the analysis of field samples.
9.8.6 As part of the QA program for the laboratory, method precision for ODC samples
should be charted and records retained.
9.9 Analyst colony counting variability—If the laboratory has two or more analysts, each are
required to count target colonies on the same membrane from one positive field sample per
month. Compare each analyst's count of the target colonies. Counts should fall within 10%
between analysts. If counts fail to fall within 10% of each other, analysts should perform
additional sets of counts, until the number of target colonies counted fall within 10% between
analysts for at least three consecutive samples. If there are no positive samples, an MS, MSD, or
ODC sample can be used for this determination (MS or MSD are preferable to ODC samples,
since they may have other background growth).
9.10 Autoclave sterilization verification—Verify autoclave sterilization monthly by placing Bacillus
stearothermophilus spore suspensions or strips inside glassware. Sterilize at 121 °C for 15
minutes. Place in trypticase soy broth tubes and incubate at 55 °C for 48 hours. Check for growth
to verify that sterilization was adequate. If sterilization was inadequate, determine appropriate
time for autoclave sterilization. Filter sterilization may be used provided that these same QC steps
are instituted for the filtrate.
15 October 2001
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Method 1605 - Aeromonas
10.0 Procedure
10.1 The membrane filter (MF) procedure with ampicillin-dextrin agar with vancomycin (ADA-V) is
used to enumerate Aeromonas in finished waters.
10.2 Label each petri dish with sample identification, preparation date, and analysis start date/time.
10.3 Use a sterile MF unit assembly (Section 6.18.3) at the beginning of each filtration series. The
laboratory must sanitize each MF unit between filtrations by using a UV sanitzer, flowing steam,
or boiling water for 2 min. A filtration series ends when 30 minutes or more elapse between
sample filtrations.
10.4 Sterilize forceps with alcohol. Flame off excess alcohol. Using sterile forceps, place the MF (grid
side up) over the sterilized runnel. Carefully place the top half of the filtration unit over the
funnel and lock it in place.
10.5 Shake the sample bottle vigorously approximately 25 times to distribute the bacteria uniformly.
Using aseptic technique, transfer one, 500-mL aliquot of sample to a single funnel. Use a
graduated cylinder with a "to deliver" tolerance of approximately 2.5%.
Note: Laboratories must filter the entire 500-mL sample volume unless the filter clogs. If the filter
clogs, a minimum of 100 mL of sample must be filtered, which may require multiple filtrations . If
less than 500 mL are filtered and analyzed due to filter clogging, measure the residual, unfiltered
volume to determine the volume filtered, and adjust the reporting limit accordingly.
10.6 Filter each sample under partial vacuum through a sterile membrane filter. Rinse the funnel after
each sample filtration by filtering three, 30-mL portions of sterile buffered dilution water, being
sure to thoroughly rinse the sides of the funnel.
10.7 Upon completion of the final rinse, disengage the vacuum and remove the funnel.
10.8 Using sterile forceps, immediately remove the MF and place it grid-side-up on the ADA-V
medium with a rolling motion to avoid trapping air under the filter. Reseat the membrane filter if
bubbles occur. Place the inverted petri dishes in the 35 °C ± 0.5 °C incubator within 30 minutes of
preparation. Sterilize forceps and sanitize the MF unit between the analysis of each sample.
10.9 After 24 ± 2 hours of incubation at 35 °C ± 0.5 °C, count and record yellow colonies under
magnification using a dissecting microscope.
10.10 Isolation of a yellow colony on ampicillin-dextrin agar with vancomycin (ADA-V) should be
considered presumptively positive for Aeromonas.
10.11 Confirmation—All presumptive colonies, up to ten per sample, must be submitted to
confirmation. In this method, any presumptive colony that is positive for oxidase (Section
10.11.2), ferments trehalose (Section 10.11.3), and produces indole (Section 10.11.4) is
considered to be Aeromonas. If the result for any confirmation procedure is negative, no further
confirmation steps are necessary. Slight variations in color and morphology may be present
between different Aeromonas species grown on ADA-V medium. The colonies selected for
confirmation should be representative of all yellow (presumptively positive) colony morphology
types on ADA-V plate. For example, if 30 bright yellow colonies and 20 dull yellow colonies are
observed, then 6 bright yellow and 4 dull yellow colonies should be submitted to confirmation.
October 2001 16
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Method 1605 - Aeromonas
Note: It is important to record the number of colonies of each presumptively positive morphological
type so that the final density of Aeromonas can be reported based on percent confirmation of
each morphological type. Also, the laboratory may submit more than ten presumptively positive
colonies to the confirmation step.
10.11.1 Nutrient agar streak plate. To confirm as Aeromonas, pick a colony and streak the
colony onto a plate of nutrient agar medium (Section 7.9) and incubate at
35 °C ± 0.5 °C overnight to obtain isolated colonies.
10.11.2 Oxidase confirmation. Apply a very small amount of a discreet colony from the
nutrient agar to the oxidase dry slide using a wooden or plastic applicator. Do not use
iron or other reactive wire because it may cause false positive reactions. Also, do not
transfer any medium with the culture material, as this could lead to inconsistent results.
A blue/purple color reaction within 10 seconds is considered a positive oxidase test.
For commercially-prepared reagent, adhere to manufacturer's expiration date. Freshly-
made solutions should be used within one week. Please note: This method was
validated using nutrient agar, if the oxidase reagent is to be dropped directly on
colonies, use tryptic soy agar plates because nutrient agar plates give inconsistent
results. The use of tryptic soy agar plates for streaking (Section 10.11.1) has not been
validated and is considered a method modification and, as a result, the laboratory must
demonstrate acceptable performance for the QC analyses described in Section 9.2.12.
Note: Timing of the color reaction is critical, as some Gram-positive bacteria may give false positives
after 10 seconds. Also, it is important to put just a small amount of the colony on the oxidase dry
slide or saturated pad, as too much bacteria can also cause a false positive oxidase test.
10.11.3 Trehalose confirmation. If the oxidase test is positive, then test for trehalose
fermentation. Trehalose fermentation is determined by inoculating a tube containing
3-10 mL (depending on the size of the tube used - fill about half full) of 0.5% trehalose
in purple broth base (Section 7.11) with a colony from the nutrient agar and incubating
at 35°C ± 0.5°C for 24 ± 2 hours. A change in color of the medium from purple to
yellow is considered a positive for trehalose fermentation.
10.11.4 Indole confirmation. If the oxidase and trehalose tests are positive, then test for indole
production. (If the laboratory prefers, the indole confirmation procedure may be started
on the same day as the trehalose confirmation.) Indole production is determined by
inoculating a tube containing 3-10 mL (depending on the size of the tube used - fill
about half full) of tryptone broth (Section 7.12) with a colony from the nutrient agar
and incubating at35°C±0.5°C for 24 ± 2 hours. After incubation, add 0.2 to 0.3 mL
(4 to 6 drops) of Kovac's test reagent (Section 7.13) to each tube, let stand for
approximately 10 minutes and observe results. A pink to red color in the surface layer
constitutes a positive indole test. The original color of the Kovac's reagent indicates a
negative indole test. An orange color probably indicates the presence of skatole, a
breakdown product of indole, and is considered a positive result.
10.11.5 If a colony is oxidase, trehalose, and indole positive, report as a confirmed Aeromonas
and archive the colony for further identification.
17 October 2001
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Method 1605 - Aeromonas
Note: If samples are to be archived for further analysis to determine species or hybridization group,
from the nutrient agar plate (Section 10.11.1), inoculate a nutrient agar slant for short term use
or shipment to another laboratory.
11.0 Data Analysis and Calculations
11.1 See Standard Methods for the Examination of Water and Wastewater (Reference 15.2) for
general counting rules. The density of Aeromonas determined by the membrane filter (MF)
procedure is calculated by direct identification and enumeration of yellow colonies by a
dissecting microscope (Section 6.19) followed by oxidase, trehalose, and indole confirmation.
Bacterial density is recorded as presumptive Aeromonas colony forming units (CPU) per 100 mL
of sample and confirmed Aeromonas CPU per 100 mL.
11.2 Counting colonies on ADA-V
11.2.1 Record the number of presumptive Aeromonas CFU/lOOmL. If there is more than one
morphological type that is considered to be presumptively positive, record the number
of presumptive positives for each morphological type, as well as the total number of
presumptive positives.
11.2.2 If there are more than 200 colonies, including background colonies, report results as
too numerous to count (TNTC) and resample. If the filter is TNTC with more
background colonies than presumptive aeromonads, split the 500 mL resample between
3 or 4 filters in order to better differentiate the colony morphology types. If the filter is
TNTC with mostly aeromonads, a minimum of three dilutions (e.g. 100 mL, 10 mL and
1 mL) should be analyzed.
11.2.3 If the colonies are not discrete and appear to be growing together, report results as
confluent growth (CG) and resample.
11.3 Confirmation and calculation of Aeromonas density
11.3.1 In this method, any presumptive colony that is positive for oxidase (Section 10.11.2),
ferments trehalose (Section 10.11.3), and produces indole (Section 10.11.4) is
considered to be Aeromonas. For the final density of confirmed Aeromonas, adjust the
initial, presumptive count based on the positive confirmation percentage for each
presumptively positive morphological type and report as confirmed CPU per 100 mL.
11.3.2 Calculate the number of positive confirmations for each presumptively positive
morphological type from all Jitters of a given sample using the following equation:
( Number positively confirmed ^ 100
— ; ;———— — x Number of presumptive positives x ——7- = Confirmed Aeromonas / 10OmL
^Number submitted to confirmation ) ml filtered
11.3.3 Record the number of confirmed Aeromonas per 100 mL for each colony morphology.
11.3.4 Sum the number of confirmed Aeromonas per 100 mL for all presumptively positive
colony types (Section 11.3.2) and report as the density of confirmed Aeromonas per
100 mL.
11.3.5 Example 1: In this example, 500 mL of sample was filtered and two different
morphological types of presumptively positive colonies were observed.
October 2001 18
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Method 1605 - Aeromonas
Example 1
Morphological Description
Type A: Bright yellow, round, opaque
Type B: Dull yellow, oval, translucent
Number of
presumptively positive
colonies per volume
filtered
30
20
Number
submitted to
confirmation
steps
6
4
Number
positively
confirmed
6
3
Total number of confirmed Aeromonas per sample:
Number of
confirmed
Aeromonas
per 100 ml_
6
3
9 per 100 mL
6 "| 100
Trx 30 x —— = 6 Confirmed Type A Aeromonas / 100ml_
6 I 500
3 "| 100
— x20 x —— = 3 Confirmed Type B Aeromonas / 100ml_
T1 / OUU
Example 1 results in 9 confirmed Aeromonas 1100 mL.
11.3.6 Example 2: In this example, 200 mL of sample was filtered and two different
morphological types of presumptively positive colonies were observed.
Example 2
Morphological Description
Type A: Dull yellow, round, opaque
Type B: Dull yellow, round, translucent
Number of
presumptively
positive colonies per
volume filtered
40
40
Number
submitted to
confirmation
steps
5
5
Number
positively
confirmed
5
3
Total number of confirmed Aeromonas per sample:
Number of
confirmed
Aeromonas
per 100 mL
20
12
32 per 100 mL
5 "\ 100
— x40 x——- = 20 Confirmed Type A Aeromonas / 100ml_
o /
3 "l 100
— x40 x—— = 12 Confirmed Type B Aeromonas / 100ml_
O /
Example 2 results in 32 confirmed Aeromonas 1100 mL.
11.3.7 If there were no presumptively positive colonies or if none of the presumptive colonies
are confirmed, then report the results as less than the detection limit (DL) in CPU per
100 mL based on sample volume filtered. If less than 500 mL are filtered, then adjust
the reporting limit per 100 mL accordingly. The DL may be calculated as follows:
DL per 100 mL = 100 / volume filtered CPU per 100mL
19
October 2001
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Method 1605 - Aeromonas
11.3.7.1 Example 3: If 500 mL of sample was filtered and there were no confirmed
colonies, then report as <0.2 CFU/100 mL.
11.3.7.2 Example 4: If 100 mL of sample was filtered and there were no confirmed
colonies, then report as <1.0 CFU/100 mL.
12.0 Method Performance
12.1 Specificity of media
12.1.1 Please refer to Section 16, Table 2, for results of Aeromonas growth after 24 hours on
ADAat30°C and 35 °C and ADA-Vat 35 °C .
12.1.2 ADA-V was able to support the growth of the Aeromonas species (hydrophila, caviae,
and veronii/sobria) most often associated with human disease.
12.1.3 Efforts continue to identify colonies which give a presumptive positive on the ADA-V
media but do not confirm.
12.2 The QC acceptance criteria listed in Table 1, below are based on data generated through the
interlaboratory validation of Method 1605 involving 11 laboratories and 11 finished drinking
water matrices. Detailed method QC procedures applicable to these criteria are discussed in
Section 9.
Table 1. QC Acceptance Criteria for Method 1605
QC specification
Initial demonstration of capability (IDC): This test will require the analysis of 4
spiked reagent water samples
Ongoing demonstration of capability (ODC): This test will require the analysis
of 2 spiked reagent water samples
Matrix spike/matrix spike duplicate (MS/MSD) precision: This test will require
the analysis of 2 spiked finished water (matrix) samples
Maximum acceptable
precision
RSD = 22%
RPD = 37%
RPD = 48%
13.0 Pollution Prevention
13.1 The solutions and reagents used in this method pose little threat to the environment when
recycled and managed properly.
13.2 Solutions and reagents should be prepared in volumes consistent with laboratory use to minimize
the volume of expired materials to be disposed.
14.0 Waste Management
14.1 It is the laboratory's responsibility to comply with all federal, state, and local regulations
governing waste management, particularly the biohazard waste identification rules and land
disposal restrictions, and to protect the air, water, and land by minimizing and controlling all
releases from fume hoods and bench operations. Compliance with all sewage discharge permits
and regulations is also required.
October 2001 20
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Method 1605 - Aeromonas
14.2 Samples, reference materials, and equipment known or suspected of having bacterial
contamination from this work must be sterilized prior to disposal.
14.3 For further information on waste management, consult "The Waste Management Manual for
Laboratory Personnel" and "Less is Better: Laboratory Chemical Management for Waste
Reduction," both of which are available from the American Chemical Society's Department of
Government Relations and Science Policy, 1155 16th Street N.W., Washington, B.C. 20036.
15.0 References
15.1 Havelaar, A.H., M. During, and J.F.M. Versteegh. 1987. Ampicillin-dextrin agar medium for the
enumeration of Aeromonas species in water by membrane filtration. Journal of Applied
Microbiology. 62:279-287.
15.2 Standard Methods for the Examination of Water and Wastewater. 1998. 20th Edition. Eds. A.D.
Eaton, L.S. Clesceri, and A. Greenberg. American Public Health Association, American Water
Works Association, and Water Environment Federation. American Public Health Association,
Washington, B.C., publisher.
15.3 Demarta, A., M. Tonolla, A. Caminada, N. Ruggeri, and R. Peduzzi. 1999. Signature region
within the 16S rDNA sequences of Aeromonaspopoffii. FEMS Microbiol. Letts. 172:239-246.
15.4 Annual Book of ASTM Standards, Vol. 11.01. American Society for Testing and Materials.
Philadelphia, PA 19103.
15.5 Manual forthe Certification of Laboratories Analyzing Drinking Water. 1997. 4th Edition. EPA-
815-B-97-001. Office of Ground Water and Drinking Water. U.S. EPA.
15.6 Moyer, N. P. 1996. Isolation and enumeration of aeromonads. In: The Genus Aeromonas. Eds. B.
Austin, M. Altwegg, P. Gosling, and S. Joseph. John Wiley and Sons publisher, Chichester, U.K.
15.7 Reagent Chemicals, American Chemical Society Specifications. American Chemical Society,
Washington, D.C.
15.8 Handfield, M., P. Simard, and R. Letarte. 1996. Differential media for quantitative recovery of
waterborne Aeromonas hydrophila. Applied Environmental Microbiology 62:3544-3547.
15.9 Standard Methods for the Examination of Water and Wastewater. 1995. 19th Edition. Eds. A.D.
Eaton, L.S. Clesceri, and A. Greenberg. American Public Health Association, American Water
Works Association, and Water Environment Federation. American Public Health Association,
Washington, D.C., publisher.
15.10 Janda, J.M. and S.L. Abbott. 1998. Evolving concepts regarding the genus Aeromonas: an
expanding panorama of species, disease presentations, and unanswered questions. Journal of
Clinical Infectious diseases. 27:332-344.
21 October 2001
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Method 1605 - Aeromonas
16.0 Tables and Flowcharts
Table 2. Growth of Aeromonas cultures in 24 hours on ADA at 30°C and 35°C and ADA-V at 35°C
Collection #
ATCC 7966
ATCC 35654
AMC 12723-W
ATCC 51 108
AMC 14228-V
ATCC 336581
AMC 15228-V
ATCC 15468
MML 1685-E
ATCC 33907
AMC Leftwich
ATCC 233091
ATCC 35993
Muldoon SMHC
ATCC 9071
AMC 1123-W
ATCC 43700
AMC 1108-W
ATCC 49657s
NMRI 206
ATCC 51 208
ATCC 49568
AS 14
ATCC 35622
WR 4659
CECT 4342
LMG175414
AMC (ATCC 35941)
AMC (ATCC 43946)
CDC 0434-84
Hybridization
group
Group 1
Group 1
Group 1
Group 2
Group 2
Group 3
Group 3
Group 4
Group 4
Group 5
Group 5
Group 6
Group 7
Group 7
Group 8
Group 8
Group 12
Group 12
unknown
unknown
unknown
Group 9
Group 9
Group 10
Group 10
Group 11
unknown
unknown
unknown
Group 3
Aeromonas species
hydrophila
hydrophila
hydrophila
bestiarum
bestiarum
salmonicida/salmonicida
salmonicida
caviae
caviae
media
media
eucrenophila
sobria
sobria
veronii/sobria
veronii/sobria
schubertii
schubertii
trota
trota
allosaccharophila
jandaei
jandaei
veronii/veronii
veronii/veronii
encheleia
popoffii
ornithine positive
Group 501
Motile Group 3
ADA
at 30°C
+
+
+
+
+
-
+
+
+
-
-
+
+
+
+
+
+2
+
-
-
+
+
+
+
+
+
+
-
+
+
ADA
at 35°C
+
+
+
+
+
-
+
+
+
-
-
-
+
+
+
+
+5
-
-
-
+
+
+
+
+
-
+
-
+
+
ADA-V
at 35°C
+
+
+
+
+
NA
+
+
+
NA
NA
NA
+
+
+
+
+5
NA
NA
NA
+
+
+
+
+
NA
+
NA
+
+
(1) Respective Aeromonas cultures grew on ADA medium when streaked, but not when filtered.
October 2001
22
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Method 1605 - Aeromonas
(2) Respective Aeromonas cultures grew when streaked on ADA medium at 30°C, however filtration was not
performed with these cultures.
(3) Respective Aeromonas cultures did not grow on ADA medium when streaked.
(4) Respective Aeromonas cultures grew poorly on ADA medium at both temperatures and on ADA-V at 35°C. The
same pattern of poor growth was also observed on non-selective media.
(5) Respective Aeromonas cultures grew poorly on ADA and ADA-V medium at 35°C. The same pattern of poor
growth was also observed on non-selective media.
Results:
NA Based on ADA results, it was assumed that the culture would not grow on ADA-V at 35°C.
+ positive growth
No growth
ATCC = American Type Culture Collection, Manassas, VA Other cultures were obtained from Amy Carnahan,
University of Maryland. Serial dilutions representing approximately 10-200 CPU were filtered and the membrane
placed on ADA or ADA-V medium as described in Section 10. Additional membranes representing the same
dilution for each of the respective cultures were placed on brain heart infusion agar as a control.
23 October 2001
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17.0 Glossary
17.1 Symbols
°C degrees Celsius
jwm micrometer
± plus or minus
< less than
% percent
17.2 Alphabetical characters and acronyms
ASTM American Society for Testing and Materials
ATCC American Type Culture Collection
CFR Code of Federal Regulations
CG confluent growth
EDTA ethylenediaminetetraacetic acid
g gram
L liter
mg milligram
mL milliliter
mm millimeter
Na2S2O3 sodium thiosulfate
NIST National Institute of Standards and Technology
OSF£A Occupational Safety and Health Administration
psi pounds per square inch
RSD relative standard deviation
QC quality control
TNTC too numerous to count
USEPA United States Environmental Protection Agency
X "times"
17.3 Definitions
Confirmed colonies—Presumptively positive colonies that test positive for oxidase, ferment trehalose,
and produce indole
Dilution/rinse water blank—A 100-mL aliquot of dilution/rinse water that is treated exactly as a sample
and carried through all portions of the procedure until determined to be negative or positive. The
Dilution/rinse water blank is used to determine if the sample has become contaminated by the
introduction of a foreign microorganism through poor technique.
Initial demonstration of capability (IDC)—The IDC test is performed to demonstrate acceptable
performance with the method prior to analysis of field samples.
Must—This action, activity, or procedural step is required.
Negative culture control—A non-Aeromonas bacteria processed to ensure the laboratories are familiar
with the color and morphology of non-Aeromonas bacteria on ADA-V and to ensure that confirmation
test results are appropriate.
25 October 2001
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Method 1605 - Aeromonas
Ongoing demonstration of capability (ODC)—The laboratory shall demonstrate that the analytical system
is in control on an ongoing basis through analysis of ODC samples (positive control/positive control
duplicate).
Positive control—A 500-mL reagent water spiked with 20 - 80 CPU of Aeromonas. The positive control
is analyzed exactly like a sample. Its purpose is to ensure that the results produced by the laboratory
remain within the limits specified in this method for precision and recovery.
Presumptive positive colonies—Colonies that are yellow on ADA-V.
Relative Standard Deviation (RSD)—The standard deviation times 100 divided by the mean.
Selective medium—A culture medium designed to suppress the growth of unwanted microorganisms and
encourage the growth of the target bacteria.
Should—This action, activity, or procedural step is suggested but not required.
October 2001 26
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