January 7, 2010 1 of 1 

Indicator data collected concurrently with virus 

monitoring under the Third Unregulated 

Contaminant Monitoring Regulation 

Indicator: Total Coliforms and E.coli 

Background 

Under the Unregulated Contaminant Monitoring Regulation (UCMR), EPA collects national 

occurrence information on targeted contaminants in drinking water. The Safe Drinking Water 

Act (SDWA) requires EPA identify no more than 30 unregulated drinking water contaminants to 

be monitored by public water systems. This data set supports Environmental Protection 

Agency’s (EPA) regulatory determination process. The data set helps indicate how many people 

are potentially exposed to these contaminants and provides an estimate of the levels of exposure. 

In the third UCMR (UCMR 3), EPA proposes monitoring of 28 chemical and two microbial 

contaminants. The microbial contaminants are enterovirus and norovirus. Concurrent with virus 

monitoring, EPA proposes to collect data on five pathogen indicators for a better understanding 

of pathogen indicator and viral co-occurrence. These indicators are enterococci, E.coli and total 

coliforms, bacteriophages and aerobic endospores. 

Monitoring for total coliforms and E.coli: 

Total coliforms and E.coli are widely used indicators of distribution system integrity and fecal 

contamination. EPA is considering using EPA method 1604 or a similar method from a list of 

several approved methods based on enzyme –substrate utilization for the simultaneous detection 

of total coliforms and E. coli. 
EPA

United States Office of Water 

Environmental Protection Washington DC September 2002 

Agency 20460 

EPA 821-R-02-024 

Method 1604: Total Coliforms and 

Escherichia coli in Water by 

Membrane Filtration Using a 

Simultaneous Detection 

Technique (MI Medium) 
U.S. Environmental Protection Agency 

Office of Water (4303T) 

1200 Pennsylvania Avenue, NW 

Washington, DC 20460 

EPA-821-R-02-024
Disclaimer 

The Engineering and Analysis Division, of the Office of Science and Technology, has reviewed and 

approved this report for publication. The Office of Science and Technology directed, managed, and 

reviewed the work of DynCorp in preparing this report. Neither the United States Government nor any of 

its employees, contractors, or their employees make any warranty, expressed or implied, or assumes any 

legal liability or responsibility for any third party’s use of or the results of such use of any information, 

apparatus, product, or process discussed in this report, or represents that its use by such party would not 

infringe on privately owned rights. 

The content of this method version is identical to the February 2000 version of Membrane Filter Method 

for the Simultaneous Detection of Total Coliforms and Escherichia coli in Drinking Water (EPA-600-R00-013) with one exception, the addition of MI broth. Since MI broth was approved on November 6, 

2001, as a minor modification of the MI agar method, it has also been included in this document. 

Mention of trade names or commercial products does not constitute endorsement or recommendation for 

use. 

Questions concerning this method or its application should be addressed to: 

Robin K. Oshiro

Engineering and Analysis Division (4303T)

U.S. EPA Office of Water, Office of Science and Technology

1200 Pennsylvania Avenue, NW

Washington, DC 20460

oshiro.robin@epa.gov

202-566-1075

202-566-1053 (facsimile)
Table of Contents 

1.0 Scope and Application ......................................................... 1

2.0 Summary of Method ........................................................... 1

3.0 Definitions ................................................................... 1

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 ....................................... 6

9.0 Calibration and Standardization .................................................. 6

10.0 Quality Control (QC) .......................................................... 6

11.0 Procedure ................................................................... 7

12.0 Data Analysis and Calculations .................................................. 8

13.0 Method Performance ........................................................... 8

14.0 Pollution Prevention ........................................................... 9

15.0 Waste Management ............................................................ 9

16.0 References .................................................................. 10

17.0 Tables and Figures ........................................................... 12
Method 1604: Total Coliforms and Escherichia coli in Water by

Membrane Filtration Using a Simultaneous Detection Technique

(MI Medium) 

September 2002 

1.0 Scope and Application 

1.1 This test method describes a sensitive and differential membrane filter (MF) medium, using MI 

agar or MI broth, for the simultaneous detection and enumeration of both total coliforms (TC) 

and Escherichia coli (E. coli) in water samples in 24 hours or less on the basis of their specific 

enzyme activities. Two enzyme substrates, the fluorogen 4-Methylumbelliferyl-$-Dgalactopyranoside (MUGal) and a chromogen Indoxyl-$-D-glucuronide (IBDG), are included in 

the medium to detect the enzymes $-galactosidase and $-glucuronidase, respectively, produced 

by TC and E. coli, respectively. 

1.2 Total coliforms include species that may inhabit the intestines of warm-blooded animals or occur 

naturally in soil, vegetation, and water. They are usually found in fecally-polluted water and are 

often associated with disease outbreaks. Although they are not usually pathogenic themselves, 

their presence in drinking water indicates the possible presence of pathogens. E. coli, one species 

of the coliform group, is always found in feces and is, therefore, a more direct indicator of fecal 

contamination and the possible presence of enteric pathogens. In addition, some strains of E. coli 

are pathogenic (Reference 16.12). 

1.3 This method, which has been validated for use with drinking water in single-lab and multi-lab 

studies (References 16.8 - 16.10), will be used primarily by certified drinking water laboratories 

for microbial analysis of potable water. Other uses include recreational, surface or marine water, 

bottled water, groundwater, well water, treatment plant effluents, water from drinking water 

distribution lines, drinking water source water, and possibly foods, pharmaceuticals, clinical 

specimens (human or veterinary), other environmental samples (e.g., aerosols, soil, runoff, or 

sludge) and/or isolation and separation of transformants though the use of E. coli lac Z or gus 

A/uid reporter genes (Reference 16.11). 

1.4 Since a wide range of sample volumes or dilutions can be analyzed by the MF technique, a wide 

range of E. coli and TC levels in water can be detected and enumerated. 

2.0 Summary of Method 

2.1 An appropriate volume of a water sample (100 mL for drinking water) is filtered through a 47-

mm, 0.45-μm pore size cellulose ester membrane filter that retains the bacteria present in the 

sample. The filter is placed on a 5-mL plate of MI agar or on an absorbent pad saturated with 2-3 

mL of MI broth, and the plate is incubated at 35°C for up to 24 hours. The bacterial colonies that 

grow on the plate are inspected for the presence of blue color from the breakdown of IBDG by 

the E. coli enzyme $-glucuronidase and fluorescence under longwave ultraviolet light (366 nm) 

from the breakdown of MUGal by the TC enzyme $-galactosidase (Reference 16.8). 

3.0 Definitions 

3.1 Total coliforms (TC) - In this method, TC are those bacteria that produce fluorescent colonies 

upon exposure to longwave ultraviolet light (366 nm) after primary culturing on MI agar or broth 

(See Figure 1.). The fluorescent colonies can be completely blue-white (TC other than E. coli) or 

blue-green (E. coli) in color or fluorescent halos may be observed around the edges of the blue1 September 2002 
Method 1604 

green E. coli colonies. In addition, non-fluorescent blue colonies, which rarely occur, are added 

to the total count because the fluorescence is masked by the blue color from the breakdown of 

IBDG (Reference 16.8). 

3.2 Escherichia coli - In this method, the E. coli are those bacteria that produce blue colonies under 

ambient light after primary culturing on MI agar or broth (See Figures 1 and 2.). These colonies 

can be fluorescent or non-fluorescent under longwave ultraviolet light (366 nm) (Reference 16.8). 

4.0 Interferences and Contamination 

4.1 Water samples containing colloidal or suspended particulate material can clog the membrane 

filter, thereby preventing filtration, or cause spreading of bacterial colonies which could interfere 

with identification of target colonies. However, the blue E. coli colonies can often be counted on 

plates with heavy particulates or high concentrations of total bacteria (See Figures 2 and 3.) 

(Reference 16.8). 

4.2 The presence of some lateral diffusion of blue color away from the target E. coli colonies can 

affect enumeration and colony picking on plates with high concentrations of E. coli. This 

problem should not affect filters with low counts, such as those obtained with drinking water or 

properly diluted samples (Reference 16.8). 

4.3 Tiny, flat or peaked pinpoint blue colonies (# 0.5-mm in diameter on filters containing # 200 

colonies) may be due to species other than E. coli. These colonies occur occasionally in low 

numbers and should be excluded from the count of the E. coli colonies, which are usually much 

larger in size (1-3-mm in diameter). The small colonies have never been observed in the absence 

of typical E. coli, but, if such should occur, the sample should not be considered E. coli-positive 

unless at least one colony has been verified by another method [e.g., EC medium with 

4-Methylumbelliferyl-$-D-glucuronide (MUG) or API 20E strips] (Reference 16.8). 

4.4 Bright green, fluorescent, non-blue colonies, observed along with the typical blue/white or bluegreen fluorescent TC colonies, may be species other than coliforms. These colonies, which 

generally occur in low numbers (# 5%) and can usually be distinguished from the TC, should be 

eliminated from the TC count. An increase in the number of bright green colonies may indicate 

an unusual sample population or a breakdown of the cefsulodin in the medium (Reference 16.8). 

5.0 Safety 

5.1 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 

materials, and while operating sterilization equipment. 

5.2 Mouth-pipetting is prohibited. 

5.3 Avoid prolonged exposure to longwave or germicidal ultraviolet light. 

5.4 Autoclave all contaminated plates and materials at the end of the analysis. 

September 2002 2 
Method 1604 

6.0 Equipment and Supplies

6.1 Incubator set at 35°C ± 0.5°C, with approximately 90% humidity if loose-lidded petri dishes are

used.

6.2 Stereoscopic microscope, with magnification of 10-15x, wide-field type. 

6.3 A microscope lamp producing diffuse light from cool, white fluorescent lamps adjusted to give

maximum color.

6.4 Hand tally.

6.5 Pipet container of stainless steel, aluminum, or Pyrex glass, for pipets. 

6.6 Graduated cylinders (100-mL for drinking water), covered with aluminum foil or kraft paper and

sterilized.

6.7 Membrane filtration units (filter base and funnel), glass, plastic or stainless steel. These are

wrapped with aluminum foil or kraft paper and sterilized.

6.8 Germicidal ultraviolet (254 nm) light box for sanitizing the filter funnels is desirable, but

optional. 

6.9 Line vacuum, electric vacuum pump, or aspirator is used as a vacuum source. In an emergency, a

hand pump or a syringe can be used. Such vacuum-producing devices should be equipped with a

check valve to prevent the return flow of air. 

6.10 Vacuum filter flask, usually 1 liter, with appropriate tubing. Filter manifolds to hold a number of

filter bases are desirable, but optional. 

6.11 Safety trap flask, placed between the filter flask and the vacuum source.

6.12 Forceps, straight (preferred) or curved, with smooth tips to permit easy handling of filters without

damage.

6.13 Alcohol, 95% ethanol, in small wide-mouthed vials, for sterilizing forceps. 

6.14 Bunsen or Fisher-type burner or electric incinerator unit.

6.15 Sterile T.D. (To Deliver) bacteriological or Mohr pipets, glass or plastic (1-mL and 10-mL

volumes).

6.16 Membrane Filters (MF), white, grid-marked, cellulose ester, 47-mm diameter, 0.45 μm ± 0.02-

μm pore size, presterile or sterilized for 10 minutes at 121°C (15-lb pressure). 

6.17 Longwave ultraviolet lamp (366 nm), handheld 4-watt (preferred) or 6-watt, or microscope

attachment. 

6.18 Dilution water: Sterile phosphate-buffered dilution water, prepared in large volumes (e.g., 1 liter)

for wetting membranes before addition of the sample and for rinsing the funnel after sample

filtration or in 99-mL dilution blanks [Section 9050C in Standard Methods (Reference 16.2)].

6.19 Indelible ink marker for labeling plates. 

6.20 Thermometer, checked against a National Institute of Science and Technology (NIST)-certified

thermometer, or one traceable to an NIST thermometer.

6.21 Petri dishes, sterile, plastic, 9 x 50 mm, with tight-fitting lids, or 15 x 60 mm, glass or plastic,

with loose-fitting lids; 15 x 100 mm dishes may also be used. 

3 September 2002 
Method 1604 

6.22 Bottles, milk dilution, borosilicate glass, screw-cap with neoprene liners, marked at 99 mL for 

1:100 dilutions (if needed). Dilution bottles marked at 90 mL, or tubes marked at 9 mL may be 

used for 1:10 dilutions. 

6.23 Flasks, borosilicate glass, screw-cap, 250- to 2000-mL volume, for agar preparation. 

6.24 Waterbath maintained at 50°C for tempering agar. 

6.25 Syringe filter, sterile, disposable, 25-mm diameter, 0.22-μm pore size, to filter cefsulodin for MI 

agar. 

6.26 Syringe, sterile, plastic, disposable, 20-cc capacity. Autoclaved glass syringes are also 

acceptable. 

6.27 Test tubes, sterile, screw-cap, 20 x 150-mm, borosilicate glass or plastic, with lids. 

6.28 Sterilization filter units, presterile, disposable, 500- or 1000-mL capacity, 0.2-μm pore size, to 

filter stock buffer solutions. 

6.29 Sterile 47-mm diameter absorbent pads (used with MI broth). 

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. 

7.0 Reagents and Standards 

7.1 Purity of Reagents: Reagent grade chemicals shall be used in all tests. Unless otherwise 

indicated, reagents shall conform to the specifications of the Committee on Analytical Reagents 

of the American Chemical Society (Reference 16.1). The agar used in preparation of culture 

media must be of microbiological grade. 

7.2 Whenever possible, use commercial culture media as a means of quality control. 

7.3 Purity of Water: Reagent-grade distilled water conforming to Specification D1193, Type II water 

or better, ASTM Annual Book of Standards (Reference 16.3). 

7.4 Buffered Dilution Water (Reference 16.2) 

7.4.1 Stock Phosphate Buffer Solution (Reference 16.2): 

Potassium Dihydrogen Phosphate (KH2PO4) 34.0 g 

Reagent-Grade Distilled Water 500 mL 

7.4.2 Preparation of Stock Buffer Solution: Adjust the pH of the solution to 7.2 with 1 N 

NaOH, and bring volume to 1000 mL with reagent-grade distilled water. Sterilize by 

filtration or autoclave for 15 minutes at 121°C (15-lb pressure). 

7.4.3 MgCl2 Solution (Reference 16.2): Dissolve 38 g anhydrous MgCl2 (or 81.1 g 

MgCl2C6H2O) in one liter of reagent-grade distilled water. Sterilize by filtration or 

autoclave for 15 minutes at 121°C (15-lb pressure). 

7.4.4 Storage of Stock Buffer and MgCl2 Solutions: After sterilization of the stock solutions, 

store in the refrigerator until used. Handle aseptically. If evidence of mold or other 

September 2002 4 
Method 1604 

contamination appears in either stock, the solution should be discarded, and a fresh 

solution should be prepared. 

7.4.5 Working Solution (Final pH 7.0 ± 0.2): Add 1.25 mL phosphate buffer stock (Section 

7.4.2) and 5 mL MgCl2 stock (Section 7.4.3) for each liter of reagent-grade distilled water 

prepared. Mix well, and dispense in appropriate amounts for dilutions in screw-cap 

dilution bottles or culture tubes, and/or into larger containers for use as rinse water. 

Autoclave at 121°C (15-lb pressure) for 15 minutes. Longer sterilization times may be 

needed depending on the container and load size and the amount of time needed for the 

liquid to reach 121°C. 

7.5 MI Agar (Reference 16.8) 

7.5.1 Composition: 

Proteose Peptone #3

Yeast Extract

$-D-Lactose

4-Methylumbelliferyl-$-D-Galactopyranoside (MUGal)

(Final concentration 100μg/mL) 

Indoxyl-$-D-Glucuronide (IBDG) 

(Final concentration 320 μg/mL) 

NaCl 

K2HPO4 

KH2PO4 

Sodium Lauryl Sulfate 

Sodium Desoxycholate 

5.0 g 

3.0 g 

1.0 g 

0.1 g 

0.32 g 

7.5 g 

3.3 g 

1.0 g 

0.2 g 

0.1 g 

Agar 15.0 g 

Reagent-Grade Distilled Water 1000 mL 

7.5.2 Cefsulodin Solution (1 mg / 1 mL): Add 0.02 g of cefsulodin to 20 mL reagent-grade 

distilled water, sterilize using a 0.22-μm syringe filter, and store in a sterile tube at 4°C 

until needed. Prepare fresh solution each time. Do not save the unused portion. 

7.5.3 Preparation: Autoclave the medium for 15 minutes at 121°C (15-lb pressure), and add 5 

mL of the freshly-prepared solution of Cefsulodin (5 μg/mL final concentration) per liter 

of tempered agar medium. Pipet the medium into 9 x 50-mm Petri dishes (5 mL/plate). 

Store plates at 4°C for up to 2 weeks. The final pH should be 6.95 ± 0.2. 

7.6 MI Broth: The composition of MI broth is the same as MI agar, but without the agar. The final 

pH of MI broth should be 7.05 ± 0.2. The broth is prepared and sterilized by the same methods 

described for MI agar in Sections 7.5.1, 7.5.2, and 7.5.3, except that absorbent pads are placed in 

9 x 50 mm Petri dishes and saturated with 2-3 mL of MI broth containing 5 :g/mL final 

concentration of Cefsulodin. Alternately, the broth can be filter-sterilized. Excess broth is poured 

off before using the plates. Plates should be stored in the refrigerator and discarded after 96 

hours (Reference 16.15). 

5 September 2002 
Method 1604 

7.7 Tryptic Soy Agar/Trypticase Soy Agar (Difco 0369-17-6, BD 4311043, Oxoid CM 0129B, or 

equivalent) (TSA) 

7.7.1 Composition: 

Tryptone 15.0 g 

Soytone 5.0 g 

NaCl 5.0 g 

Agar 15.0 g 

7.7.2 Preparation: Add the dry ingredients listed above to 1000 mL of reagent-grade distilled 

water, and heat to boiling to dissolve the agar completely. Autoclave at 121°C (15-lb 

pressure) for 15 minutes. Dispense the agar into 9 x 50-mm petri dishes (5 mL/plate). 

Incubate the plates for 24 - 48 hours at 35°C to check for contamination. Discard any 

plates with growth. If > 5% of the plates show contamination, discard all plates, and 

make new medium. Store at 4°C until needed. The final pH should be 7.3 ± 0.2. 

8.0 Sample Collection, Preservation, and Storage 

8.1 Water samples are collected in sterile polypropylene sample containers with leakproof lids. 

8.2 Sampling procedures are described in detail in Sections 9060A and 9060B of the 18th edition of 

Standard Methods for the Examination of Water and Wastewater (Reference 16.2) or in the 

USEPA Microbiology Methods Manual, Section II, A (Reference 16.6). Residual chlorine in 

drinking water (or chlorinated effluent) samples should be neutralized with sodium thiosulfate (1 

mL of a 10% solution per liter of water) at the time of collection. Adherence to sample 

preservation procedures and holding time limits are critical to the production of valid data. 

Samples not collected according to these rules should not be analyzed. 

8.2.1 Storage Temperature and Handling Conditions: Ice or refrigerate water samples at a 

temperature of 1-4°C during transit to the laboratory. Use insulated containers to assure 

proper maintenance of storage temperature. Take care that sample bottles are not totally 

immersed in water from melted ice during transit or storage. 

8.2.2 Holding Time Limitations: Analyze samples as soon as possible after collection. 

Drinking water samples should be analyzed within 30 h of collection (Reference 16.13). 

Do not hold source water samples longer than 6 h between collection and initiation of 

analyses, and the analyses should be complete within 8 h of sample collection. 

9.0 Calibration and Standardization 

9.1 Check temperatures in incubators twice daily to ensure operation within stated limits (Reference 

16.14). 

9.2 Check thermometers at least annually against an NIST-certified thermometer or one traceable to 

NIST. Check mercury columns for breaks. 

10.0 Quality Control (QC) 

10.1 Pretest each batch of MI agar or broth for performance (i.e., correct enzyme reactions) with 

known cultures (E. coli, TC, and a non-coliform). 

10.2 Test new lots of membrane filters against an acceptable reference lot using the method of Brenner 

and Rankin (Reference 16.7). 

10.3 Perform specific filtration control tests each time samples are analyzed, and record the results. 

September 2002 6 
Method 1604 

10.3.1 Filter Control: Place one or more membrane filters on TSA plates, and incubate the 

plates for 24 hours at 35°C. Absence of growth indicates sterility of the filter(s). 

10.3.2 Phosphate-Buffered Dilution Water Controls: Filter a 50-mL volume of sterile dilution 

water before beginning the sample filtrations and a 50-mL volume of dilution water after 

completing the filtrations. Place the filters on TSA plates, and incubate the plates for 24 

hours at 35°C. Absence of growth indicates sterility of the dilution water. 

10.3.3 Agar or Broth Controls: Place one or more TSA plates and one or more MI agar plates or 

MI broth pad plates in the incubator for 24 hours at 35°C. Broth pad plates should be 

incubated grid-side up, not inverted like the agar plates. Absence of growth indicates 

sterility of the plates. 

10.4 See recommendations on quality control for microbiological analyses in the “Manual for the 

Certification of Laboratories Analyzing Drinking Water: Criteria and Procedures; Quality 

Assurance” (Reference 16.15) and the USEPA Microbiology Methods Manual, part IV, C 

(Reference 16.6). 

11.0 Procedure 

11.1 Prepare MI agar or MI broth and TSA as described in Sections 7.5, 7.6, and 7.7. If plates are 

made ahead of time and stored in the refrigerator, remove them and allow them to warm to room 

temperature. The crystals that form on MI agar after refrigeration will disappear as the plates 

warm up (Reference 16.8). 

11.2 Label the bottom of the MI agar or MI broth plates with the sample number/identification and the 

volume of sample to be analyzed. Label QC TSA plates and the MI agar or MI broth sterility 

control plate(s). 

11.3 Using a flamed forceps, place a membrane filter, grid-side up, on the porous plate of the filter 

base. If you have difficulties in removing the separation papers from the filters due to static 

electricity, place a filter with the paper on top of the funnel base and turn on the vacuum. The 

separation paper will curl up, allowing easier removal. 

11.4 Attach the funnel to the base of the filter unit, taking care not to damage or dislodge the filter. 

The membrane filter is now located between the funnel and the base. 

11.5 Put approximately 30 mL of sterile dilution water in the bottom of the funnel. 

11.6 Shake the sample container vigorously 25 times. 

11.7 Measure an appropriate volume (100 mL for drinking water) or dilution of the sample with a 

sterile pipette or graduated cylinder, and pour it into the funnel. Turn on the vacuum, and leave it 

on while rinsing the funnel twice with about 30 mL sterile dilution water. 

11.8 Remove the funnel from the base of the filter unit. A germicidal ultraviolet (254 nm) light box 

can be used to hold and sanitize the funnel between filtrations. At least 2 minutes of exposure 

time is required for funnel decontamination. Protect eyes from UV irradiation with glasses, 

goggles, or an enclosed UV chamber. 

11.9 Holding the membrane filter at its edge with a flamed forceps, gently lift and place the filter gridside up on the MI agar plate or MI broth pad plate. Slide the filter onto the agar or pad, using a 

rolling action to avoid trapping air bubbles between the membrane filter and the underlying agar 

or absorbent pad. Run the tip of the forceps around the outside edge of the filter to be sure the 

filter makes contact with the agar or pad. Reseat the membrane if non-wetted areas occur due to 

air bubbles. 

7 September 2002 
Method 1604 

11.10 Invert the agar petri dish, and incubate the plate at 35°C for 24 hours. Pad plates used with MI 

broth should be incubated grid-side up at 35°C for 24 hours. If loose-lidded plates are used for 

MI agar or broth, the plates should be placed in a humid chamber. 

11.11 Count all blue colonies on each MI plate under normal/ambient light, and record the results (See 

Figures 1 and 2.). This is the E. coli count. Positive results that occur in less than 24 hours are 

valid, but the results cannot be recorded as negative until the 24-hour incubation period is 

complete (Reference 16.14). 

11.12 Expose each MI plate to longwave ultraviolet light (366 nm), and count all fluorescent colonies 

[blue/green fluorescent E. coli, blue/white fluorescent TC other than E. coli, and blue/green with 

fluorescent edges (also E. coli)] (See Figure 1.). Record the data. 

11.13 Add any blue, non-fluorescent colonies (if any) found on the same plate to the TC count 

(Reference 16.8). 

12.0 Data Analysis and Calculations 

12.1 Use the following general rules to calculate the E. coli or TC per 100 mL of sample: 

12.1.1 Select and count filters with # 200 total colonies per plate. 

12.1.2 Select and count filter with # 100 target colonies (ideally, 20-80). 

12.1.3 If the total number of colonies or TC on a filter are too-numerous-to-count or confluent, 

record the results as “TC+

 (TNTC)” and count the number of E. coli. If both target 

organisms are $ 200, record the results as “TC+

 EC+ (TNTC)”. 

12.1.4 Calculate the final values using the formula: 

Number of blue colonies 

E. coli/100 mL = x 100 

Volume of sample filtered (mL) 

Number of fluorescent colonies + Number of 

TC/100 mL = blue, non-fluorescent colonies (if any) x 100 

Volume of sample filtered (mL) 

12.2 See the USEPA Microbiology Manual, Part II, Section C, 3.5, for general counting rules 

(Reference 16.6). 

12.3 Report results as E. coli or TC per 100 mL of drinking water. 

13.0 Method Performance 

13.1 The detection limits of this method are one E. coli and/or one total coliform per sample volume or 

dilution tested (Reference 16.8). 

13.2 The false-positive and false-negative rates for E. coli are both reported to be 4.3% (Reference 

16.8). 

13.3 The single lab recovery of E. coli is reported (Reference 16.8) to be 97.9% of the Heterotrophic 

Plate Count (pour plate) (Reference 16.2) and 115% of the R2A spread plate (Reference 16.2). 

For Klebsiella pneumoniae and Enterobacter aerogenes, two total coliforms, the recoveries are 

87.5% and 85.7% of the HPC (Reference 16.8), respectively, and 89.3% and 85.8% of the R2A 

spread plate, respectively. 

September 2002 8 
Method 1604 

13.4 The specificities for E. coli and total coliforms are reported to be 95.7% and 93.1% (Reference 

16.8), respectively. 

13.5 The single lab coefficients of variation for E. coli and total coliforms are reported to be 25.1% 

and 17.6% (Reference 16.8), respectively, for a variety of water types. 

13.6 In a collaborative study (References 16.4, 16.5, and 16.9), 19 laboratories concurrently analyzed 

six wastewater-spiked Cincinnati tap water samples, containing 3 different concentrations of E. 

coli (# 10, 11-30, and > 30 per 100 mL). 

13.6.1 The single laboratory precision (coefficient of variation), a measure of the repeatability, 

ranged from 3.3% to 27.3% for E. coli and from 2.5% to 5.1% for TC for the six samples 

tested, while the overall precision (coefficient of variation), a measure of reproducibility, 

ranged from 8.6% to 40.5% and from 6.9% to 27.7%, respectively. These values are 

based on log10-transformed data (Reference 16.5). 

13.6.2 Table 1 contains the statistical summary of the collaborative study (Reference 16.9) 

results. 

14.0 Pollution Prevention 

14.1 Pollution prevention is any technique that reduces or eliminates the quantity or toxicity of waste 

at the point of generation. It is the environmental management tool preferred over waste disposal 

or recycling. When feasible, laboratory staff should use a pollution prevention technique, such as 

preparation of the smallest practical volumes of reagents, standards, and media or downsizing of 

the test units in a method. 

14.2 The laboratory staff should also review the procurement and use of equipment and supplies for 

other ways to reduce waste and prevent pollution. Recycling should be considered whenever 

practical. 

15.0 Waste Management 

15.1 The Environmental Protection Agency requires that laboratory waste management practices be 

consistent with all applicable rules and regulations. The Agency urges laboratories to protect the 

air, water, and land by minimizing and controlling releases from hoods and bench operations, 

complying with the letter and spirit of sewer discharge permits and regulations and by complying 

with solid and hazardous waste regulations, particularly the hazardous waste identification rules 

and land disposal restrictions. All infectious wastes should be autoclaved before disposal. 

9 September 2002 
Method 1604 

16.0 References 

16.1 American Chemical Society. 1981. Reagent Chemicals. In American Chemical Society 

Specifications, 6th edition. American Chemical Society, Washington, D.C. For suggestions on 

the testing of reagents not listed by the American Chemical Society, see Analar Standards for 

Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K. and the United States Pharmacopeia. 

16.2 American Public Health Association. 1992. Standard Methods for the Examination of Water and 

Wastewater, 18th edition. American Public Health Association, Washington, D.C. 

16.3 American Society for Testing and Materials. 1993. Standard Specification for Reagent Water, 

Designation D1193-91, p. 45-47. In 1993 Annual Book of ASTM Standards: Water and 

Environmental Technology, Volume 11.01. American Society for Testing and Materials, 

Philadelphia, PA. 

16.4 American Society for Testing and Materials. 1994. Standard Practice for Determination of 

Precision and Bias of Applicable Methods of Committee D-19 on Water, Designation D 2777-86, 

p. 31-44. In 1994 Annual Book of ASTM Standards, Section 11: Water and Environmental 

Technology, Volume 11.01. American Society for Testing and Materials, Philadelphia, PA. 

16.5 Association of Official Analytical Chemists. 1989. Guidelines for Collaborative Study 

Procedure to Validate Characteristics of a Method of Analysis. Journal of the Association of 

Official Analytical Chemists 72 (4): 694-704. 

16.6 Bordner, R., J. Winter, and P. Scarpino (ed). 1978. Microbiological Methods for Monitoring 

the Environment: Water and Wastes. EPA-600/8-78-017, Environmental Monitoring and 

Support Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH. 

16.7 Brenner, K.P., and C.C. Rankin. 1990. New Screening Test to Determine the Acceptability of 

0.45-μm Membrane Filters for Analysis of Water. Applied and Environmental Microbiology 56: 

54-64. 

16.8 Brenner, K.P., and C.C. Rankin, Y.R. Roybal, G.N. Stelma, Jr., P.V. Scarpino, and A.P. 

Dufour. 1993. New Medium for the Simultaneous Detection of Total Coliforms and Escherichia 

coli in Water. Applied and Environmental Microbiology 59: 3534-3544. 

16.9 Brenner, K.P., C.C. Rankin, and M. Sivaganesan. 1996. Interlaboratory Evaluation of MI Agar 

and the U.S. Environmental Protection Agency-Approved Membrane Filter Method for the 

Recovery of Total Coliforms and Escherichia coli from Drinking Water. Journal of 

Microbiological Methods 27: 111-119. 

16.10 Brenner, K.P., C.C. Rankin, M. Sivaganesan, and P.V. Scarpino. 1996. Comparison of the 

Recoveries of Escherichia coli and Total Coliforms from Drinking Water by the MI Agar Method 

and the U.S. Environmental Protection Agency-Approved Membrane Filter Method. Applied and 

Environmental Microbiology 62 (1): 203-208. 

16.11 Buntel, C.J. 1995. E. coli $-Glucuronidase (GUS) as a Marker for Recombinant Vaccinia 

Viruses. BioTechniques 19 (3); 352-353. 

16.12 Federal Register. 1985. National Primary Drinking Water Regulations; Synthetic Organic 

Chemicals, Inorganic Chemicals and Microorganisms; Proposed Rule. Federal Register 

50: 46936-47022. 

16.13 Federal Register. 1994. National Primary and Secondary Drinking Water Regulations: 

Analytical Methods for Regulated Drinking Water Contaminants; Final Rule. Federal Register 

59: 62456-62471. 

September 2002 10 
Method 1604 

16.14 Federal Register. 1999. National Primary and Secondary Drinking Water Regulations: 

Analytical Methods for Chemical and Microbiological Contaminants and Revisions to Laboratory 

Certification Requirements; Final Rule. Federal Register 64: 67450-67467. 

16.15 U.S. Environmental Protection Agency. 1992. Manual for the Certification of Laboratories 

Analyzing Drinking Water: Criteria and Procedures, Quality Assurance, Third Edition. 

EPA-814B-92-002, Office of Ground Water and Drinking Water, Technical Support Division, 

U.S. Environmental Protection Agency, Cincinnati, OH. 

11 September 2002 
Method 1604 

17.0 Tables and Figures 

Table 1. Statistical Summary of the Collaborative Study Results1 

E. coli 

Target Sample Count _ RSDR

Organism Number Category Initial Final Sr

5 RSDr6 

P7 SR

8 RSDR9 RSDr (Range)2 n3 n4 (%) (%) Ratio 

Escherichia 

coli 1 Low 63 63 0.17 27.3 0.64 0.26 40.5 1.49 

2 

(# 10) 

63 63 0.21 25.0 0.84 0.33 39.0 1.56 

3 Medium 63 63 0.10 7.9 1.27 0.15 12.1 1.52 

4 (11-30) 63 60 0.07 5.6 1.32 0.12 9.2 1.65 

5 High 

(> 30) 

63 60 0.06 3.3 1.87 0.16 8.6 2.62 

6 63 63 0.09 4.3 1.99 0.25 12.6 2.91 

Total 

Coliforms 1 Low 63 63 0.10 4.3 2.35 0.62 26.4 6.11 

2 

(# 10) 

63 63 0.09 3.8 2.31 0.64 27.7 7.25 

3 Medium 63 63 0.11 5.1 2.17 0.47 21.8 4.28 

4 (11-30) 63 57 0.10 3.3 3.07 0.21 6.9 2.08 

5 High 63 63 0.15 4.8 3.10 0.43 14.0 2.96 

6 (> 30) 63 63 0.08 2.5 3.14 0.46 14.7 5.97 

1

 The values are based on log10 transformed data (Reference 16.5). 

2

 The samples were grouped by their E. coli count on MI agar into the following categories: 

Low (# 10 E. coli / 100 mL, samples 1 and 2), 

Medium (11-30 E. coli / 100 mL, samples 3 and 4), and 

High (> 30 E. coli / 100 mL, samples 5 and 6). 

3

 These values are based on triplicate analyses by each laboratory. The reference laboratory analyzed 

three sets of samples: the initial and final samples prepared and a sample shipped along with the other 18 

lab samples. 

4 These values were obtained after removing outliers by the AOAC procedure (Reference 16.5). 

5

 Sr, Single Operator Standard Deviation, a measure of repeatability. 

6

 RSDr, Single Operator Relative Standard Deviation (Coefficient of Variance), a measure of 

repeatability. 

_7 P, The mean of the replicate analyses for all laboratories. 

8

 SR, Overall Standard Deviation, a measure of reproducibility. 

9

 RSDR, Overall Relative Standard Deviation (Coefficient of Variation), a measure of reproducibility. 

September 2002 12 
Method 1604 

Figure 1. This photograph shows Escherichia coli (blue/green fluorescence) and total coliforms 

other than E. coli (blue/white fluorescence) on MI agar under longwave UV light (366 

nm). The sample used was a wastewater-spiked Cincinnati, Ohio tap water. 

Figure 2. These photographs show Escherichia coli and total coliforms from cistern water on MI 

agar. The confluent plate was photographed under different lighting: ambient light on the 

left, and longwave UV light (366 nm) on the right. Under ambient light, E. coli are blue, 

and total coliforms other than E. coli and non-coliforms are their natural color. Under 

longwave UV light, all total coliforms, including E. coli, are fluorescent, and noncoliforms are non-fluorescent (i.e., they are not visible). 

13 September 2002 
Method 1604 

Figure 3. This photograph shows that Escherichia coli (blue/green fluorescence) and total 

coliforms other than E. coli (blue/white fluorescence) can easily be detected on MI agar 

plates from samples with high turbidity levels. The sample used was surface waterspiked Cincinnati, Ohio tap water. 

September 2002 14