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BBL™ Modified mTEC Agar is a selective culture medium used for the chromogenic detection and enumeration of thermotolerant Escherichia coli in water by the membrane filtration technique. It conforms with U.S. Environmental Protection Agency (USEPA) Approved Method 1603: Escherichia coli (E. coli) in Water by Membrane Filtration Using Modified membrane-Thermotolerant Escherichia coli Agar (modified mTEC).

mTEC is an acronym for "membrane Thermotolerant E. coli." E. coli is widely used as an indicator of fecal pollution in water. This organism has a high correlation with gastroenteritis in fresh water environments.¹ In 1986, the USEPA recommended that E. coli be used as a bacterial water quality indicator to monitor recreational waters.²

Many procedures have been developed for enumerating E. coli based on its ability to grow at elevated temperatures and produce indole from tryptophan.^3,4 The determination of indole production in conjunction with the most-probable-number procedure often requires the use of another medium and additional incubation time.

Dufour developed a membrane filtration procedure using mTEC agar for the rapid enumeration of E. coli.^5,6 This alternative two-step test procedure quantified E. coli within 24 hours without requiring subculture and identification of isolates. However, the membrane filter had to be transferred after the initial incubation at an elevated temperature to a urea substrate/phenol red-saturated pad.

The modified mTEC method was developed by the USEPA in 1998^7,8 as a single-step procedure that does not require the transfer of the membrane filter to another substrate. The modified medium contains the chromogen 5-bromo-6-chloro-3-indolyl-ß-D-glucuronide. This chromogen is catabolized to glucuronic acid by E. coli strains that produce the enzyme ß-D-glucuronidase to form red- or magenta-colored colonies, enabling confirmatory identification of E. coli in 24 hours. Red or magenta colonies can be verified as E. coli in instances where required in evidence gathering or for performing quality control for the initial use of this test.⁸ As referenced in USEPA method 1603, the false-positive rate is <1% and the false-negative rate is 4% from a variety of environmental water samples.⁸

This medium is recommended for testing the presence of E. coli as an indicator organism for fecal contamination in fresh recreational water. This allows for a wide range of sample volumes or dilutions to be analyzed by membrane filtration for the detection and enumeration of E. coli levels in water.

1. Examine plates for signs of deterioration.

2. Check performance by inoculating a representative sample of plates with pure cultures of stable control organisms that give known, desired reactions. Inoculate and incubate the plates at 35°C ± 0.5 for 2 h. Transfer plates and incubate at 44.5 ± 0.2°C for 22-24 h. Count all red or magenta colonies

3. Determine the pH potentiometrically at room temperature for adherence to the specification of 7.3 ± 0.2.

4. Incubate uninoculated representative plates at 35 ± 2°C for 72 h and examine for microbial contamination.

For Laboratory Use.

Observe aseptic techniques and established precautions against microbiological hazards throughout all procedures. After use, prepared plates and other contaminated materials must be sterilized by autoclaving.