Ohio District's Microbiology Laboratory

Escherichia coli, using the modified mTEC method

Updated May 2005

The modified mTEC agar method is a one-step membrane-filtration method for detection of Escherichia coli (E. coli). This method can be done in the field or laboratory.

THEORY: The first step is incubation of modified mTEC agar plates at 35°C for 2 hours followed by incubation at 44.5°C for 22 hours.  The modified mTEC agar contains selective and differential agents.  Sodium lauryl sulfate and sodium desoxycholate inhibit Gram + cocci and endospore-forming bacteria.  Detection of E. coli is based on the presence of the enzyme, b-D-glucuronidase, that most E. coli produce.  When E. coli are present, a chromagen in the medium, 5-bromo-6-chloro-3-indolyl-b-D-glucuronide, is catabolized to glucoronic acid and a red- or magenta-colored compound.  Unlike the original mTEC method, the modified mTEC does not require the transfer of the membrane filter to another substrate. 

USE:  The modified mTEC method is recommended for use in monitoring fresh, estuarine, and marine surface waters.  It was specifically developed to be used as a measure of recreational water quality.

MEDIA:  Dehydrated modified mTEC medium can be purchased from Government Scientific Source (800/248-8030, Cat 214884 (100g) or Cat 214880 (500g)).

Prepoured plates can be purchased from Microbiology International (800/EZ-MICRO).

Use phosphate buffered dilution water and 0.45 mm membrane filters.  Buffer can be purchased from Hardy Diagnostics (800/346-2766, Cat D699 (99mL) or Cat U193 (500mL)).  See buffer preparation (Appendix M).

REFERENCES: 

U.S. Environmental Protection Agency, 2000.  Improved enumeration methods for the recreational water quality indicators: Enterococci and Escherichia coli: Washington , D.C. , EPA/821/R-97/004 March 2000.

U.S. Environmental Protection Agency, 2002, Method 1603—Escherichia coli in water by membrane filtration using modified membrane-thermotolerant Escherichia coli agar: Washington , D.C. , EPA 821-R-02-23, 9 p.

These documents can be obtained at  http://www.epa.gov/nerlcwww/index.html

NWIS PARAMETER CODES:

90902 E. coli on modified mTEC agar, colonies per 100 mL