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Analytical Methods

Modified mTEC agar method for Escherichia coli: U.S. Environmental Protection Agency Method 1603. Updated October 2007

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:
Modified mTEC agar plates are incubated at 35C for 2 hours followed by incubation at 44.5C for 22 hours.  The modified mTEC agar contains selective and differential agents. 
Sodium lauryl sulfate and sodium desoxycholate are selective agents that inhibit Gram + cocci and endospore-forming bacteria.  The modified mTEC agar contains the differential agent, 5-bromo-6-chloro-3-indolyl-b-D-glucuronide, which is catabolized to glucuronic acid and a red- or magenta-colored compound by E. coli that produce the enzyme b-D-glucuronidase.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)) or from Fisher Scientific (800/766-7000, Cat B14880 (500 g)).

Pre-poured plates can be purchased in lots of 20 plates from Fisher Scientific (Cat B15044) or VWR (Cat 900006-314).  Other quantities and plate sizes are available from these manufacturers. 

Use phosphate buffered dilution water and 0.45 mm membrane filters.  Buffer can be purchased from Hardy Diagnostics (800/266-2222, 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, 2006, Method 1603—Escherichia coli in water by membrane filtration using modified membrane-thermotolerant Escherichia coli agar: Washington, D.C., EPA 821-R-06-011, 42 p.

NWIS PARAMETER CODES:
90902 E. coli on modified mTEC agar, colonies per 100 mL