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 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 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