Analytical Methods

mFC agar method for fecal coliforms. Updated January 2007

The mFC agar method is a one-step membrane-filtration method for enumeration of fecal coliforms.  See Britton and Greeson (1987) for a step-by-step description of the method.  This method can be done in the field or laboratory.

THEORY:
Agar plates are incubated at 44.5°C for 22-24 hours. The mFC agar contains selective and differential agents.  Rosolic acid inhibits bacterial growth in general, except for fecal coliforms.  Bile salts inhibit non-enteric bacteria.  Aniline blue indicates the ability of fecal coliforms to ferment lactose to acid that causes a pH change in the medium.

Lactose utilization (blue color) is the basis for identification of fecal coliforms.

USE:
The mFC method can be used for monitoring all types of water; however, it is an old method that is slowly being replaced by newer methods and alternative indicators in state regulatory programs.  For coastal recreational waters, E. coli is the required indicator for freshwaters and E. coli or enterococci are the required indicators for marine waters; fecal coliforms are no longer used (U.S. Environmental Protection Agency, 2004).  Fecal coliforms are still used to assess the sanitary quality of shellfish-growing waters and, in some states, for attainment of effluent permitting standards and inland recreational water-quality standards.  Under the Total Coliform Rule of the Surface Water Treatment Rule (USEPA, 1989), all total-coliform positive samples found in a community water system must be tested for E. coli or fecal coliforms.

We recommend that for new monitoring programs, E. coli be used instead of fecal coliforms, whenever possible.  Fecal coliforms may be from fecal or nonfecal sources.  E. coli is natural inhabitant of the gastrointestinal tract of warmblooded animals and is direct evidence of fecal contamination.   The mFC method, however, can be used for comparisons with historical data.  

MEDIA: 
The mFC medium is available commercially in the dehydrated form from Fisher Scientific (800/766-7000, Cat DF0677-15-5 (100 g) or DF0677-17-3 (500 g)).  Rosolic acid will also need to be purchased from Fisher Scientific (Cat DF3228-09-1 (pack of six 1-g aliquots) and dissolved in 2 N NaOH (Fisher Scientific, Cat AC34968-5000 (500 mL)). Follow the manufacturer’s instructions for media preparation.

Pre-poured plates can be purchased from Microbiology International (800/396-4276, Cat 215166 (30 plates)) or from Fisher Scientific (Cat B4392345 (10 plates)).  Rosolic acid is incorporated in the prepoured plates and does not have to be added.

Use phosphate buffered dilution water and 0.45 mm membrane filters (0.65 mm filters are still acceptable).  Buffer can be purchased from Hardy Diagnostics (800/266-2222, Cat D699 (99mL) or Cat U193 (500mL)).  See buffer preparation (Appendix M).

REFERENCES: 
Britton, L.J., and Greeson, P.E., eds., 1987, Methods for collection and analysis of aquatic biological and microbiological samples: U.S. Geological Survey Techniques of Water Resources Investigations, book 5, chap. A4,  p. 37-40.

U.S. Environmental Protection Agency, 1989, Drinking water—National Primary Drinking Water Regulations—total coliforms (including fecal coliforms and E. coli): Federal Register, vol. 54, no. 124, p. 27544.

U.S. Environmental Protection Agency, 2004, Final rule, water quality standards for coastal and Great Lakes recreation waters: Title 40, part 131, 67218 p.

NWIS PARAMETER CODES:
31616 Fecal coliforms on mFC agar at 44.5°C, colonies per 100 mL

31625 Fecal coliforms, 0.7 mm, colonies per 100 mL

Parameter code 31616 provides a better description of the method and is to be used for current work.