Ohio District's Microbiology laboratory

Fecal coliforms, using the mFC method

Updated May 2005

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 waters. Because fecal coliforms may be from nonfecal sources, however, we recommend the mFC method be used in new monitoring programs for comparisons with historical data only.  Instead, for new studies, E. coli should routinely be tested. E. coli is natural inhabitant of the gastrointestinal tract of warm-blooded animals and is direct evidence of fecal contamination. 

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.  For recreational waters, the USEPA recommends that E. coli be used in place of monitoring for fecal coliforms (USEPA, 1986).  Because many states were slow to adopt E. coli in state recreational water-quality standards, the Beaches Environmental Assessment, Closure, and Health Act of 1999 was proposed to mandate that E. coli be used for monitoring all freshwater recreational waters (see http://www.epa.gov/OST/beaches/technical.html).  Thus, although fecal coliforms are still included in standards for drinking and recreational waters, the switch over to E. coli appears to be inevitable. 

MEDIA:  The mFC medium is available commercially in the dehydrated form from Fisher Scientific (800/766-7000, Cat DF0677-15-5).  Rosalic acid will also need to be purchased from Fisher Scientific (Cat DF3228-09-1). Instructions for media preparation can be found in Myers and Wilde (2003) page FIB-59.

Prepoured plates can be purchased from Hardy Diagnostics (800/266-2222, Cat G126). Rosalic acid is incorporated in the prepoured plates and does not have to be added.

Use phosphate buffered dilution water and 0.65 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: 

Britton, L.J., and Greeson, P.E., eds., 1989, 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.

Myers, D.N., and Wilde, F.D., eds., 2003, National field manual for the collection of water-quality data—Biological indicators: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A7, 158 p.

U.S. Environmental Protection Agency, 1986, Bacteriological ambient water-quality criteria: Federal Register, v. 51, no. 45. p. 8012-8016.

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.

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.