Fecal Coliforms Broth Base (m-FC)

Fecal coliforms are differentiated from other coliforms from environmental sources by their ability to grow at 44.5 ± 0.5 °C.

Proteose and tryptose provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group, essential for bacterial growth. Lactose is the fermentable carbohydrate as a carbon and energy source. Bile salts and aniline blue inhibit growth of Gram-positive bacteria. Sodium chloride maintains the osmotic balance. Aniline blue and rosolic acid, which is provided by the supplement, are the differential indicators. Bacteriological agar is the solidifying agent.

Preparation

Suspend 37.1 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Cool to 45-50 °C and aseptically add 2 vials of Fecal Coliforms Supplement (LC-6023), each vial for 500 mL of the medium, previously reconstituted in 5 mL of 1% 0.2 N NaOH solution. Boil for one minute until complete dissolution. Cool to 45-50 °C and pour 2 mL of the broth medium onto each sterile absorbent pad placed on Petri dishes. DO NOT AUTOCLAVE.

Instructions for use

Membrane filtration method:

1. Place the membrane filter, which the sample has been filtered through, on the upper part of the pad saturated with the medium in the Petri dish.
2. Incubate the plates for 24 ± 2 hours, one batch as control at 35 ± 2 °C, and the rest at 44.5 ± 0.5 °C.
3. Observe the coliforms and count the colonies.

The differential indicator system (aniline blue and rosolic acid) gives a blue color to the colonies of fecal coliforms, while the rest of the microorganisms will become pinkish colored.

• Geldreich, Clark and Kabler, 1963. USPHS, HEW. Personal Communication.
• Geldreich, Clark, Huff and Bert, 1965. Journal of American Water Works Association, 57:208.