M 7 Hr FC Agar

Principle and Interpretation

M7 Hr FC Agar is a modified method of Van Donsel et al (1) and Reasoner et al (2), which is recommended by APHA (3) for the examination of water and wastewater for the presence of faecal coliforms by the membrane filter technique. This medium has an advantage over other media to yield results in 7 hours that are generally comparable to those obtained by the standard coliform method. Thus this medium is accepted for assessment of the sanitary quality of water during emergencies involving water treatment plant failure or line breaks in a distribution network. It is reliable and has sensitivity levels equal to those of the standard tests routinely used.

Biopeptone and yeast extract provide nutritional requirement to a wide variety of organisms. Lactose and mannitol are energy sources and sodium chloride maintains osmotic equilibrium of the medium. Sodium lauryl sulphate and sodium deoxycholate help to restrict the gram-positive and gram-negative bacterial flora present in water. Bromocresol purple and phenol red help as indicators in the detection of organisms. This is a solid culture medium for the rapid detection of faecal coliforms by membrane filtration method.

After filtering a suitable or desired volume of water, the membrane is placed on the surface of plate and then incubated at 41.5°C for 7 hours. Faecal coliform form yellow colonies, indicating lactose fermentation.

MF technique has certain limitations, particularly when testing waters with high turbidity or non-coliform (background) bacteria. For such waters or when the membrane filter technique has not been used previously, it is desirable to carry out parallel tests with the multiple tube fermentation technique to determine applicability and comparability.