It is not as specific an indicator of fecal contamination, but is a useful screening test . Both fecal and nonfecal coliforms will grow and produce metallic green colonies . Coliforms would indicate the possibility of fecal contamination of the water . Both of these tests use the micropore membrane filter method. The water passes through and the bacteria are trapped on the surface of the filter.
Colonies then form on the filter.
By counting the number of colonies and knowing the volume of water sample used, the number of fecal coliforms or total coliforms per ml of water can be determined. Take three 50mm petri plates and aseptically place a sterile pad in the bottom of each. Label the plates 0.1ml, 1.0ml, and 10.0ml. Using a 10ml pipette , add 2.0ml of M-coliform broth to each pad. Secure the funnel to the filter set-up. 5.