EVALUATION OF C-EC-AGAR, A MODIFIED MFC-AGAR FOR THE SIMULTANEOUS ENUMERATION OF FECAL-COLIFORMS AND ESCHERICHIA-COLI IN WATER SAMPLES

A new medium, C-EC-agar (Biolife, Milan, Italy), was evaluated for the simultaneous enumeration by membrane filtration of faecal coliforms a nd Escherichia coli in water. The medium is a modification of m-faecal coliform agar, from which the aniline blue and lactose have been omit ted and 4-methylumbelliferyl-beta-D-glucuronide, -bromo-4-chloro-3-ind olyl-beta-D-galactopyranoside and isopropyl-beta-D-thiogalactoside add ed. At 44 degrees C E. coli gives blue-green colonies that fluoresce u nder u.v.-light (366 nm) and give a reddish-violet colour when Kovac's reagent is placed on the membrane. Under similar conditions, faecal c oliform colonies do not fluoresce. To increase recovery on the medium, repair of sub-lethally injured cells by a 4-h incubation at 37 degree s C on tryptic soy agar is recommended.