Membrane filtration enumeration of faecal clostridia and clostridium perfringens in water

The use of egg yolk-free tryptose-sulphite-cycloserine (TSC) agar for the membrane filtration enumeration of Clostridium perfringens was evaluated using domestic sewage effluents and polluted surface waters. The medium recovered higher numbers of C. perfringens than a medium containing polymixin (mCP). Overlaying the membrane with TSC or cycloserine-free TSC did not improve recoveries. Supplementation of the medium with 50 mg l −1 neomycin sulphate resulted in significantly lower recoveries of C. perfringens. Comparison of two commercial formulations of TSC showed no difference in recoveries. A two tube confirmation procedure based on motility, nitrate reduction, lactose fermentation and gelatin liquefaction was found to be reliable to confirm C. perfringens from TSC plates. Although not as specific as mCP for the enumeration of C. perfringens TSC aappeared to be selective for sulphite reducing clostridia of predominantly faecal or urino-genital origin. A concept of faecal clostridia and C. perfringens (based on enumeration on TSC agar) analogous to that of faecal coliforms and E. coli is briefly discussed.