Enumeration of food-borne Clostridium perfringens in egg yolk-free tryptose-sulfite-cycloserine agar.

The SFP (Shahidi-Ferguson perfringens), TSC (tryptose-sulfite-cycloserine), EY (egg yolk)-free TSC, and OPSP (oleandomycin-polymyxin-sulfadiazine perfringens) agars have been tested for their suitability to enumerate Clostridium perfringens in naturally contaminated foods. Complete recoveries of C. perfringens were obtained in each of the four media, but only the TSC and EY-free TSC agars were sufficiently selective to ensure subsequent confirmatory tests without interference from facultative anaerobes. Because of some disadvantages associated with the use of egg yolk, EY-free TSC agar is recommended for enumeration of C. perfringens in foods. Several conditions for convenient shipment of foods and C. perfringens isolates with minimum loss of viability have been tested. The highest viable counts were preserved when foods were mixed 1:1 (wt/vol) with 20% glycerol and kept in a container with dry ice. Isolated C. perfringens strains remained viable for at least 2 weeks at ambient temperatures on blood agar slopes with a 2% agar overlay in screw-cap culture tubes.