FACTORS INVOLVED IN THE ISOLATION OF CLOSTRIDIUM PERFRIHGEHS1

Abstract

Quantitative isolation of Clostridium perfringens requires that dilutions be made anaerobically; that a relatively complete medium be used; that incubation be under strictly anaerobic conditions or that the medium contain an active reducing agent. Roll tubes, pour plates, or surface-inoculated plates may be used if other conditions are suitable. Selective agents inhibitory for other bacteria but only slightly for C. perfringens include sulfite, neomycin, polymyxin, sulfadiazine, kanamycin, and cycloserine. Several selective media utilizing such agents have been devised but none inhibits all other bacteria without some inhibition of C. perfringens, SFP medium ( Shahidi, Ferguson, perfringens medium) is the least inhibitory both for other bacteria and for C. perfringens. TSN medium (tryptone, sulfite, neomycin) is most inhibitory for other bacteria, but is also somewhat inhibitory for C. perfringens. SPS medium (sulfite, polymyxin, sulfadiazine) is intermediate in these properties. The number of living C. perfringens cells in food or other material can also be estimated by using the MPN technique and incubating at 45 C. If the C. perfringens in the specimen have been killed by freezing or cold storage, the numbers originally present may be estimated by determining the amount of phospholipase C that is present.