PERFRINGENS (TSC) SELECT SUPP.1 X 10VIAL

Description
Perfringens Agar Base (TSC and SFP) is a nutrient medium to which egg yolk emulsion (SR0047) and the appropriate antibiotic supplement can be added, to make either Shahidi-Ferguson Perfringens (SFP)¹ Agar or Tryptose Sulphite Cycloserine (TSC)² Agar. An egg yolk free TSC Agar had been described^4,5 which has the advantage that smaller colonies are formed. This can simplify the counting of plates with high numbers of colonies.

Higher counts have been demonstrated by using it with a pour-plate technique. The differences were thought to be due to exposure of the Clostridium perfringens cells to high oxygen tension in the surface plating procedure⁴.

Shahidi-Ferguson Perfringens Agar is based on the formulation developed by Shahidi and Ferguson¹. The medium utilises kanamycin sulphate (12mg/l) and polymyxin B sulphate (30,000IU/l) as the selective agents, to give a high degree of selectivity and specificity for Clostridium perfringens. Tryptose Sulphite Cycloserine Agar was developed using the same basal medium as SFP Agar² but with 400mg/l of D-cycloserine as the selective agent. Sodium metabisulphite and ferric ammonium citrate are used as an indicator of sulphite reduction by Clostridium perfringens which produces black colonies in both media.

Trials³ have indicated that polymyxin B and kanamycin sulphate used in SFP Agar allow a greater recovery of both vegetative cells and spores of Clostridium perfringens than either polymyxin B and sulphadiazine used in Sulphite Polymyxin Sulphadiazine Agar, or neomycin used in Tryptone Sulphite Neomycin Agar. However, a greater number of non-specific colonies were found on SFP Agar.

In another study², Serratia marcescens and Streptococcus lactis were the only facultative anaerobes to grow on TSC Agar, whereas SFP Agar also allowed the growth of Enterococcus, Proteus and Enterobacter strains. However, it also  allowed a slightly higher rate of recovery of Clostridium perfringens than TSC Agar. Both SFP Agar and TSC Agar permitted growth of other sulphite-reducing Clostridium species tested.

Some strains of Cl. perfringens may produce an opaque zone around the colony due to lecithinase activity, but this is not considered to be universal for all Clostridium perfringens strains after overnight incubation⁴, and both black, lecithinase positive and black, lecithinase negative colonies should be considered as presumptive Clostridium perfringens on TSC or SFP Agars and confirmatory tests carried out. Lecithinase positive, facultative anaerobes may grow on SFP Agar to produce completely opaque plates that mask the egg yolk reaction of Clostridium perfringens.