Materials and methods
2.1. Test organisms and spore production
Three strains of C. perfringens, NCTC 8238 (Hobbs
serotype 2), NCTC 8239 (Hobbs serotype 3), and NCTC
10240 (Hobbs serotype 13), obtained from our culture
collection, were used in this study. The spores were produced
in a modified formulation of Duncan and Strong sporulation
medium as previously described (Juneja et al., 1993). After the
spore crop of each strain had been washed twice and resuspended
in sterile distilled water, the spore suspensions were
stored at 4 °C. Spores of individual strains at equal numbers
were then mixed to prepare a cocktail. This composite of spore
strains was not heat-shocked prior to use.