Centrifuge-washed spores were resuspended in 0.1 M citric buffer (pH 4.75 or 6.5) or 10 mM PBS (pH
7.4) to a concentration of approximately 5 × 106 spores/mL. Spores
were stored at −20 ◦C and used within 60 d. Spores of C. sporogenes (strains ATCC 3584 and 7955) were prepared following the procedures described for C. perfringens. The only modifications were
that C. sporogenes vegetative cells grown overnight in FTG medium
(0.3 mL) were inoculated into 10 mL DS sporulating medium and incubated for 3 to 5 d at 37 ◦C. FTG, DS, and TGY were used on the same day of preparation