Positive results can be obtained most rapidly by using penassay seed agar or equivalent in not over 6 ml. amounts per plate, preincubating for one hour, using 0.5″ discs and incubating at 37°C. after “spotting.” Lower incubation temperatures prolong the time required for zone formation. Heat-shocking of the spore suspension also generally hastens growth. Refrigeration of poured plates before use is not necessary, but with penassay seed agar has little delaying effect until after 5 days.
1Contribution No. 36 from the Dairy Technology Research Institute.