Factors Affecting Enterotoxin Production by Thermonuclease Positive Streptococcus faecium IF‐100 Isolated from an Infant Food

Among the different media tested for optimal production of enterotoxin by Streptococcus faecium IF‐100, trypticase soy broth was the best for maximal enterotixin production by Streptococcus faecium IF‐100 at 37°C after 8 hr incubation in agitated cultures. The pH optimum was 8.0. Although addition of 1% casamino acid enhanced enterotoxin production, yeast extract did not affect enterotoxin production appreciably. Dextrose, at 0.5%, was inhibitory towards enterotoxin production. Production of enterotoxin was also inhibited by addition of acridine orange, suggesting possible involvement of some extra chromsomal factor in the production of this metabolite in S. faecium IF‐100. A supplemented medium for maximum enterotoxin production is described.