378. The effect of penicillin on lactic streptococci

Abstract

Ten strains of ‘starter’ streptococci were found to be susceptible to penicillin. Streptococcus cremoris strains were markedly inhibited under the conditions employed by doses of 0·10 unit/ml. Str. lactis strains were not inhibited to the same degree unless 0·25–0·30 unit/ml. was present in the milk. These results would indicate that if penicillin is used extensively by farmers and the milk from treated quarters is included in the factory supply, difficulties may arise in cheese manufacture, especially when the more sensitive Str. cremoris strains are used as starter.