Studies on the Susceptibility of Certain Cheese Cultures to the Action of Bacteriophage

Summary During an outbreak of slow acid production in cheese manufacture due to bacteriophage, an attempt was made to control the difficulty by the use of cultures that were not sensitive to the bacteriophage types responsible for the outbreak. These cultures had been carried in the regular culture collection. The five cultures selected for study developed sensitivity to bacteriophage after being used in the manufacture of cheese for 1 or 2 days. One culture (W4) isolated from sour cream produced acid rapidly in cheese manufacture for approximately 3 months before it developed sensitivity toward bacteriophage. Culture Ml, also isolated from sour cream, produced acid satisfactorily for more than 6 months; at the end of this period it was not sensitive to bacteriophage. Multiple-strain cheese cultures may fail as completely as single-strain cultures to produce acid. Four distinct types of bacteriophage were recovered from a sample of whey taken from a vat in which a multiple-strain culture was used and in which there had been complete cessation of acid production. Ten bacteriophage types which are active against one or more of fifteen cultures of S. lactis isolated from a multiple-strain cheese culture were isolated from various plants experiencing difficulty with slow acid production. The bacteriophage types were differentiated by means of their bacteriophage activity pattern.