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Effect of Incubation Temperatures on the Retention of Bacteriophage by a Culture of Streptococcus Lactis¹

Dairy Department, Purdue University, Lafayette, Indiana

ABSTRACT

A study was made of the coagulation times and bacteriophage titers of a culture of S. lactis, without and with added bacteriophage, using incubation temperatures of 21, 26 and 21, and 37° C.

A culture of S. lactis inoculated once with bacteriophage active against the culture required 132 transfers before the culture became free of bacteriophage when incubation was carried out at 21° C. When the culture was inoculated once with bacteriophage and incubated at 26° C. for nine transfers and then at 21° C, it did not contain bacteriophage after 34 transfers. The same cultureinoculated once with bacteriophage and propagated at 37° C. did not contain baeteriophage after 10 transfers.

Cultures of S. lactis inoculated with bacteriophage active against the cultures produced acid rather rapidly after a few transfers, even though baeteriophage was present in the cultures.

Secondary-growth organisms resulting from the action of bacteriophage on a culture of S. lactis appeared to be similar to the parent culture in morphology, colony characteristics and in their ability to ferment sugars.

Secondary-growth organisms were resistant to the bacteriophage type causing incomplete lysis of the parent culture but were sensitive to at least one other bacteriophage type.

Secondary-growth organisms propagated in the presence of bacteriophage active against the parent culture were not sensitive to another bacteriophage type until the original bacteriophage had disappeared from the culture after repeated transfer.

¹ Published with the approval of the Director of the Purdue Agricultural Experiment Station as Journal Series Paper no. 447.