HEAT RESISTANCE OF ENTEROCOCCI1,2

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Abstract
Fifty enterococcus cultures were exposed to temperatures of 62.8 and 71.1 C for 30 min and 71.7 C for 15 sec in skimmilk containing approximately 10 million cells/mi. Streptococcus durans was most heat resistant, although no culture survived 71.1 C for 30 min. Additional milk solids and fat did not provide protection from destruction by heat. In skimmilk, at population levels of approximately 100/ml, the cultures survived heat treatments of 71.7, 76.7, and 82.2 C for 16 sec by 55.2, 46.4., and 32.5%, respectively. After pasteurization at 62.8 C for 30 min, only 8 of 426 commercial milk samples had detectable enterococci. These 8 samples contained from 1 to 30 enterococci/ml. When 55 of these more heat-resistant cultures were again laboratory pasteurized, 32 remained viable. Only 8 of these 32 cultures showed numerical increase when stored at 5 to 8 C for 7 days after laboratory pasteurization. Before enterococci can be used as indices of bacterial quality in dairy products, their presence or absence must be related to the specific heat treatments given dairy products.

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