Heat Resistance and Other Characteristics of Deoxyribonuclease Positive Enterococci Isolated from Milk and Milk Products

Abstract

Out of 224 deoxyribonulcease (DNase) positive enterococci recovered from dairy products, 21.9% survived pasteurization. Among the latter, 26 exhibited thermonuclease activity and 14 were hemolytic. Enterotoxigenic activity in rabbit ileal loops was exhibited by 13 strains, whereas 14 strains were pathogenic to mice. Resistance to penicillin and streptomycin was shown by 5 1 and 47 strains, respectively. There appears to be a positive relationship between heat resistance, thermonuclease activity, enterocin production by these organisms and their resistance to penicillin and streptomycin. As many as 37 heat resistant strains were recovered from samples of nonfat dry cow's milk, infant foods and from sweetened condensed milk. The predominant heat resistant strains were identified as Streptococcus faecalis var. faecalis., Streptococcus faecium and Streptococcus faecalis var zymogenes.