Heat Resistance of Some Selected Toxigenic Enterococci in Milk and Other Suspending Media

Streptococcus faecium IF-100, S. faecalis var. zymogenes RCM-29 (both toxigenic) and S. faecalis var. liquefaciens N.P. were subjected to 50–70°C in reconstituted nonfat dry cow's milk (NFDCM), spray-dried infant food (RIF), full cream buffaloe's milk (FCBM), normal saline and brain heart infusion (BHI) broth for different periods of time. S. faecium IF-100 was the most heat resistant in all the heating media as evidenced by high D values, i.e., 8.5, 8.5, and 6.5 min in RIF, FCBM and NFDCM, respectively, even at 70°C. The corresponding D values in respect to S. faecalis var. liquefaciens were 3.5 min each in the three menstrua. However, the heat resistance of the test cultures was the least in normal saline (D values ranging from 1 min (RCM-39) to 2.5 min (IF-100). The variations in D values of the 3 enterococci were statistically significant at 1%.

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