Acid adaptation effect on survival of Escherichia coli O157:H7 in fermented milk products
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The growth and survival of acid-adapted and nonadapted Escherichia coli O157:H7 were determined in strained, set-type, and synbiotic yoghurt and kefir. Acid-adapted or nonadapted E. coli O157: H7 were inoculated into the synbiotic and set-type yoghurt before and after the fermentation process. Survival of the inoculated E. coli O157: H7 in these products was examined during storage at 4 degrees C. Acid adaptation enhanced the survival of E. coli O157: H7 in kefir and strained yoghurt. Acid adaptation also enhanced the survival of E. coli O157: H7 in set-type yoghurt, which was inoculated after the fermentation process; however, acid-adapted cell inoculation before fermentation did not enhance survival. These observations support the theory that acid adaptation is an important survival mechanism enabling E. coli O157: H7 to persist in fermented dairy products.