Survival of Escherichia coli O157:H7 during Fermentation of Apple Cider

Abstract

Survival of Escherichia coli O157:H7 in fermenting and nonfermenting fresh apple cider was determined. Populations of E. coli O157:H7 were reduced from 6.4 log CFU/ml to undetectable levels (detection limit of 0.5 log CFU/ml) in fermenting cider after 3 days at 20°C and from 6.5 log CFU/ml to 2.9 log CFU/m1 after 10 days at 20°C in nonfermenting cider. After 1 day of incubation, recovery of E. coli O157:H7 from fermenting and nonfermenting cider was statistically (P < 0.01) lower on sorbitol MacConkey agar than on tryptone soya agar supplemented with cycloheximide. These results suggest that substantial portions of the surviving E. coli O157:H7 populations were sublethally injured by cider components (i.e., acid and ethanol). The pH of fermenting cider was not significantly different (P > 0.05) from that of nonfermenting cider throughout the 10-day test period. Final ethanol concentrations in fermenting cider reached 6.01% (vol/vol) after 10 days at 20°C. Inactivation of E. coli O157:H7 in fermenting cider is attributed to the combined effects of pH and ethanol. Results of this study indicate that E. coli O157:H7 is capable of survival in fresh apple cider at 20°C, while alcoholic fermentation of fresh cider is an effective means of destroying this pathogen.