Survival of Escherichia coli O157:H7 during fermentation of apple cider

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 degrees C and from 6.5 log CFU/ml to 2.9 log CFU/ml after 10 days at 20 degrees 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 0 days at 20 degrees 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 degrees C, while alcoholic fermentation of fresh cider is an effective means of destroying this pathogen