Survival of O157 and non-O157 shiga toxin-producing Escherichia coli in Korean style kimchi.

ABSTRACT

Korean style kimchi contaminated with Shiga toxin-producing Escherichia coli (STEC) O157H7 was the cause of an outbreak in Canada from December 2021 to January 2022. To determine if this STEC O157H7 has greater potential for survival in kimchi than other STEC, the outbreak strain and six other STEC strains (O26H11, O91H21, O103H2, O121H19, and two O157H7) were inoculated individually at 6 to 6.5 log CFU/g into commercially sourced kimchi and incubation at 4 °C. At intervals of seven days inoculated and control kimchi was plated onto MacConkey agar to enumerate lactose utilising bacteria. The colony counts were interpreted as enumerating the inoculated STEC, since no colonies were observed on MacConkey agar plated with uninoculated kimchi. Over eight weeks of incubation the pH was stable at 4.10 to 4.05 and the STEC strains declined by 0.7-1.0 log, with a median reduction of 0.9 log. The linear rate of reduction of kimchi outbreak STEC O157H7 was -0.4 log per 30 days (Slope Uncertainty 0.05), which was not significantly different from the other O157 and nonO157 STEC strains (P = 0.091). These results indicate that the outbreak was not due to the presence of strain better adapted to survival in kimchi than other STEC, and that STEC can persist in refrigerated Korean style kimchi with a minimal decline over the shelf-life of the product.