Viable but non culturable state and expression of pathogenic genes of Escherichia coli O157:H7 in salted silver carp

Abstract

AbstractMany bacteria including Escherichia coli can enter into the viable but non‐culturable (VBNC) state under unfavorable condition. This study investigated the fate of E. coli O157:H7 under high salinity stress in salted silver carp. E. coli O157:H7 was inoculated in distilled water and fish meat under 0, 10, and 30% NaCl at room temperature. The culturability of bacteria was investigated using culture‐based colony counting method. Viability and expression of pathogenic genes of E. coli O157:H7 were evaluated using reverse transcription polymerase chain reaction (RT‐PCR) of 16S rRNA, stx1, stx2, eae, and hly genes. The bacteria kept their culturability in both water microcosms and fish meat without salinity stress, however, bacterial culturabillity was lost under salinity of 10 and 30% in water microcosms on day 4 and in fish meat under salinity of 10% and 30%, respectively, on day 9 and 5. RT‐PCR showed positive expression of 16S rRNA in both culturable and non‐culturable bacteria indicating the entering of E. coli O157:H7 into the VBNC state under salinity stress. Moreover, VBNC E. coli O157:H7 kept the expression of its pathogenesis genes. So, E. coli O157: H7 in salted silver carp should be considered as a threat to public health and food safety.