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

Many 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 , stx 1 , stx 2 , 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.