University of Guilan Caspian Journal of Environmental Sciences 1735-3033 19 4 2021 10 01 The change in heat inactivation of Escherichia coli O157:H7 after entering into the viable but non-culturable state in salted fish, Hypophthalmichthys molitrix 629 637 5136 10.22124/cjes.2021.5136 EN Mohammad Khezri Department of Seafood Science, Faculty of Marine Sciences, Tarbiat Modares University, Noor, Iran Masoud Rezaei Department of Seafood Science, Faculty of Marine Sciences, Tarbiat Modares University, Noor, Iran Ashraf Mohabbati Mobarez Department of Bacteriology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Mehdi Zolfaghari Fisheries Department, Agriculture and Natural Resource University of Gorgan, Gorgan, Iran Journal Article 2021 10 30 Many species of non-sporulating bacteria including Escherichia coli can enter into a viable but non-culturable (VBNC) state under stress conditions. In this study, the change in thermal resistance of E. coli O157:H7 after entering into the VBNC state in salted silver carp, Hypophthalmichthys molitrix, was investigated. E. coli O157:H7 was inoculated on the fish control group (TF) and on those fish with 30% NaCl (TF + 30% NaCl) at room temperature. Culturability of bacteria was determined using routine culture and colony counting on Sorbitol MacConkey agar. When bacteria were non-cultivable, the RT-PCR of 16S rRNA gene (including direct extraction and purification of RNA, DNase I treatment for removing DNA contamination, cDNA synthesis and electrophoresis of PCR products of cDNA) was used to detect VBNC E. coli O157:H7. Also, cultivable and VBNC E. coli O157:H7 were individually heat-treated at 55, 62 and 70 °C for 5 min. The samples were cooled and after 24 h, the thermal resistance of bacteria was determined through viability detection using RT-PCR of 16S rRNA gene. The culturability of bacteria was kept in fish treatment but they were non-cultivable in fish under 30% NaCl after 5 days. The positive expression of 16S rRNA in all studied treatments indicated the entering of E. coli O157:H7 into the VBNC state in fish treatment under 30% NaCl. Moreover, the RT-PCR of 16S rRNA gene showed that only VBNC forms of E. coli O157:H7 showed viability at 62 °C for 5 min which indicated the increased resistant of VBNC bacteria to the thermal inactivation. The ability of E. coli O157:H7 to enter into VBNC state in salted fish and also the increase of its thermal resistance suggest that VBNC E. coli O157: H7 can be considered as critical threat to public health and food safety.

https://cjes.guilan.ac.ir/article_5136_34350fb37be0093b2609c2b09c64f231.pdf