The change in heat inactivation of Escherichia coli O157:H7 after entering into the viable but non-culturable state in salted fish, Hypophthalmichthys molitrix
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 molitri...
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Veröffentlicht in: | Caspian journal of environmental sciences 2021-10, Vol.19 (4), p.629-637 |
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Zusammenfassung: | 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. |
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ISSN: | 1735-3033 1735-3866 |
DOI: | 10.22124/cjes.2021.5136 |