Investigating the Possibility of the Listeria Monocytogenes Entering Into a Viable But Non-Culturable (VBNC) Form and Expression of the Pathogenic Genes During the Frozen Storage of (-18ºC) Rainbow Trout Fish Nugget

Background and Aims: The purpose of this study was to investigate the possibility of Listeria monocytogenes entering the VBNC state during the frozen storage and the expression of its pathogenic genes Materials and Methods: Bacteria in 106 Colony counts of in mid log phase were inoculated into three Culture medium including Normal Saline (NS), BHI Broth and Fish Broth (FB) and kept at -18ºCfor 2 months and examined. Then, bacteria were evaluated on enriched medium BHI agar using culture methods (colony count) over times 4 and 8 hours, 2, 4, 8, 20, 30 and 60 days after the freezing shock using the method of RT-PCR for investigating the expression of 16S rRNA, hly and inlA genes; they were evaluated before and after the freezing shock. Results: This bacterium retained its ability to cultivate until the end of the shock, but reduced its number. Freezing stopped the expression of genes of hly and inlA, as these genes were not expressed in a rich culture medium either. By adding blood to the rich culture medium of this bacterium, only the hemolysin O pathogen gene was expressed. Conclusion: Although freezing does not lead to the introduction of this bacterium into the VBNC state, it is effective as an adverse environmental factor for the bacteria in the expression of its pathogenic genes. Blood and its agents can act as an agent for the induction and clarification of the hly gene, and the expression of pathogenic bacterial genes are independent of each other.