Abstract: The aim of the present study was to assess the influence of storage temperature on virulence gene expression of Listeria monocytogenes (Lm) grown in a food matrix. Lm ATCC 19115 was grown in a salmon matrix or tryptone soya agar containing 0.6% yeast extract (TSA-YE) (control) at different temperatures (0, 4 and 7 ℃) for 24 and 48 h, respectively. Then, the bacterial cells were collected by centrifugation for RNA extraction using a commercial kit (TianGen, Dalian), and the expression levels of hlyA, inlB, prfA and sigB were assessed by RT-qPCR. The RT-qPCR data showed that the expression of all four major virulence genes was up-regulated when the strain was grown in a salmon matrix compared to TSA-YE at each temperature. In addition, hlyA possessed the highest expression level among these four genes. The expression levels of prfA and sigB in Lm from salmon stored at 4 ℃ were significantly higher than those at 0 and 7 ℃ (P < 0.01). The expression levels of inlB and hlyA in salmon stored for 24 h at different temperatures were in the descending order of 7 ℃ > 4 ℃ > 0 ℃ (P < 0.01). In the salmon matrix, the expression levels of all four major virulence genes at 48 h were significantly higher than those at 24 h (P < 0.01). The results of this study can provide basic information for risk assessment and control of Lm in food matrices.

Key words: Listeria monocytogenes, virulence genes, salmon matrix