Abstract: Objective: The purpose of this study was to explore whether the sigB gene palyed a regulatory role in Listeria monocytogenes (Lm) exposed to sodium hypochlorite stress. Methods: We studied the phenotypic changes and compared the percent increases in reactive oxygen species (ROS) levels in the wild-type Lm WaX12 and its sigB deletion mutant under sodium hypochlorite stress at the median lethal concentration (3 mmol/L). The changes in the transcriptional levels of lmo1433, lmo0906, lmo2344, ohrR and lmo2770 genes were investigated during sodium hypochlorite stress. Results: The wild-type strain presented a stronger tolerance to sodium hypochlorite stress than the mutant, especailly during the stationary growth phase. The percent increase in ROS levels in the wild-type strain was 19.97% higher than that in the mutant after 30 min of sodium hypochlorite stress, confirming the regulatory role of the sigB gene in Lm under sodium hypochlorite stress. Moreover, the relative expression levels of lmo1433, lmo2344 and ohrR genes in the wild-type strain were much higher than those in the mutant (P < 0.01), as revealed by RT-PCR. No significant differences in the expression levels of lmo0906 and lmo2770 were found between the wild-type and mutant strains. Conclusion: The sigB gene plays an important regulatory role in Lm exposed to NaClO stress, which may be partially achieved by directly or indirectly activating some genes regulating the redox balance in the body.

Key words: Listeria monocytogenes, sigB, sodium hypochlorite, oxidative stress, RT-PCR