Role of Gene Regulated by CpxR in the Survival of Serovar Enteritidis in Antibacterial Egg White.

The survival ability of serovar Enteritidis in antibacterial egg white is an important factor leading to outbreaks through eggs and egg products. In this study, the role of the gene , encoding an inner membrane protein, in the survival of Enteritidis in egg white, and its transcriptional regulation by CpxR were investigated. Quantitative reverse transcription-PCR (RT-qPCR) results showed that the gene expression was upregulated 35-fold after exposure to egg white for 4 h compared to that in M9FeS medium, and the deletion of () dramatically decreased the survival rate of bacteria in egg white to less than 1% of the wild type (WT) and the complementary strain at both 37 and 20°C, indicating that was essential for bacteria to survive in egg white. Furthermore, the strain was sensitive to a 3-kDa ultrafiltration matrix of egg white because of its high pH and antimicrobial peptide components. Putative conserved binding sites for the envelope stress response regulator CpxR were found in the promoter region. , the RT-qPCR assay results showed that the upregulation of in a strain in egg white was 1/5 that of the WT. , results from DNase I footprinting and electrophoretic mobility shift assays further demonstrated that CpxR could directly bind to the promoter region, and a specific CpxR binding sequence was identified. In conclusion, it was shown for the first time that CpxR positively regulated the transcription of , which was indispensable for survival of Enteritidis in egg white. serovar Enteritidis is the predominant serotype that causes human salmonellosis mainly through contaminated chicken eggs or egg products and has been a global public health threat. The spread and frequent outbreaks of this serotype through eggs correlate significantly with its exceptional survival in eggs, despite the antibacterial properties of egg white. Research on the survival mechanisms of Enteritidis in egg white will help develop effective strategies to control the contamination of eggs by this serotype and help further elucidate the complex antibacterial mechanisms of egg white. This study revealed the importance of , a gene with unknown function, on the survival of Enteritidis in egg white, as well as its transcriptional regulation by CpxR. Our work provides the basis to reveal the mechanisms of survival of Enteritidis in egg white and the specific function of the gene.