The RNA chaperone Hfq regulates expression of fimbrial-related genes and virulence of Salmonella enterica serovar Enteritidis

Salmonella Enteritidis is an intracellular pathogen that causes enteritis and systemic disease in humans and other animals. The RNA chaperone protein Hfq mediates the binding of small noncoding RNAs to target mRNA and assists in post-transcriptional gene regulation in bacteria. In this study, we constructed an hfq deletion mutant in S.Enteritidis SE50336 and analyzed the expression of major fimbrial subunits sefA, bcfA, fimA, safA, stbA, sthA, csgA, csgD, and pegA using quantitative real-time PCR. The gene expression of sefA increased about 14-fold in the hfq mutant, as compared with its expression in the wild-type strain. The expression of fimA and pegA did not change significantly, while the expression of the other fimbrial genes was significantly down-regulated in the hfq mutant. The ability of SE50336hfq adhering to Caco-2 cells was also reduced as compared with wild-type adherence. The virulence of the hfq mutant was significantly reduced in a 1-day-old chicken model of S.Enteritidis disease, as determined by quantifying the lethal dose 50% of the bacterial strains. We conclude that Hfq critically contributes to S.Enteritidis virulence, likely partially affected by regulating fimbrial gene expression.