奇異變形桿菌qseEGF之探討

Abstract

Proteus mirabilis is a facultative anaerobic, Gram-negative bacterium and a member of the Enterobacteriaceae family. It belongs to normal flora of human intestine. It usually causes, however, urinary tract infection (UTI), and leads to kidney disease, pneumonia and septicemia in individuals with long-term catheterization or with structural or functional abnormalities in the urinary tract. QseEGF, first described in enterohaemorrhagic Escherichia coli, is one of two-component systems in bacteria. QseEGF can sense signals like bacterial AI-2 and epinephrine from host cells. Activation of QseEGF regulates virulence genes, like LEE genes, causing attaching and effacing lesions (A/E lesions), or Shiga toxin, causing hemolytic-uremic syndrome (HUS). To understand the role of QseEGF in P. mirabilis, in this study we constructed qseEGF mutant. We found mutation in qseEGF caused pleiotropic phenotypic effects in P. mirabilis. The swarming ability of qseEGF mutant was lower than wild-type (Wt). In this regard, production of swarmer cells of the qseEGF mutant was delayed and swarm cell length was much shorter than Wt. The swarming ability was restored to near the wt level in the QseEGF-complemented strain. Besides, we demonstrated the qseEGF mutant displayed decreased haemolysin ability and cytotoxicity. We next explore why QseEGF regulates swarming motility. We found mutation in qseEGF decreased flhDC and flagella expression in swarming condition. In addition, we tested possible signals of QseEGF. We found urea inhibited the swarming motility of Wt but not in qseEGF mutant. Reporter assay also showed flhDC expression of Wt but not qseEGF mutant was decreased in the presence of urea. We thought that urea was one negative signal for the QseEGF signaling pathway. To further understand the role of qseEGF gene in swarming, we tested rcsB, which negatively regulates flhDC expression, expression in Wt and qseEGF mutant. We found expression rcsB in qseEGF mutant was higher than Wt. Knowing MR/P frimbriae are required for adhering to urinary tract epithelial cells of mouse, we examined the role of QseEGF in the expression of MR/P fimbriae and found that qseEGF mutant didn’t produce MrpA protein, the subunit of MR/P frimbriae, by western blot. In summary, we found that QseEGF plays an important role in swarming of P. mirabilis by sensing the surface contact stimulus or urea to positively or negatively regulate flhDC expression. Besides, QseEGF also regulates expression of virulence factors such as MR/P fimbriae and hence might contribute to UTI of P. mirabilis.