Loss of Regulatory Protein RfaH Attenuates Virulence of Uropathogenic Escherichia coli

Abstract

RfaH is a regulatory protein in Escherichia coli and Salmonella enterica serovar Typhimurium. Although it enhances expression of different factors that are proposed to play a role in bacterial virulence, a direct effect of RfaH on virulence has not been investigated so far. We report that inactivation of rfaH dramatically decreases the virulence of uropathogenic E. coli strain 536 in an ascending mouse model of urinary tract infection. The mortality rate caused by the wild-type strain in this assay is 100%, whereas that of its isogenic rfaH mutant does not exceed 18%. In the case of coinfection, the wild-type strain 536 shows higher potential to colonize the urinary tract even when it is outnumbered 100-fold by its rfaH mutant in the inoculum. In contrast to the wild-type strain, serum resistance of strain 536rfaH::cat is fully abolished. Furthermore, we give evidence that, besides a major decrease in the amount of hemin receptor ChuA (G. Nagy, U. Dobrindt, M. Pathogenic strains of Escherichia coli produce virulence factors that differentiate them from commensal variants of the same species and enable them to cause disease. Constitutive expression of virulence determinants, however, would be needless and energetically exhausting for bacteria. Moreover, the presence of some virulence factors could even be disadvantageous at certain points of the infectious process. For effective pathogenesis, bacteria sense their environment and regulate the expression of genes encoding virulence factors. This response to environmental signals is usually mediated by specific or global regulators, which often form a correlative, complex network (for a review, see reference 15). A regulatory protein has been described in gram-negative bacteria which was first demonstrated to have an influence on lipopolysaccharide (LPS) core synthesis and therefore was named RfaH (23).The RfaH protein acts as a transcriptional regulator in E. coli, Salmonella enterica serovar Typhimurium, and possibly in other gram-negative bacteria (3). During the last two decades, several operons that are dependent on RfaH for full expression were identified in various strains. These include rfa, rfb, hly, tra, chu, cps, and kps, whose altered expressions in the absence of RfaH result in a decreased amount of LPS core (23), Oantigen (42), alpha-hemolysin (5, 22), F-factor (35), hemin receptor (29), and group I (32), group II (39), and group III (9) capsules, respectively. The exact mechanism by which RfaH enhances expression of these components is not yet fully understood. According to the present view, RfaH regulation takes place at the level of transcriptional antitermination, hence suppressing operon polarity (3). The effect of RfaH is highly dependent on a cis-acting region termed JUMPStart sequence. Recently, the association of RfaH with an 8-bp motif located within the JUMPStart sequence (the ops element) was described (4).Interestingly, all determinants affected by RfaH encode components that are exported from the bacterial cell or anchored in the outer me...

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“…The infant mouse model of ascending UTI was used as described in ref. 65. In the murine sepsis model, female 8-week-old Naval Medical Research Institute (NMRI) mice were intravenously infected in two independent experiments.…”

Regulation of type 1 fimbriae synthesis and biofilm formation by the transcriptional regulator LrhA of Escherichia coli

“…After incubation for some minutes on ice, agglutination occurred. Expression of S or P fimbriae was also checked by Western blot analysis using polyclonal sera raised against S or P fimbriae of E. coli strain 536, as described by Nagy et al (2002).…”

Expression of the Yersinia enterocolitica O:3 LPS O-antigen and outer core gene clusters is RfaH-dependent

“…In E. coli, deletion of rfaH results in downregulation of virulence factors such as LPS, K15 capsule, a-haemolysin and haemin receptor ChuA (Nagy et al, 2002). Likewise, a Salmonella rfaH mutant having an aberrant cell wall structure grew poorly in epithelial cells and macrophages.…”