EvfG is a multi-function protein located in the Type VI secretion system for ExPEC

The Type VI secretion system (T6SS) functions as a protein transport nanoweapon in several stages of bacterial life. Even though bacterial competition is the primary function of T6SS, different bacteria exhibit significant variations. Particularly in Extraintestinal pathogenic Escherichia coli (ExPEC), research into T6SS remains relatively limited. This study identified the uncharacterized gene evfG within the T6SS cluster of ExPEC RS218. Through our experiments, we showed that evfG is involved in T6SS expression in ExPEC RS218. We also found evfG can modulate T6SS activity by competitively binding to c-di-GMP, leading to a reduction in the inhibitory effect. Furthermore, we found that evfG can recruit sodA to alleviate oxidative stress. The research shown evfG controls an array of traits, both directly and indirectly, through transcriptome and additional tests. These traits include cell adhesion, invasion, motility, drug resistance, and pathogenicity of microorganisms. Overall, we contend that evfG serves as a multi-functional regulator for the T6SS and several crucial activities. This forms the basis for the advancement of T6SS function research, as well as new opportunities for vaccine and medication development.

NhaA facilitates the maintenance of bacterial envelope integrity and the evasion of complement attack contributing to extraintestinal pathogenic Escherichia coli virulence

Extraintestinal pathogenic Escherichia coli (ExPEC) is responsible for severe bloodstream infections in humans and animals. However, the mechanisms underlying ExPEC's serum resistance remain incompletely understood. Through the transposon-directed insertion-site sequencing approach, our previous study identified nhaA, the gene encoding a Na+/H+ antiporter, as a crucial factor for infection in vivo. In this study, we investigated the role of NhaA in ExPEC virulence utilizing both in vitro models and systemic infection models involving avian and mammalian animals. Genetic mutagenesis analysis revealed that nhaA deletion resulted in filamentous bacterial morphology and rendered the bacteria more susceptible to sodium dodecyl sulfate, suggesting the role of nhaA in maintaining cell envelope integrity. The nhaA mutant also displayed heightened sensitivity to complement-mediated killing compared to the wild-type strain, attributed to augmented deposition of complement components (C3b and C9). Remarkably, NhaA played a more crucial role in virulence compared to several well-known factors, including Iss, Prc, NlpI, and OmpA. Our findings revealed that NhaA significantly enhanced virulence across diverse human ExPEC prototype strains within B2 phylogroups, suggesting widespread involvement in virulence. Given its pivotal role, NhaA could serve as a potential drug target for tackling ExPEC infections.

Effects of TolC on the pathogenicity of porcine extraintestinal pathogenic Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC) is a well-known critical pathogenic zoonosis that causes extraintestinal infections in humans and animals by affecting their immune organs. Recently, research on the outer membrane protein of E. coli, tolerant colicin (TolC), a virulent protein in the formation of the ExPEC efflux pump, has been an attractive subject. However, the pathogenic mechanisms remain unclear. This study aimed to explore the role of TolC in the pathogenesis of the ExPEC strain PPECC42; a complementation strain (Cm-TolC) and an isogenic mutant (ΔTolC) were constructed. Loss of TolC drastically impaired the virulence of ExPEC in an experimental mouse model. ΔTolC showed a substantial decrease in the porcine aortic vascular endothelial cell (PAVEC) adherence, invasion, and pro-inflammatory response, in contrast to that of the wild type, with a reduced survival ratio in both the bacterial load and whole blood in mice. ΔTolC also showed decreased expression of necroptosis signals such as receptor-interacting protein kinase 1, phosphorylated mixed-lineage kinase domain-like protein, and mitochondrial proteins such as phosphoglycerate mutase family member 5. Our data suggest that TolC is closely associated with ExPEC pathogenesis. These results provide scientific grounds for exploring the potential of TolC as an effective drug target for controlling ExPEC infection, screening new inhibitors, and developing new drugs. This will allow for further prevention and control of ExPEC infection.

Ucl fimbriae regulation and glycan receptor specificity contribute to gut colonisation by extra-intestinal pathogenic Escherichia coli

Extra-intestinal pathogenic Escherichia coli (ExPEC) belong to a critical priority group of antibiotic resistant pathogens. ExPEC establish gut reservoirs that seed infection of the urinary tract and bloodstream, but the mechanisms of gut colonisation remain to be properly understood. Ucl fimbriae are attachment organelles that facilitate ExPEC adherence. Here, we investigated cellular receptors for Ucl fimbriae and Ucl expression to define molecular mechanisms of Ucl-mediated ExPEC colonisation of the gut. We demonstrate differential expression of Ucl fimbriae in ExPEC sequence types associated with disseminated infection. Genome editing of strains from two common sequence types, F11 (ST127) and UTI89 (ST95), identified a single nucleotide polymorphism in the ucl promoter that changes fimbriae expression via activation by the global stress-response regulator OxyR, leading to altered gut colonisation. Structure-function analysis of the Ucl fimbriae tip-adhesin (UclD) identified high-affinity glycan receptor targets, with highest affinity for sialyllacto-N-fucopentose VI, a structure likely to be expressed on the gut epithelium. Comparison of the UclD adhesin to the homologous UcaD tip-adhesin from Proteus mirabilis revealed that although they possess a similar tertiary structure, apart from lacto-N-fucopentose VI that bound to both adhesins at low-micromolar affinity, they recognize different fucose- and glucose-containing oligosaccharides. Competitive surface plasmon resonance analysis together with co-structural investigation of UcaD in complex with monosaccharides revealed a broad-specificity glycan binding pocket shared between UcaD and UclD that could accommodate these interactions. Overall, our study describes a mechanism of adaptation that augments establishment of an ExPEC gut reservoir to seed disseminated infections, providing a pathway for the development of targeted anti-adhesion therapeutics.

ExPEC infection of the urinary tract and bloodstream is frequently seeded from an intestinal reservoir, necessitating an understanding of the mechanisms that promote gut colonisation. Here we employed molecular and structural approaches to define the regulation and function of ExPEC Ucl fimbriae as a gut colonisation factor. We describe how mutations in the non-coding regulatory region of the ucl promoter cause increased Ucl fimbriae expression and promote enhanced gut colonisation via tuned induction by a global regulator that senses oxygen stress. We further define the glycan receptor targets of Ucl fimbriae and characterise the structural features of the Ucl adhesin that facilitate these interactions. These findings explain how ExPEC can adapt to survival in the gut to seed extra-intestinal infection.

Characterization and distinction of two flagellar systems in extraintestinal pathogenic Escherichia coli PCN033

Extraintestinal pathogenic Escherichia coli (ExPEC) can invade and colonize multiple extraintestinal tissues and can cause a wide range of infections; however the mechanisms of its pathogenicity are not well understood. Flagella contribute to the infection of E. coli strains by mediating adhesion and invasion. Our previous bioinformatic analysis revealed two flagella gene clusters in the genome of an ExPEC isolate, PCN033. One encodes the conventional flagellum system (Flag-1) and the other encodes the Flag-2 system, whose function is uncharacterized. Here we aimed to characterize these two flagellum systems and determine their contributions to the flagellum formation and certain pathogenicity-associated phenotypes. Our observations support the involvement of Flag-1 system, but not Flag-2 system, in the synthesis and maturation of the flagellum structure, and in mediating bacterial swimming and swarming. Moreover, flgD, which encodes a flagellar-hook scaffolding protein in the Flag-1 system, is required for flagellum assembly by influencing the production of FliC (flagellin). Deletion of flgD attenuated ExPEC strain PCN033 invasion and colonization in vivo, probably by affecting bacterial adhesion and invasion, and by reducing resistance to phagocytosis by circulating monocytes. In contrast, these phenotypes were not observed in the strain with deletion of lfgD, encoding the FlgD-like protein in the Flag-2 system. Taken together, these findings indicate that Flag-1 flagellum system is the determinative component of bacterial flagella that contributes to the infection.

[Dual deletion of the kpsE and kpsD genes reduced the bacterial virulence of extraintestinal pathogenic Escherichia coli]

OBJECTIVE

To study the role of capsule polysaccharide in pathogenesis of extraintesinal pathogenic Escherichia coli (ExPEC).

METHODS

By using λ Red recombination system, we generated the capsular polysaccharide transport associated genes kpsE and kpsD double knockout mutants E058ΔkpsED and U17ΔkpsED. We then compared and analyzed the characteristics of the mutant strains and wild-type strains.

RESULTS

The growth curves in Luria Bertani showed that the deletion of kpsED did not affect growth kinetics of the mutants. The abilities of resistance to serum and killing by chicken macrophages were significantly impaired. LD50 results showed that the double mutants completely abolished the virulence, whereas the complementation strains restored the virulence to resemble that of wild-type strains, and the colonization and coinfection model demonstrated that the deletion of kpsED led to attenuation of virulence, because the double mutant showed significantly decreased colonization compared with the wild-type strains in all organs tested in chickens.

CONCLUSION

These results indicated that the virulence factors encoded by capsule genes were important for the pathogenesis of ExPEC.

Differential Regulation of the Surface-Exposed and Secreted SslE Lipoprotein in Extraintestinal Pathogenic Escherichia coli

Extra-intestinal pathogenic Escherichia coli (ExPEC) are responsible for diverse infections including meningitis, sepsis and urinary tract infections. The alarming rise in anti-microbial resistance amongst ExPEC complicates treatment and has highlighted the need for alternative preventive measures. SslE is a lipoprotein secreted by a dedicated type II secretion system in E. coli that was first identified as a potential vaccine candidate using reverse genetics. Although the function and protective efficacy of SslE has been studied, the molecular mechanisms that regulate SslE expression remain to be fully elucidated. Here, we show that while the expression of SslE can be detected in E. coli culture supernatants, different strains express and secrete different amounts of SslE when grown under the same conditions. While the histone-like transcriptional regulator H-NS strongly represses sslE at ambient temperatures, the variation in SslE expression at human physiological temperature suggested a more complex mode of regulation. Using a genetic screen to identify novel regulators of sslE in the high SslE-expressing strain UTI89, we defined a new role for the nucleoid-associated regulator Fis and the ribosome-binding GTPase TypA as positive regulators of sslE transcription. We also showed that Fis-mediated enhancement of sslE transcription is dependent on a putative Fis-binding sequence located upstream of the -35 sequence in the core promoter element, and provide evidence to suggest that Fis may work in complex with H-NS to control SslE expression. Overall, this study has defined a new mechanism for sslE regulation and increases our understanding of this broadly conserved E. coli vaccine antigen.