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Strain and host-cell dependent role of type-1 fimbriae in the adherence phenotype of super-shed Escherichia coli O157:H7.

ABSTRACT: Super-shed (SS) Escherichia coli O157 (E. coli O157) demonstrate a strong, aggregative, locus of enterocyte effacement (LEE)-independent adherence phenotype on bovine recto-anal junction squamous epithelial (RSE) cells, and harbor polymorphisms in non-LEE-adherence-related loci, including in the type 1 fimbriae operon. To elucidate the role of type 1 fimbriae in strain- and host-specific adherence, we evaluated the entire Fim operon (FimB-H) and its adhesion (FimH) deletion mutants in four E. coli O157 strains, SS17, SS52, SS77 and EDL933, and evaluated the adherence phenotype in bovine RSE and human HEp-2 adherence assays. Consistent with the prevailing dogma that fimH expression is genetically switched off in E. coli O157, the ΔfimHSS52, ΔfimB-HSS52, ΔfimB-HSS17, and ΔfimHSS77 mutants remained unchanged in adherence phenotype to RSE cells. In contrast, the ΔfimHSS17 and ΔfimB-HSS77 mutants changed from a wild-type strong and aggregative, to a moderate and diffuse adherence phenotype, while both ΔfimHEDL933 and ΔfimB-HEDL933 mutants demonstrated enhanced binding to RSE cells (p < 0.05). Additionally, both ΔfimHSS17 and ΔfimHEDL933 were non-adherent to HEp-2 cells (p < 0.05). Complementation of the mutant strains with their respective wild-type genes restored parental phenotypes. Microscopy revealed that the SS17 and EDL933 strains indeed carry type 1 fimbriae-like structures shorter than those seen in uropathogenic E. coli. Taken together, these results provide compelling evidence for a strain and host cell type-dependent role of fimH and the fim operon in E. coli O157 adherence that needs to be further evaluated.

SUBMITTER: Katani R

PROVIDER: S-EPMC8605689 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Adherence of pathogenic Escherichia coli strains to intestinal epithelia is essential for infection. For enterohemorrhagic E. coli (EHEC) serotype O157:H7, we have previously demonstrated that multiple factors govern this pathogen's adherence to HeLa cells (A. G. Torres and J. B. Kaper, Infect. Immun. 71:4985-4995, 2003). One of these factors is CadA, a lysine decarboxylase, and this protein has been proposed to negatively regulate virulence in several enteric pathogens. In the case of EHEC strains, CadA modulates expression of the intimin, an outer membrane adhesin involved in pathogenesis. Here, we inactivated cadA in O157:H7 strain 86-24 to investigate the role of this gene in EHEC adhesion to tissue-cultured monolayers, global gene expression patterns, and colonization of the infant rabbit intestine. The cadA mutant did not possess lysine decarboxylation activity and was hyperadherent to tissue-cultured cells. Adherence of the cadA mutant was nearly twofold greater than that of the wild type, and the adherence phenotype was independent of pH, lysine, or cadaverine in the media. Additionally, complementation of the cadA defect reduced adherence back to wild-type levels, and it was found that the mutation affected the expression of the intimin protein. Disruption of the eae gene (intimin-encoding gene) in the cadA mutant significantly reduced its adherence to tissue-cultured cells. However, adherence of the cadA eae double mutant was greater than that of an 86-24 eae mutant, suggesting that the enhanced adherence of the cadA mutant is not entirely attributable to enhanced expression of intimin in this background. Gene array analysis revealed that the cadA mutation significantly altered EHEC gene expression patterns; expression of 1,332 genes was downregulated and that of 132 genes was upregulated in the mutant compared to the wild-type strain. Interestingly, the gene expression variation shows an EHEC-biased gene alteration including intergenic regions. Two putative adhesins, flagella and F9 fimbria, were upregulated in the cadA mutant, suggestive of their association with adherence in the absence of the Cad regulatory mechanism. In the infant rabbit model, the cadA mutant outcompeted the wild-type strain in the ileum but not in the cecum or mid-colon, raising the possibility that CadA negatively regulates EHEC pathogenicity in a tissue-specific fashion.

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Strain and host-cell dependent role of type-1 fimbriae in the adherence phenotype of super-shed Escherichia coli O157:H7.

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