Pathoadaptive Mutation That Mediates Adherence of Shiga Toxin-Producing Escherichia coli O111

Abstract

The adherence of pathogenic Escherichia coli strains to intestinal epithelium is essential for initiation of infection. The cad operon encodes the lysine decarboxylase (LDC) system responsible for metabolizing lysine, and this operon has been proposed as an antivirulence mechanism in enteroinvasive E. coli and Shigella flexneri and as a factor mediating E. coli O157:H7 adherence. We sought to determine whether the LDC activity was present in a phylogenetically characterized collection of diarrheagenic E. coli (DEC) strains and to establish whether its expression was associated with their adherence to tissue culture cells. LDC activity was found in most of the pathogenic E. coli strains tested and was absent from Shiga toxin-producing E. coli (STEC) O111 strains (DEC pathotype 8). Analysis of the cad region in these O111 strains indicates that the operon has been rearranged and some of the genes are either missing or disrupted. A similar rearrangement was found in an E. coli O111:H8 strain recently isolated from an outbreak in Texas. Complementation of the LDC-negative strains with the cad operon in trans restored the LDC activity and resulted in a reduction in adherence to tissue culture cells. Initial analysis of the protein profiles on the surface of the O111 strains indicates that the LDC activity has an effect on the expression of the adhesin intimin. Cadaverine had a slight effect on LDC-negative strain adhesion but none on intimin expression. Our data suggest that this pathoadaptive mutation is an important mechanism to control functions potentially implicated in the pathogenesis of these organisms.

CadA Negatively Regulates Escherichia coli O157:H7 Adherence and Intestinal Colonization

“…Strains were routinely grown in Luria-Bertani (LB) broth or on L agar at 37°C (17). The construction of plasmid pCadABC, a pBR322 derivative containing the cad locus, has been described previously (36). Plasmids pVS50Z and pVS24Z, pRS551 derivatives containing the eae and tir promoter regions, respectively, were obtained from V. Sperandio (29).…”

“…From the 80 DEC strains analyzed, 4 were LDC-negative strains corresponding to serotypes O111:NM, O111:H8, and O26:NM. Analysis of the cad locus indicated that this region was rearranged, and some of the genes were either missing or disrupted when compared to the E. coli K-12 cad region (36). Interestingly, the introduction of the cad locus on a plasmid to the strains lacking the LDC region reduced their adhesion compared to that of their corresponding wild-type LDC-negative strains.…”

“…A correlation between the inability to decarboxylate lysine and the isolation of clinically relevant EHEC and other Shiga toxin-producing E. coli (STEC) strains has been reported previously, although no direct link to adherence was identified (9,10,39,41). A study by our group investigated the relationship between LDC activity and adherence to tissuecultured cells in a phylogenetically characterized collection of diarrheagenic E. coli (DEC) strains (36). From the 80 DEC strains analyzed, 4 were LDC-negative strains corresponding to serotypes O111:NM, O111:H8, and O26:NM.…”

“…Interestingly, the introduction of the cad locus on a plasmid to the strains lacking the LDC region reduced their adhesion compared to that of their corresponding wild-type LDC-negative strains. Finally, complementation studies showed that the products encoded in the cad operon affected the expression of intimin, a common adhesin expressed in STEC and enteropathogenic E. coli (EPEC) strains (36). A larger screen to determine whether the lack of LDC activity was a widespread phenotype in different serogroups of E. coli was recently performed by Jores et al (11).…”

Intestinal barrier: A gentlemen’s agreement between microbiota and immunity

“…In the intestine, an infectious process usually starts with adhesion to the brush border of intestinal cells [31,32] . After the adhesion phase, pathogenic bacteria produce virulence factors that are secreted in the external environment or injected into the cytosol of host cells.…”