Molecular and Population Genetics of Virulence Traits in<i>Escherichia Coli</i>O157:H7

Benson, Andrew K.

doi:10.1002/9780470752616.ch17

Cited by 1 publication

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“…The urease genes are similar to the genes in Klebsiella aerogenes (9) while the Te r gene cluster is similar to the genes in Serratia marcesens (28). The pattern of homology indicates that the TAI is a mosaic of functional regions that were acquired on separate occasions (1). Iha is an IrgA (iron-regulated gene A) homolog adhesin (25).…”

Section: O Island 48 (Oi-mentioning

confidence: 89%

Contributions of O Island 48 to Adherence of Enterohemorrhagic Escherichia coli O157:H7 to Epithelial Cells In Vitro and in Ligated Pig Ileal Loops

Wheatcroft

Chambers

et al. 2009

Appl Environ Microbiol

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O island 48 (OI-48) ofThe OI-48 aidA gene deletion had no effect on adherence in vitro or in vivo. Deletion of the iha and ureC genes had no effect on adherence in vitro but significantly reduced the colonization of EHEC O157:H7 in the ligated pig intestine. These data suggest that Te r , Iha, and urease may contribute to EHEC O157:H7 pathogenesis by promoting adherence of the pathogen to the host intestinal epithelium.The genome of enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain EDL933 contains unique blocks of sequences called O islands (OIs), which are absent from the E. coli K12 MG1655 genome. The OIs contain 1,387 genes, some of which encode virulence factors (21), thus making these OIs pathogenicity islands (PAIs). EHEC pathogenicity is mainly determined by factors encoded in these PAIs, such as OI-148 (locus of enterocyte effacement [LEE] PAI) which causes attaching and effacing (AE) lesions, and OI-45 and OI-93, which contain lambdoid phages encoding verotoxins that are required for bloody diarrhea and the hemolytic uremic syndrome. However, only 40% of the OI genes in O157:H7 strain EDL933 have been assigned a function.OI-43 and OI-48 are duplicates, encoding tellurite resistance (Te r ) and the putative adhesin Iha and are therefore called Te r -and adherence-conferring islands (TAIs) (28). EHEC O157:H7 strain EDL933 contains both OI-43 and OI-48, while the Sakai strain contains only one of these OIs. We used PCR with OI junction primers to show that O157:H7 strain 86-24 contains only OI-48, not OI-43 (data not shown). The TAI can be divided into three functional gene clusters, one encoding urease, a second encoding Te r , and the third encoding the putative adhesins Iha and AIDA-1 (Fig. 1) (21, 28). The urease genes are similar to the genes in Klebsiella aerogenes (9) while the Te r gene cluster is similar to the genes in Serratia marcesens (28). The pattern of homology indicates that the TAI is a mosaic of functional regions that were acquired on separate occasions (1). Iha is an IrgA (iron-regulated gene A) homolog adhesin (25). Because of its presence in eae (E. coli AE)-negative verotoxigenic E. coli (VTEC) strains, it has been suggested that Iha may function as an adhesin in these organisms in place of intimin (23,25). AIDA-I, encoded by aidA, is an autotransporter membrane protein with a ␤-barrel structure, and it confers on enteropathogenic E. coli the ability to diffusely adhere to epithelial cells. The AIDA-I adhesin from OI-48 has 68% homology to the AIDA-I of enteropathogenic E. coli (20,21). However, the roles of Iha and AIDA-I-like adhesins in EHEC pathogenesis have yet to be determined.The ure gene cluster consists of three structural genes, ureA, ureB, and ureC, and four accessory genes, ureD, ureE, ureF, and ureG, required for transport and processing of urease (5, 15). Interestingly, ure genes are more frequently present in eaepositive VTEC strains (113 of 132, or 85.6%) than in eaenegative VTEC strains (4 of 70, or 5.7%) although there is no physical linkage of the ure gen...

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