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

Abstract

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...

Genome Sequences and Phylogenetic Analysis of K88- and F18-Positive Porcine Enterotoxigenic Escherichia coli

“…This region was similar to the urease-tellurite islands found in E. coli O157:H7 strains, EHEC O26:H11 strain 11368, and EHEC O111:H Ϫ strain 11128 (51). Previous studies have identified this island among porcine ETEC O149:K88 strains (39), and portions of this island in E. coli O157:H7 were shown to be involved in colonization to ligated pig intestine (56). Therefore, this island might be important for the colonization of UMNK88 and other K88 strains.…”

Distribution of Pathogenicity Islands OI-122, OI-43/48, and OI-57 and a High-Pathogenicity Island in Shiga Toxin-Producing Escherichia coli

“…Urease has been confirmed as an important virulence factor in several bacterial species, such as Helicobacter pylori, Yersinia enterocolitica, Proteus mirabilis, Brucella species, and Klebsiella pneumoniae (31). Mutation of ureC has led to a reduced adherence of EHEC O157:H7 in ligated pig intestine (12). A recent study by Steyert and Kaper (32) revealed that strains with nonfunctional urease were 2-fold less likely to survive passage through the stomach and had a reduced ability to colonize the mouse intestinal tract compared to urease-positive strains.…”

“…The role of tellurite resistance genes (terZABCDEF) in STEC is still not well understood. Yin et al (12) showed that mutation of the ter cluster in O157:H7 led to fewer adherence to epithelial cells and smaller bacterial clusters compared to wildtype strains. Therefore, ter genes might encode an adhesin or a gene product that promotes the function of adhesion(s).…”

“…OI-43/48 genes are divided into three functional groups: a seven-gene cluster ureDABCEFG that encodes urease and accessory proteins hydrolyzing urea to ammonia and carbon dioxide; telluride resistance genes terZABCDEF (11); and two putative adhesion genes, iha (iron-regulated gene A) and aidA-1 (autotransporter adhesin involved in diffuse adherence) (12).…”

The role of TerW protein in the tellurite resistance of uropathogenic Escherichia coli

“…The introduction of the ter operon from uropathogenic E. coli KL53 into non-pathogenic and uropathogenic E. coli (ter-gene free) showed that the presence of the ter loci improved the fitness of bacterial strains by enabling them to survive inside macrophages (Valkova et al 2007). Deletion of the Te R region reduced the ability of the strain to adhere to epithelial cells in vitro and in ligated pig ileal loops (Yin et al 2009). In spite of the rare occurrence of tellurite in nature, the acquisition of the ter operon could offer some selective advantage to pathogens in natural environments, such as the urinary tract of humans, and facilitate colonisation despite immune assault.…”