Molecular Epidemiological and Phylogenetic Associations of Two Novel Putative Virulence Genes, iha and iroN _{E. coli} , among Escherichia coli Isolates from Patients with Urosepsis

Abstract

Two novel putative Escherichia coli virulence genes, iha and iroN from E. coli (iroN E. coli ), were detected in 55 and 39%, respectively, of 67 E. coli isolates from patients with urosepsis. iha and iroN E. coli exhibited divergent associations with other putative virulence genes, phylogenetic markers, host characteristics, and antimicrobial resistance.The virulent strains of Escherichia coli that cause urinary tract infections (UTIs) and other extraintestinal infections in humans (i.e., extraintestinal pathogenic E. coli [ExPEC]) owe their pathogenic potential largely to the presence of specialized virulence factors (VFs) which are absent from commensal members of the species and which allow ExPEC strains to colonize host mucosal surfaces, injure and invade host tissues, foil host defense mechanisms, and incite an injurious host inflammatory response (4,5,9,20). Currently recognized putative VFs (PVFs) of ExPEC include adhesins, siderophores, toxins, protectins, and invasins, some of which are encoded on pathogenicity-associated islands (PAIs) (2,7,8,17,24,26). PAIs are large blocks of established or suspected virulence genes that are inserted into the E. coli genome (often at tRNA loci) and which may provide a mechanisms for coordinate horizontal transfer of virulence genes between lineages within E. coli and even between species (3,7,21,24,25).Two recently described PAI-linked PVF genes of ExPEC, iha and iroN from E. coli (iroN E. coli ), are of interest both in their own right and because of their potential utility as markers for their respective PAIs of origin (23,27). iha, an novel nonhemagglutinating adhesin which in vitro confers HeLa cell adherence capability to (nonadhering) E. coli K-12, was first identified as part of a tellurite resistance-associated PAI (termed TAI, the tellurite resistance-adherence-conferring island) from an E. coli O157:H7 isolate from a patient with hemorrhagic colitis (27). iha exhibits nearly perfect sequence identity with the sequenced portion of an open reading frame (ORF) of unknown function (ORF "R4") from a PAI in archetypal ExPEC strain CFT073 (8,17). In addition to the iha homologue and multiple other ORFs of unknown significance, this PAI from strain CFT073 also contains an hly (hemolysin) operon and one of the strain's two pap operons (named for pilus associated with pyelonephritis; P fimbriae), which includes the F7-2 allele of papA (the P fimbrial structural subunit gene) and allele II of papG (the P fimbrial digalactoside-specific adhesin gene) (8,16,17). Consistent with the hypothesis that iha is a PVF in ExPEC, probes derived from PAI regions immediately adjacent to iha as it occurs in strain CFT073 hybridized significantly more frequent with UTI or bacteremia isolates of E. coli than with commensal E. coli (8).iroN E. coli , a novel catechole siderophore receptor which exhibits increased expression in urine, was recently identified in archetypal ExPEC strain CP9 as part of a PAI which also includes one of this strain's two pap operons (i.e., the pap operon con...

Expression of the Escherichia coli IrgA homolog adhesin is regulated by the ferric uptake regulation protein

“…Johnson et al found that iha was present in 55% of urosepsis isolates and was more prevalent in isolates from immunocompetent hosts, suggesting that Iha confers some pathogenic advantage [12]. In a different study, Johnson et al found that presence of iha predicted multiple same-strain recurrences of urinary tract infections (UTI) [13].…”

Virulence factors and antimicrobial resistance of escherichia coli isolated from urinary tract of swine in southern of Brazil

“…The primers and PCR conditions were previously described (1,2,4,7,12,15,16). Amplicons identities were confirmed by sequencing (Amersham Pharmacia Biotech).…”

Differential effects of short-chain fatty acids and iron on expression of iha in Shiga-toxigenic Escherichia coli

“…Iha is a potentially important accessory virulence factor for several pathotypes of E. coli, including STEC, UPEC and avian-pathogenic strains (Ewers et al, 2007;Johnson et al, 2000;Ons et al, 2007;Rodriguez-Siek et al, 2005;Touati, 2000), functioning as an adhesin and, at least for UPEC, as a catecholate siderophore receptor (Leveille et al, 2006). This latter function is consistent with the fact that iha is induced under iron-limiting conditions and is subject to Fur-mediated repression in iron-replete environments in both UPEC and O157:H7 STEC strains (Leveille et al, 2006;Rashid et al, 2006b), as well as in the hyper-virulent LEE-negative STEC strain 98NK2, as shown in this study.…”

“…Among STEC a range of novel adhesins have been identified, including the chromosomally encoded adherence-conferring protein Iha, a homologue of Vibrio cholera IrgA . Iha was first characterized in E. coli O157:H7, but it is distributed widely among LEEnegative and LEE-positive STEC, as well as in uropathogenic E. coli (UPEC) (Johnson et al, 2000;Tarr et al, 2000). Tarr et al (2000) reported that an iha deletion mutant of O157:H7 STEC was impaired in adherence to HeLa cells, although the difference did not reach statistical significance.…”