Inactivation of ibeA and ibeT Results in Decreased Expression of Type 1 Fimbriae in Extraintestinal Pathogenic Escherichia coli Strain BEN2908

Abstract

IbeA in extraintestinal pathogenic Escherichia coli (ExPEC) strains was previously described for its role in invasion. Here we investigated the role of IbeA and IbeT, encoded by a gene located downstream of ibeA, in the adhesion of the avian ExPEC strain BEN2908 to human brain microvascular endothelial cells (HBMEC). The ⌬ibeA mutant was less adhesive to HBMEC than the wild-type strain BEN2908 was. Because strain BEN2908 also expresses type 1 fimbriae, we measured the adhesion specifically due to IbeA by comparing the adhesive properties of a ⌬fim derivative of strain BEN2908 to those of a double ⌬fim ⌬ibeA mutant. No differences were observed, indicating that the reduction of adhesion in BEN2908 ⌬ibeA could be due to a decrease in type 1 fimbria expression. We indeed showed that the decreased adhesion of BEN2908 ⌬ibeA was correlated with a decrease in type 1 fimbria expression. Accordingly, more bacteria had a fim promoter orientated in the off position in a culture of BEN2908 ⌬ibeA than in a culture of BEN2908. Expression of fimB and fimE, two genes encoding recombinases participating in controlling the orientation of the fim promoter, was decreased in BEN2908 ⌬ibeA. A reduction of type 1 fimbria expression due to a preferential orientation of the fim promoter in the off position was also seen in an ibeT mutant of strain BEN2908. We finally suggest a role for IbeA and IbeT in modulating the expression of type 1 fimbriae through an as yet unknown mechanism.Extraintestinal pathogenic Escherichia coli (ExPEC) strains are responsible for a wide range of diseases in humans and animals. In humans, almost 80% of urinary tract infections, as well as almost 20% of newborn meningitis cases, are caused by ExPEC strains (23,45). In chickens, ExPEC strains are responsible for avian colibacillosis, which results in different syndromes, ranging from superficial dermatitis to respiratory infections that frequently develop into systemic infections (12,32). Phylogenetic studies have shown that avian ExPEC strains are closely related to human ExPEC strains (40, 44). Additionally, avian ExPEC strains share common virulence genes with ExPEC strains isolated from patients with urinary tract infections or meningitis (16,40,44). Several potential virulence factors have been described for ExPEC strains. These virulence factors confer different properties, such as adhesion to host cells through type 1 and P fimbriae, iron acquisition, toxic activity toward eukaryotic cells (cytotoxins), and resistance to host defenses.ibeA is an ExPEC virulence gene that was first described for strain RS218, isolated from a patient with human newborn meningitis (26,46). ibeA encodes a 50-kDa protein and is located on the GimA genomic island. This island is inserted between yjiD and yjiE and is predicted to contain four operons, three of them potentially involved in carbohydrate metabolism (24). In addition to ibeA, the GimA4 operon is predicted to contain two other genes, ibeR and ibeT. ibeR encodes a potential transcriptional activator homologous to t...

New Role for the ibeA Gene in H2O2 Stress Resistance of Escherichia coli

“…In the APEC strain BEN2908, the deletion of ibeA led to a significant reduction of virulence (20). So far, the precise function of IbeA has remained elusive and controversial, as some authors suggest it could be an adhesin, while our studies have shown no such role in APEC strain BEN2908 (9,59,60).…”

“…In fact, an ibeA mutant is less adhesive to human brain microvascular endothelial cells (HBMECs) than the wild-type BEN2908, and this feature is correlated with a decrease in type 1 fimbria expression (9). However, this observation is unlikely to explain the decrease in virulence for chickens of an ibeA mutant, as a derivative of strain BEN2908 lacking the entire type 1 fimbria operon is still virulent (39).…”

“…We had previously shown that, in strain BEN2908, the expression of type 1 fimbriae was decreased in the BEN2908 ⌬ibeA mutant (9). It was therefore possible that the increased resistance observed when ibeA is expressed in trans in E. coli K-12 MG1655 is linked to a metabolic alteration due to a modification of type 1 fimbria expression.…”

“…We previously observed that IbeA contains a putative FAD binding domain (E value, 6.8 eϪ06; http://pfam.sanger.ac.uk/) and is predicted to be located in the cytoplasmic fraction of E. coli (9). A more recent search indicated that IbeA belongs to the Pfam12831 protein family, which are annotated as FAD-dependent oxidoreductases (E value, 3.06 eϪ83; http://www.ncbi.nlm .nih.gov).…”

Sequencing and Functional Annotation of Avian Pathogenic Escherichia coli Serogroup O78 Strains Reveal the Evolution of E. coli Lineages Pathogenic for Poultry via Distinct Mechanisms

“…Flagellin contributes to persistence and invasion after oral dosing of chicks with APEC O78 (28), and ExPEC invasins (Ibe proteins) also facilitate APEC invasion (35,36). Indirect effects on the expression of virulence-associated fimbriae have been reported for mutants with a constitutively activated pho regulon (37) and those lacking the pst system (38), ibeA, ibeB, and ibeT (36,39), the barA-uvrY-encoded two-component sensory system (40), and a type VI protein secretion system (41). These reports may partially explain the attenuation of such mutants in chickens and indicate that the effect of mutations may propagate through complex networks.…”