Virulence-associated genes in avian pathogenic Escherichia coli (APEC) isolated from internal organs of poultry having died from colibacillosis

Escherichia coli infections are responsible for significant losses in the poultry industry in many parts of the world. The pathogenesis and the role of virulence factors are not yet totally elucidated. We, therefore, examined 150 E. coli strains isolated from visceral organs of poultry having died from colibaciliosis for the presence of virulence-associated genes by PCR. The E. coli strains were investigated for the presence of a total of 17 virulence-associated genes described for diarrheagenic (stx1/2, eae, hlyEHEC, estI, eltl, astA, cdtb), septicemic (hlyA, papC, cnf1/2, fyuA, irp2) and avian pathogenic E. coli (APEC; iucD, tsh, fimC, and hlyE as well as stx2f) Seven genes were significantly distributed among APEC strains, while most of the other investigated genes could be demonstrated only sporadically or not at all. FimC (Type I fimbriae) was detected with the highest prevalence in 92.7% of the isolates. Most of the strains harboring iucD (88.7%) also gave positive results for tsh (85.3%). Genes fyuA (ferric yersiniabactin uptake) (66.0%) and irp2 (iron-repressible protein) (68.0%), necessary for Yersinia to acquire iron in the mouse infection model, were regularly detected in combination. Moreover, we found papC (pyelonephritis-associated pili) in 30.0% and astA (enteroaggregative heat stable toxin) in 17.3% of the field strains. A significant amount of strains (57.3%) harbored a combination of iucD, tsh, fimC, fyuA and irp2 virulence-associated genes, presumably rendering these strains particularly virulent. These findings provide novel insights into the presence and distribution of virulence-associated genes in avian pathogenic E. coli field strains, which will help to more comprehensively characterize APEC in future epidemiological studies. It is assumed that the existence of two iron acquisition systems points towards their important role in virulence. Furthermore, we suggest that characterization of the respective phenotypes in infection models will provide substantial information to better understand the pathogenesis of colibacillosis in poultry.