Atypical Virulence Factors in Enterohemorrhagic Escherichia coli Strains from Bovine Origin.

LARZÁBAL M; VILTE DA; IRINO K; CATALDI AA; MERCADO EC

Melbourne

Congreso; VTEC2006; 2006

  Atypical Virulence Factors in Enterohemorrhagic Escherichia coli Strains from Bovine Origin Mariano Larzábal1; Daniel A Vilte1; Sabrina Rodríguez1; Kinue Irino3; Ángel A Cataldi2, Elsa C Mercado1 1Instituto de Patobiología and 2Instituto de Biotecnología, Instituto Nacional de Tecnología Agropecuaria, Castelar,  Argentina; 3Instituto Adolfo Lutz, Sao Paulo, Brazil Cattle are the most important source of infection by Shiga toxin-producing E. coli (STEC) to humans, causing enteritis and hemolytic uremic syndrome (HUS). Additional virulence factors, such as intimin (eae) and enterohemolysin (ehxA) genes are present in the highly virulent enterohemorrhagic E. coli (EHEC) strains. Although HUS has been reported in patients with E. coli urinary tract infection, little is known about the presence of genetic markers of STEC or  extraintestinal pathogenic E. coli (ExPEC) in the strains isolated. The aim of this research was the genetic characterization of 35 STEC strains isolated from diarrheic (n=27) or healthy (n=3) calves, or bovine meat (n=5). The stx2 and eae subtypes were discriminated by PCR-RFLP. Genes codifying for different toxins (ehxA, cdt-III, cdt-IV, cnf1, cnf2 and astA), adhesins (afaE-8, f17A, sfa, pap and clpG) and siderophores (iucD) were detected by PCR. Expression of F17 fimbriae were investigated by immunogold electron-microscopy. The O and H serotyping were performed by standard methods. Most of the strains (n=27) belonged to seropathotypes frequently associated with HUS. Serotypes O157 (n=6), O5:HNM (n=5), O26:HNM (n=1), O26:H11 (n=6), O111:HNM (n=8) and O145:HNM (n=1), toxin type 2 variants stx2 (n=11), stx2-vhb (n=2) and stx2-vha (n=1), eae (n=32) and ehxA (n=35) were identified among the analyzed strains. Interestingly, some of the strains showed VF characteristic of diarrheagenic E. coli (astA) or ExPEC (cdt-III, iucD, f17A, pap) strains. All the f17A positive EHEC strains expressed F17 fimbriae. Virulence genes (cnf2, afaE-8) mainly linked to bovine E. coli strains, were also detected. The epidemiological role of EHEC strains with virulence traits of ExPEC pathotype, and its association with cases of HUS following extraintestinal infections, needs to be further evaluated. Key words: enterohemorrhagic Escherichia coli, extraintestinal virulence factors, cattle.