Diversity among verotoxin-producing Escherichia coli O103:H2.

摘要

The objectives of the research were to identify and characterize VTEC in the feces of Ontario beef cattle and to characterize in detail strains of a selected non-O157 VTEC serotype. Cultures of rectal feces from 500 cattle were screened for verotoxin (VT) by ELISA and PCR for genes for verotoxins (vt1 and vt2) and intimin (eae). A VT-immunoblot was used to isolate VTEC from VT-ELISA-positive samples. Prevalence rates of VTEC by VT-ELISA and PCR were 10.2 % and 6.2 %, respectively. VTEC isolated from 27 of 51 VT-ELISA-positive samples belonged to 24 serotypes, five (20.8%) had vt1 only, 19 (79.2%) had vt2 either alone (3) or in various combinations with vt1, vt2c, vt2d; and two (8.3%) were eae-positive. The distribution of selected putative virulence genes was: ehxA, 62.5%; espP, 45.8%; saa, 66.6%; subA, 54.1%. Nine isolates were resistant to antimicrobials.;VTEC of serotype O103:H2 of bovine and human and of North American and European origins were selected for detailed characterization. Ninety-three O103:H2 VTEC strains were characterized by virulence genes, pulsed-field gel electrophoresis (PFGE), plasmid profiling, phenotype, antimicrobial resistance and VT production. All strains were positive for vt1 and eae and 94.6% posessed ehxA. Two strains carried vt2. PFGE differentiated 68 profiles grouped in six clusters and there were 25 plasmid profiles. The proportions of strains with katP and etp genes were significantly higher in European compared to North American human strains. All strains carried genes Z4326, Z4332 and Z4333 and 32.2% carried Z4321. Genes terC, iha and ureC were present in 66.6%, 44.08% and 67.7% of strains, respectively. The distribution of selected phenotypes was: EHEC-hemolysin, 95%; alpha hemolysin, 2%; tellurite resistance, 67%; urease, 1.%; colicin production, 38%; antimicrobial resistance, 57%. VT1 concentrations were significantly increased in low iron cultures. Phages were induced by UV irradiation but not by mitomycin. Thirty-two VT1-phages and two VT2-phages were isolated from 33 strains and belonged to 22 RFLP phage subtypes. All phages carried the Q and P genes and 21/34 produced an amplicon for the Q-stxA1 region. The proportion of human strains that yielded phages (22/48) was significantly higher than that of cattle strains (10/45) (p = 0.02).