Prevalence and characteristics of verotoxin-producing Escherichia coli (VTEC) in stool samples from asymptomatic human carriers working in the meat processing industry in Switzerland

A total of 5590 stool samples from healthy employees in the meat industry w ere screened by PCR for verotoxin-producing Escherichia coli (VTEC). The PC R product of VT-encoding genes was detected in 3.5% of the samples. Phenoty pic and genotypic traits of 47 VTEC strains isolated from asymptomatic carr iers were characterized. A variety of serotypes was found; one strain belon ged to the serotype O157:H7. The majority of the isolates proved to be VT2- positive. Fifty-seven percent of the verotoxin-producing strains harboured the genes for one or several additional virulence associated factors, inclu ding intimin (eae, 8.5%), the 60 MDa plasmid (42.5%), enterohaemolysin (EHE C-hlyA, 38.3%), the heat-stable enterotoxin (astA, 6.4%), a serin protease (espP, 6.4%), colicin production (col D157, 12.8%) and a secretion system I I (etpD, 10.6%). None of the strains was positive for a specific enzyme wit h catalase-peroxidase activity (katP).