Prevalence and clinical significance of vero-cytotoxin-producing Escherichia coli (VTEC) isolated from cattle in herds with and without calf diarrhoea.

To determine the clinical significance and prevalence of Vero cytotoxin (VT)-producing E. coli (VTEC) in Swiss cattle, faecal swabs and milk samples of 93 cattle from two farms with calf diarrhoea, and of 54 cattle from two similar farms without clinical problems, were screened for VTEC by PCR and colony-blot hybridization. On average, 21% of all cows were positive for VTEC by PCR, without differences between farms with and without diarrhoea problems. By contrast, VTEC were detected by PCR in 60% of animals younger than 2 years from farms with diarrhoea problems, whereas only 32% of comparable control animals from farms without clinical problems had VTEC. No VTEC were detected in the milk samples. A variety of toxin types, antimicrobial-susceptibility patterns and serotypes were found by colony-blot hybridization, among the VTEC in individual herds. However, there was a significant relationship between the VT1-only toxin type and the presence of antimicrobial resistance and clinical disease in calves. No association could be found between levels of VTEC excretion and the presence of diarrhoea. This is the first study to report systematic quantitative data on numbers of VTEC in faecal samples of cattle positive for VT genes by PCR.