Association of enterohemolysin and non-fermentation of rhamnose and sucrose with Shiga-like toxin genes in Escherichia coli from calves.

Fecal Escherichia (E.) coli strains from calves were tested for simply detectable phenotypical features associated with Shiga-like toxin (SLT) genes. DNA hybridization with SLT-specific oligonucleotide gene probes (detection of genes for SLT-I and SLT-II) was the "gold standard" for the evaluation of Vero cell cytotoxicity, fermentation of several saccharides, beta-D-glucuronidase activity and production of alpha-hemolysin (alpha-Hly) or enterohemolysin (E-Hly). While SLTEC and non-SLTEC did not significantly differ in production of alpha-Hly, beta-D-glucuronidase activity and fermentation of D-sorbitol, production of E-Hly and non-fermentation of L-rhamnose (Rha) and D-sucrose (Suc) were associated with SLT genes. Sensitivity and specificity of the E-Hly+ phenotype were 53% and 88% for identification of calf SLTEC. When three markers were combined to form the parameter ["E-Hly+ or (Rha- and Suc-)"], sensitivity was higher (65%) and specificity was almost the same (85%). Production of enterohemolysin and inability to ferment rhamnose and sucrose were more often associated with the SLT-I gene than with SLT-II genes. Approximately 71% SLT-I+ E. coli were positive in the enterohemolysin assay. The test combination "E-Hly+ or (Rha- and Suc-)" and Suc-)" was most valuable for the presumptive identification of SLT-I+ E. coli (sensitivity 85%, specificity 83%). These data suggest that the phenotype "E-Hly+ or (Rha- and Suc-)" may be a helpful marker for the detection of SLT-I+ E. coli in SLTEC associated diarrhoea of calves.