Vero cytotoxin production and presence of VT genes in strains ofEscherichia coliandShigella

Strains of enteropathogenic Escherichia coli (EPEC), enteroinvasive E. coli (EIEC) and Shigella were examined for Vero cytotoxin (VT) production and tested for the presence of VT genes in DNA hybridisation experiments with specific probes for VT1 and VT2. Twenty seven of 104 EPEC strains produced VT and in 26 of the 27 strains VT genes were detected. The VT+ EPEC strains belonged to serogroups O26, O55 and O128. Strains belonging to 8 other EPEC serogroups including strains isolated from 13 outbreaks, were all negative using both techniques, as were the 5 EIEC strains. It is concluded that VT1 and VT2 are not virulence factors in most EPEC infections. VT1 was demonstrated in all Sh. dysenteriae type 1 strains but neither VT1 nor VT2 were detected in strains of Sh. flexneri, Sh. boydii or Sh. sonnei.