Characterization of shiga toxin type 2 variant B-subunit in Escherichia coli strains from asymptomatic human carriers by PCR-RFLP.

Subtyping of shiga toxin type 2 variant B-subunit in 35 non-O157 and two O157 strains isolated from 37 asymptomatic human carriers yielded two strains with stx2, 10 strains with stx2c and 24 strains with stx2d genes. One isolate harboured stx2 and stx2c. The high Stx2d prevalence in asymptomatic carriers was conspicuous and may indicate a reduced pathogenicity of these toxin variants. Therefore, in order to appraise a positive STEC laboratory result, the strain must be isolated in every case. Shiga toxin types and further virulence-associated factors have to be investigated.