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 O1 57 strains isolated from 37 asymptomatic human carriers yielded two strains with stx2, 10 strains with stx2c and 24 strains with stx2d genes. One isol ate harboured stx2 and stx2c. The high Stx2d prevalence in asymptomatic car riers was conspicuous and may indicate a reduced pathogenicity of these tox in variants. Therefore, in order to appraise a positive STEC laboratory res ult, the strain must be isolated in every case. Shiga toxin types and furth er virulence-associated factors have to be investigated.