Fig 3. Cytotoxic activity (dilutions 10−¹ to 10−⁶) of culture supernatant isolates of E. coli O157: H7 in Vero cells (A) and CD50 table (B).

A:-induced cytotoxicity was observed with the analyzed supernatants at different dilutions. The results are expressed as percentage of detected neutral red (± 1 SEM); a 100% represents cells incubated without supernatant (control viability). DH5α strain represents a control devoided of Stx activity. Each assay was performed in triplicate, whereas each viability control was assessed by sextuplicate. a letters denoted statistically significant differences (p< 0.01) between the cytotoxic activity of E. coli O157:H7 7.1 Anguil and the rest of the strains in given dilution point. Only the closest point is marked as the other strains with lower activity has as expected also significantly lower activity B: CD50. The results are expressed as the required dose value of culture supernatant to present a Vero cell cytotoxicity of 50%. 100% represents cells incubated without supernatant (control viability). * = P <0.05.