Production of Shiga Toxin and Other Cytotoxins by Serogroups of Shigella

Abstract

We measured the cytotoxic activity of 119 strains of Shigella by using a quantitative [³H]thymidine-labeled HeLa cell assay. We assayed 13 strains of Shigella dysenteriae 1; 18 strains of S. dysenteriae types 2 and 3; and 88 strains of Shigella sonnei, Shigella flexneri, and Shigella boydii. Strains of S. dysenteriae 1 demonstrated high levels of cytotoxicity (geometric mean, 10^5.04 CD₅₀/mg of protein; range, 10^3.95–10^6.10). Cytotoxic activities of the non-type 1 strains of S. dysenteriae and of the other Shigella serogroups were ∼1/1,000 that of the S. dysenteriae 1 strains (range, 10^1.09–10^3.11 CD₅₀/mg of protein). Neutralization of cytotoxicity by using rabbit antiserum to purified Shiga toxin revealed that in all strains of S. dysenteriae 1, ⩾99.5% of cytotoxic activity was attributable to Shiga toxin. In contrast, 88 of the other Shigella strains produced only nonneutralizable cytotoxic activity. Six of 18 strains of non-type 1 S. dysenteriae and 12 of 88 strains from other Shigella serogroups produced both Shiga toxin and nonneutralizable toxin.