Isolation of Shiga toxin-resistant Vero cells and their use for easy identification of the toxin.

Shiga toxin-resistant Vero cells were isolated by treatment of the cells with nitrosoguanidine. These mutant cells were not affected by Shiga toxin at more than 1 microgram/ml, although the parent Vero cells were sensitive to 25 pg of the toxin per ml. Immunofluorescence studies showed that all the mutant cells had lost toxin-binding capacity. The cytotoxic activities of various bacterial cultures against the parent and mutant cells were compared. All samples from 10 strains of Shigella dysenteriae type 1 and all three strains of Escherichia coli O157:H7 tested showed cytotoxicity to the parent cells but not to the mutant cells. Samples from other organisms, such as Shigella flexneri, Shigella sonnei, Clostridium difficile, Aeromonas hydrophila, Aeromonas sobria, and other E. coli strains, either had no effect or were cytotoxic on both the parent and mutant cells. Thus, these mutant cells could be used to identify Shiga-like toxin and distinguish it from other cytotoxins. The results also suggest the presence of a receptor for Shiga-like toxin on Vero cells that is essential for expression of the cytotoxicity of Shiga toxin but is not essential for growth of Vero cells.