Figure 6. The VirS/VirR TCRS controls the intestinal virulence of type C strain CN3685. (A) Histologic damage in rabbit small intestinal loops challenged for 6 h with sterile control broth (top left), washed cells of wild-type CN3685 (top right), an isogenic virR null mutant (bottom left) or a virS/virR complementing strain (bottom right). Tissues were processed by histology and stained using hematoxylin and eosin. Sections were photographed at 200 × final magnification. (B) Fluid accumulation in small intestinal loops after challenge with the indicated strains. The asterisk indicates statistically significant (p < 0.05) differences from CN3685. (C) western blot analysis of in vivo CPB production in luminal fluids recovered from small intestinal loops challenged for 6 h with washed cells of each indicated strain. The 35 kDa size of purified CPB is indicated to the left of the blot. Reproduced with permission from ref. 61.