Figure 4. Contact with host Caco-2 cells induces an upregulation of toxin production by C. perfringens. (A) western blot analysis of ETX production by type D strain CN3718 (WT), the isogenic ΔAgrB null mutant (Δ) or the P3 agr locus complementing strain (P3). Shown is ETX production by these strains after 1‒2 h in the presence (Caco-2 cells) or absence (MEM) of enterocyte-like Caco-2 cells. (B) western blot analysis of CPB production by type C strain CN3685 (WT), the isogenic ΔAgrB null mutant (Δ) or the P3 complementing strain (P3) after 2 h in the presence of Caco-2 cells. No CPB production was detected after 2 h growth of these strains in the absence of Caco-2 cells. (C) western blot analysis of CPB production by CN3685, the isogenic virR null mutant (VirR ko) or the VirR/pTS405 complementing strain after 2 h in the presence of Caco-2 cells. Reproduced with permission from refs. 51 and 54.