Effects of culture conditions on yield of Shiga-like toxin-IIv from Escherichia coli.

The effects of selected culture conditions on production of Shiga-like toxin-II variant by an edema disease strain of Escherichia coli (412) and E. coli TB1 (pCG6) containing the cloned genes for Shiga-like toxin-II variant were examined. Incubation time, culture media, incubation temperature, starting pH of the culture medium, aeration, static culture, anaerobiosis, carbon sources, amino acids, antibiotics, and mitomycin C were investigated. The study showed that Shiga-like toxin-II variant was primarily cell associated and that strain TB1 (pCG6) produced as much as 100 times more toxin than did strain 412. Culture conditions that resulted in the greatest yield of Shiga-like toxin-II variant were incubation at 37 degrees C for 24 h with shaking in syncase broth initially adjusted to pH 8.5. Aerobic culture with shaking resulted in higher yields of Shiga-like toxin-II variant than did static aerobic or anaerobic culture. Addition of various carbon sources or amino acids, or tetracycline, lincomycin, or trimethoprim:sulfadoxine did not increase yields of toxin. The amount of Shiga-like toxin-II variant in supernatant preparations from strain TB1 (pCG6) was significantly increased by addition of mitomycin C to the culture medium.