When pH was controlled during the growth of C. perfringens type C there was an increase in toxin but not in cells. The increases in toxin over that obtained at uncontrolled pH were 3-, 20-, 70-, and 4-fold, for alpha, beta, delta, and theta toxins respectively. pH control did not increase the yield of kappa toxin. Optimum pH was 6.7 for alpha, 7.5 for beta and theta, and 7.5–8.0 for delta. The maximum yields of toxins at optimum pH were 90 MLD of alpha, 100,000 MLD of beta, 2000 hemolytic units of delta, and 4000 hemolytic units of theta. Mu and nu toxins were not produced by the strain of type C used.

A strain of Clostridium perfringens type D was grown in a complex medium with or without pH control. Rate and extent of growth was the same without pH control and at controlled pH levels between 6.0 and 7.4, but was reduced at pH 7.6. With controlled pH at optimum levels the yields of alpha, epsilon, kappa, and theta toxins were 2, 6, 2, and 8 times higher than without pH control. These yields were 25 MLD, 70 × 103 MLD, 400 kappa units, and 60 hemolytic units per milliliter respectively. Optimum pH was 7.0 to 7.2 for alpha, 6.7 to 7.4 for epsilon and kappa, and 7.0 to 7.4 for theta toxin. Lambda and mu toxins were not produced, and only traces of nu antigen were formed.Fourteen additional strains of C. perfringens type D were grown with pH controlled at 7.0 or without pH control and assayed for production of epsilon, kappa, and theta toxins. Epsilon was formed by 14, kappa by 10, and theta by 13 strains. With pH controlled at 7.0, 14 strains produced more epsilon toxin, 4 strains more kappa toxin, and 10 strains more theta toxin than without pH control. It is concluded that increased toxinogenesis at controlled pH is a general phenomenon in cultures of C. perfringens type D.