Influence of Potassium Sorbate and Reduced pH on the Growth of Vegetative Cells of Four Strains of Type A and B Clostridium botulinum

Growth of vegetative cells of four strains of Clostridium botulinum was measured as the average A 630nm of five replicate peptone‐yeast extract broth cultures at 37°C. Media pH values ranged from 7.1 to 5.5 and potassium sorbate concentrations of 0 or 0.26%. Growth ratios (GR = treatment/control) based on the time to reach an A = 0.35 were calculated. Predicted GR's from the linear regression of log (GR) vs log (undissociated sorbic acid concentration) were used to compare strains. Reduced pH (>5.5) had minimal effects on GR. Sorbate inhibited the growth of all strains at 250 mg/L undissociated sorbic acid. This was indicated by predicted GR's of 2.3‐3.4. Responses of cells derived from different spore suspensions of the same strain were similar.