Toxin Production by Clostridium Botulinum in Media at pH Lower Than 4.6

Clostridium botulinum types A and B were able to produce toxin in media containing high concentrations of proteins at pH well below 4.6. A medium containing 15% pork, 0.5% yeast extract, 0.5% glucose and 0.05% cysteine-HC1 at an initial pH between 4.30 and 4.36 produced a toxic sample in as early as one week of incubation at 30 C. Toxin production occurred only when large amounts of precipitated protein were present. The presence of other microorganisms was not required for botulinal toxin production. Media prepared with hydrolyzed protein did not have precipitates and did not support production of botulinal toxin at pH lower than 4.6. Since large amounts of precipitated protein seemed necessary for botulinal toxin production, the possibility of the presence of small, localized pockets of higher pH values within the matrices of precipitated protein could not be ruled out.