Clostridium botulinum growth and toxin production in tomato juice containing Aspergillus gracilis

The ability of spores of one type A and one type B strain of Clostridium botulinum to grow and produce toxin in tomato juice was investigated. The type A strain grew at pH 4.9, but not at pH 4.8; the type B strain grew at pH 5.1, but not at pH 5.0. Aspergillus gracilis was inoculated along with C. botulinum spores into pH 4.2 tomato juice; in a nonhermetic unit, a pH gradient developed under the mycelial mat, resulting in C. botulinum growth and toxin production. In a hermetic unit, mold growth was reduced, and no pH gradient was detected; however, C. botulinum growth and low levels of toxin production (less than 10 50% lethal doses per ml) still occurred and were associated with the mycelial mat. The results of tests to find filterable or dialyzable growth factors were negative. It was demonstrated that for toxin production C. botulinum and the mold had to occupy the same environment.