Minimal Growth Temperature, Sodium Chloride Tolerance, p H Sensitivity, and Toxin Production of Marine and Terrestrial Strains of Clostridium botulinum Type C

Abstract

Minimal growth temperatures of four marine and two terrestrial strains of Clostridium botulinum type C were determined in a laboratory culture medium, fortified egg meat medium (FEM), and in ground haddock. The inoculum equaled 2 × 10 6 viable spores per tube with five-tube replicate sets. The spores were preheated in aqueous suspension at 71 C for 15 min prior to inoculation to reduce toxin carry-over. Similar results were obtained in both substrates. Both the marine and the terrestrial strains grew at 15.6 C, but only the terrestrial strains grew at 12.8 C. None of the strains grew at 10 C during prolonged incubation. The sodium chloride tolerance and the p H sensitivity of the marine and the terrestrial strains were determined at 30 C. The basal medium consisted of beef infusion broth. The inoculum level equaled 2 × 10 6 unheated spores per replicate. Growth was inhibited at salt concentrations from 2.5 to 3.0%. The terrestrial strains were more p H-sensitive than the marine strains. Whereas the terrestrial strains failed to grow below p H 5.62, three of the marine strains grew at p H 5.10, but not at p H 4.96, during extended incubation. One marine strain grew at p H 5.25, but not below. FEM and proteose peptone-Trypticase-yeast extract-glucose medium permitted the production of high levels of botulinum toxin among four media tested. Toxin produced by the marine and terrestrial strains showed no increase in toxicity after incubation with trypsin.