Culturability of Clostridium botulinum spores under different germination conditions, sublethal heat treatments, and in the presence of nisin.

摘要

Thermal resistance and heat activation characteristics of Clostridium botulinum ATCC 25763 spores, and effects of nisin and pH on activation and subsequent germination, were determined. Spores of C. botulinum were not inactivated by heating up to 92 degrees C for 2 h. Heating at 85 degrees C for 90 min was selected as the optimum activation temp. based on monitoring subsequent germination. L-alanine alone or in combination with L-cysteine was not sufficient to germinate spores. Tryptone-Peptone-Glucose-Yeast extract (TPGY) broth supplemented with L-alanine was used as a suitable germination medium. Decreasing the pH of activation suspension increased the degree of phase darkening, as did the presence of nisin. The majority of spore populations were dormant at pH <2.8 and required heat activation to increase their culturability on TPGY agar medium. Extended heating in the presence of nisin at pH 2.8 decreased the spore count; however, heating was less necessary at pH 3.4, compared to pH 2.8.