Rapid cooling, moderate heat treatment and nisin addition influence cell homeostasis of Clostridium perfringens type A.

Vegetative cells of Clostridium perfringens type A were exposed to heat shock (50 degrees C), cold shock (4 degrees C) and nisin, respectively. In all cases, pronounced leaks of cellular K+ were observed. These losses were not systematically related to cell death, as demonstrated by cell viability measurement by the most probably number method. During heat shock treatment, a 90% decrease of initial population was measured within 15 min, and K+ leaks were mainly associated to cell death. A cold shock induced a rapid and large K+ efflux from the cells, at least 50% of the total potassium content. Potassium movements were not associated with internal pH changes, or with cell death during cooling at 4 degrees C. After nisin addition up to 70% of the cellular potassium was lost within 5 min. These potassium losses led to a transmembrane pH gradient decrease, but not to cell death at 50 IU ml-1 of nisin. Increasing the nisin concentration to 200 IU ml-1 resulted in a decimal reduction of 2.62.