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 hea t shock (50 degrees C), cold shock (4 degrees C) and nisin, respective ly. 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 probable number method. Dur ing heat shock treatment, a 90% decrease of initial population was mea sured 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 coolin g at 4 degrees C. After nisin addition up to 70% of the cellular potas sium was lost within 5 min. These potassium losses led to a transmembr ane pH gradient decrease, but not to cell death at 50 IU ml(-1) of nis in. Increasing the nisin concentration to 200 IU ml(-1) resulted in a decimal reduction of 2.62. (C) 1998 Elsevier Science B.V.