Effects of temperature shift on acid and heat tolerance in Salmonella enteritidis phage type 4

The transfer of cells of Salmonella enteritidis phage type 4 from 20 to 37-46 degrees C resulted in marked increases in acid and heat tolerance. The former was maximized within 5 to 15 min of the shift and was largely independent of protein synthesis. In contrast, induction of increased heat tolerance was slower, requiring more than 60 min to be completed, and was prevented by inhibition of protein synthesis. When cells were transferred to medium at temperatures between 47 and 50 degrees C, the kinetics of induction of heat tolerance were essentially the same as at the lower temperatures. In contrast, the cells became more acid sensitive. The results of these studies clearly show that although both acid and heat resistance can be enhanced by preexposure to high incubation temperatures, the mechanisms involved are different.