Influence of Time and Temperature of Incubation on Heat Resistance of Escherichia coli

Abstract

Field and laboratory observations (Frazier et al. 1935) long have indicated that the temperature of incubation of Swiss cheese starter cultures significantly influences their ability to develop following the rather severe heat exposure to which they are subjected during manufacture. If it were true that the temperature of growth had an effect on heat resistance of bacteria, this fact would be of significance in various fermentations, both commercial and natural, and would prove of general interest from the standpoint of the physiology of bacteria. Therefore, an investigation was initiated to determine the influence of incubation temperature and time on the thermal resistance of certain Swiss cheese starter cultures. For the purpose of comparison, similar studies were undertaken with a typical strain (H-52) of Escheri-chia coli. The results of the investigations on E. coli are presented in this paper. Because it produced less acid, was able to develop under a wider variety of environmental conditions, and could be counted fairly accurately by the plate method, E. coli gave results which were more conclusive than those obtained with the lactic starter cultures and indicated that E. coli, a favorite subject for experimentation , is an ideal organism for studies on the heat resistance of vegetative cells.