An Attempt to Increase the Heat Resistance ofMicrobacterium lacticum

摘要

Summary.An attempt to increase the heat resistance of two strains ofMicrobacterium lacticumwas made by exposing cells dispersed on an agar surface to 72° for two different times. Eighteen successive subcultures from survivors gave no increase in the proportion of heat resistant cells. There was no change in the ratio of the percentages of cells surviving the different treatments, an indication that there was no change in the overall heat resistance. With both strains the changing proportions of colonies developing on the 3rd and 5th day of incubation demonstrated the damaging effect of increasing the time of exposure at 72° but did not indicate any increase in heat resistance. The theoretical implications of these findings are discusse