Physiological Characteristics of Lactic Acid Bacteria Near the Maximum Growth Temperature

Abstract

Little information is available on the growth and activity of bacteria at temperatures above the optimum, despite the fact that in many commercial processes the organisms used are often subject to temperatures higher than those most favorable for growth. In the manufacture of Swiss cheese, for example, starter cultures must not only survive the high temperatures used during cooking of the curd, but also must grow at temperatures close to their maximum for several hours. Preliminary investigations have indicated that rates of enzyme production and destruction and of enzyme activity were affected differently by growth at optimum temperatures and at those near the maximum for the organism. It was believed that investigations of the physiological activ-ities of bacteria at near their maximum growth temperatures would add significant information to that regarding these activ-ities at optimum temperatures. Barber (1908), using single cell isolations, studied the rates of multiplication of Escherichia coli at different temperatures. From the minimum temperature of about 10'C., the rate of multiplica-tion increased rapidly as the temperature was raised to 37.50C., IThis work was aided by a grant from the wisconsin Alumni Research Foundation. 2 Published with the consent of the Director of the Agricultural Experiment Station. 479 ROBERT M. STERN AND W. C. FRAZIER where a minimum generation time of less than 17 minutes was reached. From 37.5 to 450C. the rate remained relatively con-stant, then fell rapidly, until at 500C. no growth was evident. Lane-Claypon (1909), working with Escherichia coli, Salmonella enteritidis, and Eberthella typhosa, studied their growth from 20 to 500C. The generation time decreased as the temperature rose to 420C., and then increased from 42 to 5000. Above 50°0. a diminution in numbers of organisms instead of an increase was noted. Slator (1906) studied the ratio between constants of rate of growth at two temperatures and recorded these quotients for every 1000. rise in temperature (Qlo). With yeasts the values