Abstract
Ninety strains of low, medium and high temperature bacteria obtained from milk and dairy products or laboratory stock cultures were investigated for determination and evaluation of temperature relations for growth under a temperature gradient incubation. Average values of optimum temperature for growth of low, medium and high temperature bacteria were 28.4, 37.4 and 46.5°C, respectively.
In an attempt to classify the bacteria used, all the strains were divided into seven groups (group I-VII) on the basis of optimum and maximum growth temperatures, and are as follows: true psychrophiles, mesotrophic psychrophiles, psychrotrophic mesophiles, true mesophiles, thermotrophic mesophiles, mesotrophic thermophiles and true thermophiles. There was generally a definite relation between the group classified and the genus of bacteria identified.
Temperature width of growth colony zone of bacteria when incubated for 24 hr under a temperature gradient, was narrow in psychrophiles and broad in thermophiles. The velocity of the spreading colony zone or growth curve under the temperature gradient incubation was discussed to some extent.
