Practice 9 - Counting of cold-tolerant microorganisms

Abstract

Psychrophilic and psychrotrophic microorganisms grow at 0°C. Psychrotrophic microorganisms have a maximum growth temperature of 35°C and are widely spread in natural environments and in foods. Psychrophilic microorganisms have a maximum of growth temperature for growth of 20°C and are restricted to permanently cold habitats. Mesophilic microorganisms adapted to low temperatures are called psychrotroph. They increase the proportion of unsaturated fatty acids in the cell membrane lipid phase. This makes the cell membrane more fluid and the protein conformation functional at low temperature. The counting of cold-tolerant microorganisms involves the formation of colonies on an agar medium after incubation at low temperature. Various techniques are used for counting the cold-tolerant microorganisms. Bacteria on selective or nonselective media can also be incubated at higher temperatures for a shorter time.