Psychrophilic Bacteria—A Review

Abstract

Psychrophilic bacteria grow at a relatively rapid rate at or below 45° F. (7.2° C.) and are capable of forming visible colonies on plates incubated for ten days at 7 ± 0.5 C. Since psychrophiles grow at refrigeration temperatures, they are primarily responsible for limiting the keeping quality of milk and many dairy products in which they may produce a wide variety of spoilage defects. The psychrophiles most frequently encountered are in the genus Pseudomonas, although many bacterial genera contain psychrophilic species. They are found in water, soil, and dirty equipment, and their elimination from milk and dairy products is largely concerned with removing these sources of contamination. The various factors affecting the survival, growth, enumeration, and biochemical activities of psychrophiles were discussed. The fundamental question of why psychrophiles are capable of growing at low temperatures is still to be answered. Information on these and other aspects of psychrophiles was documented and interpreted with the purpose of summarizing the available information and encouraging further investigation of this important group of microorganisms. © 1961, American Dairy Science Association. All rights reserved.