Protective Effect Of Glutamic Acid And Related Compounds On Bacterial Cells Subjected To Freeze-Drying

Abstract

In order to increase the survival ratio immediately after the freeze-drying of bacterial suspension and to minimize the death rate of dried organisms during storage, the choice of an appropriate suspending medium is a matter of importance. Most of the suspending media commonly used have been the solutions of complicated substances such as proteins and polysaccharides. Use has also been made of complex natural materials such as immunologically inactivated serum, skim milk or nutrient broth. MILLER et al. (1) demonstrated that some compounds of low molecular weight, such as sodium glutamate and aspartate protected Bacille Calmette-Guerin (BCG) during freeze-drying. OBAYASHI et al. (2, 3, 4) showed that a dried BCG vaccine prepared with sodium glutamate solution as suspending medium remained biologically and allergenically stable during storage at a temperature as high as 37°. In a field trial undertaken jointly by Tuberculosis Research Office of World Health Organization and Research Institute of the Japan Anti-tuberculosis Association (5), these vaccines could be maintained for as long as 30 days at a tropical temperature without showing any marked loss of allergenic potency. OTA (6) and OBAYASHI et al. (7) reported that the use of sodium glutamate solution as a medium for freeze-drying of Lactobacillus bifidus significantly enhanced the stability of the dried organisms. KOZTMA et al. (8) demonstrated that freeze-dried organisms as inocula for microbiological assays (Latobacillus arabinosus, Leuconostoc mesenteroides and Streptococcus faecalis) could be greatly stabilized by sodium glutamate. GREAVES (9) has also drawn attention to this drying medium for gonococcus and paracolon bacillus and found its effectiveness in preserving the viability of these organisms. Despite these extensive studies on the application of glutamate in the process of freeze-drying, the mechanism of its protective effect has remained obscure. The present studies were undertaken to clarify this point with special reference to the relationship between the protective activity and the chemical structures of protectants, using a variety of substances chemically related with glutamic acid. © 1963, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.