The Preservation of Bacteria by Drying

SUMMARY: A quantitative study of the survival of vegetative bacteria on drying in various suspending media led to a simple method for preserving bacterial cultures. Bacterial cells are suspended in melted nutrient gelatin cont.aining ascorbic acid or sodium ascorbate in concentration of 0·25–0·5%. Small quantities are dried over P2O5 at pressures of 100–300 mm, of mercury and stored in vacuo over P2O5 at room temperature. A wide range of bacterial species of medical and verterinary importance was preserved by this method for 4 years. The slow decline in the number of viable organisms and the high percentage survival rate at 4 years indicate the likelihood of survival for a much longer period. The virulence of a number of pathogenic species was successfully maintained in the dry preparation. The method might well be applied to the preservation of living vaccines. The survival rates with Chromobacterium prodigiosum dried by this method were better than those in preparations subjected to rapid freeze-drying processes. They were, however, unsatisfactory with a few species such as Vibrio cholerae and Neisseria meningitidies.