Some Factors influencing the Survival of Bucterium coli on Freeze-drying

SUMMARY: Quantitative studies have been carried out on the survival of bacteria on drying from the frozen state. Attention has been confined mainly to one species of vegetative bacteria, viz. Bucterium coli, of which several different strains were examined. When suspended in a phosphate buffer (pH 7·6) and dried from the frozen state (−35), it was found that the percentage of organisms surviving varied widely with the strain used. With a given strain, it was found tht a well-defined relationship existed between the concentration of organisms in the suspension before drying and the percentage of viable survivors recovered after reconstituting the dried product; the more dilute the suspension thelower the percentage of organisms surviving. When a low concentration of organisms was suspended in the cell-free Altmte obtained from a higher concentration of the same organisms, the percentage of viable organisms recovered approximated to the figure to be expectedfor the higher concentration of organisms. The dependence of percentage survival on the concentration of organiamS in the suspension being dried was shown to be due to soluble material derived from the organisms themselves. On freezing alone, percentage survival wasindependent of the concentration of organisms in the suspension; the material affords protection during the drying stage of the process only. The protective effect of the material during freeze-drying was enhanced by the addition of glucose, especially during prolonged secondary drying.