SUMMARY: Working details are given for keeping as desiccates a collection of some 1500 strains of bacteria. The efficacy of drying, the various methods of freezing, and the effect of storage were tested by viable counts, using a spinning bottle modification of the roll-tube method. The survival rate of bacteria suspended in broth or other protective colloids, and subjected to freezing at −78°, varied with the species from about 100% with the resistant to about 10% with the sensitive , and from about 100 to 1·5% or less, respectively, when the organisms were suspended in saline. The percentage of organisms which survive the freeze-drying process was found to vary with the species, from 100 % to less than 1·0% when the organisms were suspended in broth and from 100 to no survivors when the organisms were suspended in saline. The storage loss of dried cultures was found to be a function of the storage temperature; however, suitably dried cultures could be kept at room temperature for very long periods. By far the most important factor influencing loss on storage was the presence of traces of moisture, and to ensure optimal survival the cultures must be as dry as possible. It appears that even with adequately dried cultures the presence of oxygen is deleterious.

The survival rate of bacteria in a sample of dried culture after heating to 80° for 1 hr., determined by plating a suspension of the heated sample in broth, provides a simple measure of the capacity of the particular batch of the dried culture to remain viable on storage at ordinary temperatures.


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