SUMMARY : In developing a technique for the freeze-drying of lactobacilli particular attention was paid to the percentage survival rate; this was estimated by viable counts immediately after drying and after storage of the dried cultures. Themain factor influencing survival rate was the suspending medium, the best results being obtained in horse serum with 8 % added glucose. Forty-four cultures, fourteen freshly isolated, representative of a comprehensive collection of 452 lactobacilli (see Briggs, 1 9 5 3~) were freeze-dried in this vehicle using the apparatus and technique described. The majority of the survival rates were over 50 yo immediately after drying, and over 25 % after 6 months storage ; all but two of the freshly isolated strains dried well. Some of the dried cultures were tested again after a storage period of about 2 years and then showed satisfactory percentage survivals.For taxonomic studies of 452 strains of lactobacilli (Briggs, 1953a) cultures were maintained in yeast glucose litmus milk plus chalk at 4 O , which, although satisfactory for survival, involved considerable expenditure of media and labour; a less cumbersome method of maintenance was required, and the possibilities of freeze-drying were investigated.Since no outstanding method for lactobacilli had been described, the technique which had proved satisfactory for the freeze-drying of streptococci at this Institute was examined. The effects of different methods of preparing the culture, of various suspending media and of other modifications of the freezedrying technique were studied by determining the percentage survivals immediately after drying and at intervals during storage. A freeze-drying technique was evolved using as test organisms strains of lactobacilli particularly sensitive to drying. The method was then applied to forty-four cultures representative of the eight groups of Briggs (1953a), including fourteen freshly isolated strains, METHODSIn studying the conditions affecting the viability of lactobacilli during freezedrying and subsequent storage, the different factors involved were varied one by one. Deviations from, or comparisons with, the standard method described below are recorded in the appropriate places.Apparatus. The apparatus, illustrated in P1.
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