THE PRESERVATION OF BACTERIA

Abstract

The method of centrifugal vacuum freezing together with the use of a drying medium consisting of three parts serum, one part broth, and 7.5% glucose has been shown to be suitable for preserving bacteria in the dry state. The method, however, demands a very rapid speed of evaporation and this may lead to contamination of the apparatus and even cross-contamination of cultures. Also, since the temperature of drying is not very low the choice of drying medium is restricted because of the frothing of many media that would otherwise be suitable. To overcome these difficulties an apparatus was designed for drying at a temperature below -30oC With this apparatus a highly effective drying medium containing no protein can be used. The drying medium recommended for use with this apparatus consists of equal parts of 10% dextran and 12% peptone, to which is added glucose 7.5% (w/v) and a detergent "Triton W.R. 1339", 1/4000 (w/v).