MAINfENANCE AND PRESERVATION OF CULTURES 107 



Table 13. Maintenance Methods (American Type Culture Collection) 



{Continued) 



* Plus sign indicates successful preservation by this method, + + that the organism in question should 

 preferably be kept lyophilized; minus sign that lyophilization is unsuccessful or not tried at ATCC. 



t Tryptone-glucose-yeast medium (No. 35) as used by the Northern Regional Research Laboratory, 

 U.S. Department of Agriculture, may be substituted. 



X The optimum temperature for some species is different; consult Bergey's Manual. 



§ A special medium is required by certain species. 



il Some strains are favored by the addition of CaCOs to this medium. 



below 0°C are sometimes employed for long-term preservation of bac- 

 terial cultures, including some that are not amenable to dry methods of 

 storage. The principle involved is similar to that applied in quick freez- 

 ing of food products, red blood cells, spermatozoa, and vital tissues. 

 Relatively little is known as yet about the effect of subfreezing tempera- 

 tures on the viability of bacterial cultures, including such factors as 

 minimum temperature that is tolerated and duration and rate of freezing. 

 The available information is reviewed in references cited at the end of 

 this chapter. 



Since essentially aqueous solutions or emulsions such as broth and agar 

 become solid at these temperatures, often with rupture of glass containers 

 even if the organisms survive, some means of counteracting the physical 

 effect of ice formation is desirable. Hollander and Nell (1954) have sug- 

 gested the use of 15 per cent glycerol to accomplish this purpose. In 

 general, it appears that moderately low temperatures, as —10 or — 20°C, 

 have been more favorably regarded for the preservation of bacterial 

 cultures than lower or higher subfreezing temperatures. There are few 

 conclusive data, however. 



