NATURE OF ANTIBIOTIC SUBSTANCES 125 



One of the important cultural characteristics of the production of 

 streptomycin is the need for a specific substance in the medium, as found 

 in meat extract, corn steep, or the mycelium of the actinomyces. On a 

 medium containing sodium nitrate or an amino acid as a source of nitro- 

 gen, the organism produces good growth but little antibiotic activity. 

 However, when the mycelium thus formed in the culture is added to 

 fresh medium, streptomycin production takes place. This indicates that 

 the organism is capable of synthesizing the streptomycin "precursor," 

 but not in sufficient amounts to influence the production of the antibiotic 

 in the culture. For rapid and abundant formation of streptomycin, the 

 presence of a "precursor" in the medium is required. The presence of a 

 small amount of carbohydrate, such as glucose, is also favorable to 

 growth and the production of the streptomycin. The reaction of the 

 medium changes first to acid and later to alkaline, the highest alka- 

 linity (^H 8.2 to 8.6) corresponding to the maximum production of 

 the streptomycin. When the culture begins to undergo lysis, there is 

 another increase in acidity of the culture, accompanied by an increase in 

 viscosity, due to the formation of slimy material. 



Growth and activity reach a maximum in stationary cultures in 8 to 

 10 days, at 28° C, and in submerged cultures in 2 to 3 days. The latter 

 depends largely on the nature and amount of inoculum: with a heavy 

 inoculation of pregerminated spore material the maximum may be 

 reached in 36 to 48 hours. 



Streptomycin is produced only by certain strains of S. griseus. Even 

 the active culture may gradually deteriorate (832) due to the forma- 

 tion of inactive strains or spore-free variants, which are unable to form 

 the antibiotic. For the successful production of streptomycin, it is essen- 

 tial, therefore, continuously to select active strains from the mother 

 culture. 



The streptomycin is found in the culture filtrate, from which it can 

 be isolated by suitable methods. However, the mycelium of the organ- 

 ism appears to contain small amounts of a second antibiotic factor which 

 is soluble in ether, and which has a bacteriostatic spectrum distinct from 

 that of streptomycin. This second factor has not been sufficiently 

 studied. 



A'', gardneri produces an active bacteriostatic substance that has been 



