64 ISOLATION AND CULTIVATION OF ANTAGONISTS 



lidify and small amounts were placed with an inoculating needle in the 

 centers of the agar plates. The plates were incubated at 24° C. for 6 

 days J then 4 or 5 plugs were removed radially from the agar, the first 

 being adjacent to the colony margin, and tested as described above 



(838). 



Various other methods have been proposed for measuring the rate of 

 production or secretion of antibiotic substances by fungi (726, 963). 



METHODS OF GROWING ANTAGONISTIC 



ORGANISMS FOR THE PRODUCTION 



OF ANTIBIOTIC SUBSTANCES 



Once the antagonistic action of any organism has been established, 

 the next step is to determine the nature of the substance produced and 

 to measure quantitatively its antibiotic action. Before this can be done, 

 however, the organism must be grown upon suitable media under 

 conditions favorable for the maximum production of the antibiotic 

 substance. 



The media used for the production of antibiotics can be classified into 

 two groups: synthetic and complex organic media. The first contain a 

 source of carbon, usually glucose, sucrose, or starch (2 to 6 per cent) j a 

 source of nitrogen, usually nitrate or ammonia sulfate (0.2 to 0.6 per 

 cent) ; several salts, namely, K0HPO4 orKHoP04 (o.i to 0.2 percent), 

 MgS04.7H20 (0.05 per cent), KCl (0.05 per cent), and FeS04.7H20 

 (0.00 1 per cent). Certain supplementary materials such as yeast ex- 

 tract, meat extract, or corn steep, or trace elements such as ZnS04, 

 MnS04, or CUSO4 (i to 2 ppm.) may also be added. The organic 

 media contain a complex form of nitrogen, such as tryptone, peptone, 

 casein digest j either no other source of carbon is used or a carbohydrate 

 is added in the form of lactose, glucose, dextrin, starch, brown sugar, 

 molasses, or similar products as well as several salts similar to those 

 listed above. Some media are supplemented with CaCOo, others are 

 not, depending upon the extent of acidity produced by the organism. 



The medium may be solid (agar or bran) or liquid, the latter being 

 the more common. Several types of culture vessels are used, depending 

 on the condition of aeration. Since so far as is known all the micro- 



