CHAPTER 4 



ISOLATION AND CULTIVATION OF 



ANTAGONISTIC MICROORGANISMS^ METHODS 



OF MEASURING ANTIBIOTIC ACTION 



In nearly all the earlier work and even In many recent investigations 

 on the antagonistic properties of microorganisms and the production 

 of antibiotic substances, two procedures were employed: indiscriminate 

 testing of pure cultures of bacteria and fungi, commonly taken from 

 culture collections, for antagonistic effects against one another or against 

 certain specific or test organisms j and isolation of occasional antagonistic 

 organisms from old plate cultures, as air contaminants, or from mixed 

 infections. These studies were carried out either by medical bacteri- 

 ologists interested in agents capable of suppressing bacterial pathogens 

 or by plant pathologists interested in organisms capable of inhibiting 

 the growth of fungi, principally those concerned in the causation of 

 plant disease. They resulted in the accumulation of considerable infor- 

 mation concerning antagonistic organisms, the nature of the phenome- 

 non of antagonism, and, to a more limited extent, the mechanisms in- 

 volved. Neither of these methods, however, is suitable for a systematic 

 study of antagonism as a natural process. 



The last decade has witnessed a number of systematic attempts to de- 

 termine the distribution of antagonists in nature, to isolate specific or- 

 ganisms capable of bringing about the desired reactions, and to estab- 

 lish the mechanism involved in these reactions. These studies were 

 undertaken by a group of Russian investigators interested largely in 

 fungi and actinomycetes as agents antagonistic to other microorganisms 

 chiefly causing plant diseases, and by American and British investigators 

 interested in agents active against bacterial pathogens of man. 



The early significant, but unrecognized, investigations of Schiller 

 (797? 798) on forced antagonisms and the studies of Gratia and his as- 

 sociates (349, 350) on mycolysates were in direct line of the more re- 

 cent studies of Dubos (190), who made a systematic attempt to isolate 

 from specially enriched soils bacteria capable of destroying specific 



