METHODS OF TESTING ANTAGONISTIC ACTION 59 



method, Chudiakov (143) isolated various bacteria antagonistic to 

 Fusarium. The antagonists were found abundantly in cultivated soils, 

 but not in flax-sick soils rich in Fusarium. Bamberg (35) demonstrated, 

 in the soil, bacteria capable of bringing about in 10 days complete de- 

 struction of Ustiliago zeae and other fungi. Myxobacterium was also 

 found (473) capable of bringing about the disintegration of fungus 

 mycelium. Nonspore-forming bacteria, similar to the cultures of 

 Chudiakov, were isolated and shown to be able to attack a number of 

 fungi, including species of Fusarium, Sclerotinia, Gleosforium, Acro- 

 stalagmus, Alternaria, and Zygorhynchus (729). 



METHODS OF TESTING THE ANTAGONISTIC 

 ACTION OF MICROORGANISMS 



Once antagonistic organisms have been isolated, it is essential to es- 

 tablish their bacteriostatic spectrum — that is, their ability to inhibit the 

 growth of various specific microorganisms. Usually these antagonists 

 do not affect alike all bacteria and fungi, some acting primarily against 

 gram-positive bacteria and against only a few gram-negative forms 

 (mostly cocci), others acting upon certain bacteria within each of these 

 two groups. 



A considerable number of methods have been developed for meas- 

 uring these antagonistic effects. They measure the selective nature of 

 the antagonistic action and they can also give quantitative information 

 concerning the intensity of this activity. Because of the great differences 

 in the degree of sensitivity of bacteria to the action of the antagonists, 

 the proper selection of one or more test organisms is highly essential. 

 S. aureus has been employed most commonly, different strains of this 

 organism having been found to vary greatly in their sensitivity even to 

 the same substance. Stre-ptococcus viridans, B. subtilis, Micrococcus ly- 

 sodeikticus, S. luiea, E. coli, and E. tyfhosa are other organisms that 

 are frequently employed for testing the activity of antagonists. Al- 

 though for purposes of concentration and purification of a known sub- 

 stance a single test organism is sufficient, it has been found advisable 

 during the isolation of antagonistic organisms and the study of the na- 



