The Distribution of Soil Microorganisms Antagonistic to Fungi Pathogenic for Man

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Abstract
Various soils were studied. Methods of random isolation and selective plating were employed to isolate the antagonists. The agar streak method in which 3 media were employed, the agar-dilution and agar-diffusion tests with a glucose-tryptone agar were used to demonstrate the antifungal activity. Candida albicans, Crypto-coccus neoformans, Trichophyton gypseum and T. rubrum (purpureum) were the test fungi. 124 or 51% of 243 acti-nomycetes were found to be antagonistic by the agar streak method to one or more of the 4 test fungi. The data obtained from the selective plating procedures showed that the percentage of antagonistic bacteria was considerably less than that of the antagonistic actinomycetes. On the other hand, the data for soil fungi, although limited, indicated a distr. of antagonistic forms in between the values for bacteria and actinomycetes, probably closer to that of the latter. The assays of culture filtrates of those actinomycetes active by the streak test revealed that 15% of the microorganisms were active by the agar dilution test, whereas 55% exhibited inhibition by the diffusion method. The greater activity by the diffusion assay indicated this to be the more sensitive of the two methods. The nutrient broth was decidedly inferior to the glucose-tryptone and glycerol-yeast extract media for production of culture filtrates with antifungal activity, although the percentage of actinomycetes antagonistic to each of the test fungi was comparable on the 3 agar media. Crypto-coccus neoformans was found to be the most sensitive and Candida albicans the most resistant to the active culture filtrates by the agar dilution procedure.