Selective Antibiotic Action of Various Substances of Microbial Origin.

Since Pasteur first demonstrated that certain micro6rganisms are able to exert antagonistic or antibiotic effects upon other organisms, an extensive literature has accumulated (Waksman, 1941). The presence of living organisms is often necessary for the phenomenon of antagonism to take place. In many cases, the antagonist was found to produce an active substance responsible for this action. The active agent has been isolated, purified, and crystallized only in very few instances. Pyocyanase was the first antagonistic substance to have thus been obtained (Emmerich and Low, 1899). Several others have been isolated recently. Certain facts have now become recognized concerning the nature of the phenomenon produced by antagonistic microorganisms: 1. The various active substances isolated from the different organisms vary considerably in their chemical nature; 2. these substances are selective in their action upon various organisms, showing variation even as regards specific types or strains of the different groups of bacteria acted upon; 3. the substances vary in the mechanism of their action, some being primarily bacteriostatic, and others bactericidal but not bacteriolytic, whereas still others are both bactericidal and bacteriolytic; 4. the antagonistic capacity is widely distributed among microorganisms and is not limited to any one group of bacteria or fungi. Active antibiotic agents have now been obtained from representative types of spore-forming bacteria, non-spore-forming bacteria, actinomycetes and fungi. Some of these agents have not yet been isolated in a pure state; however, they are well recognized, both chemically and biologically, and can be characterized by their specific properties. The following substances or preparations have received the greatest consideration: 1. pyocyanase, 2. pyocyanin, 3. gramicidin, 4. tyrocidine, 5. penicillin, 6. gliotoxin, 7. actinomycin, and 8. streptothricin. The first four are of bacterial origin, the next two are produced by fungi, and the last two by actinomycetes. To these may be added several other preparations, of which the exact chemical nature or mode of action is less known, namely, actinomycetin, prodigiosin, fluorescin, microbial-lysozyme, active substances obtained from species of Aspergillus and from various other fungi and bacteria. Among the antagonistic phenomena which are now well recognized but for which no active substance has as yet been demonstrated, one may men-