Detailed studies of the microbiological population of the soil have revealed not only the presence of numerous actinomycetes but also the fact that the growth of certain of these organisms exerts a depressive effect upon the growth of other microorganisms, notably bacteria and fungi. Casual observations of cultures of actinomycetes isolated by Gasperini from 1892 to 1895, Müller in 1908, Greig-Smith from 1911 to 1917, Lieske in 1921, Gratia and Dath from 1924 to 1927, and Rosenthal in 1925 further demonstrated that these organisms have the capacity to produce chemical substances, now known as antibiotics, which inhibit the growth of other organisms. That these observations were not isolated instances but were characteristic of a large number of the actinomycetes was also established in the various surveys carried out by a group of Russian investigators from 1935 to 1939.
Systematic investigations of the effect of actinomycetes upon other soil organisms, carried out in our own laboratories since 1935 (Waksman, 1937, 1941, 1947), resulted in 1940 in the isolation, in crystalline form, of a pigmented antibiotic which was named actinomycin. This was followed by the isolation in our laboratories of streptothricin in 1942, micromonosporin and streptomycin in 1943, grisein in 1946, neomycin in 1948, and later of a number of other antibiotics, notably streptocin, ehrlichin, fradicin, candicidin, and candidin. Some of these antibiotics, especially streptomycin and neomycin, have found extensive practical application in the control of numerous human, animal, and plant diseases; more recently actinomycin was shown to possess activity against certain forms of cancer; candicidin and candidin give promise as antifungal agents. Nearly all of them are of scientific interest. Numerous other antibiotics soon were isolated in various other laboratories throughout the world.
In recent years, the field of antibiotics has undergone spectacular developments. The ever growing importance of these compounds in the control of human and animal diseases as well as of certain plant diseases, in animal nutrition, in food preservation, in the preservation of biological materials, and in other fields of human endeavor has revolutionized medical practice and many of the habits of modern life. The antibiotics have added untold wealth to our economy and have resulted directly in the prolongation of millions of human lives. They have also introduced a new concept in our understanding of microbial life in natural environments and have added greatly to our understanding of certain chemical reactions in biological systems.
These developments in the field of medical science and the important practical applications in agriculture are due primarily to specific biological and chemical properties of the antibiotics, particularly their antimicrobial activities. Among these, their selective destructive action against various microbial pathogens and their relative harmlessness to the hosts attacked by the pathogens are of particular significance. Antibiotics affect various microbes at different rates. They are not generalized antiseptics and disinfectants. Each antibiotic is characterized by a selective antimicrobial spectrum, or the ability to inhibit the growth of or destroy certain microbes but not others. The various microbes differ, moreover, in the degree of their sensitivity to each antibiotic. On prolonged contact with a given . . .