ANTIBIOTICS*

Summary 1. The phenomenon of antagonism or antibiosis among micro‐organisms dates back to the early days of microbiology. The early studies made by students of mixed infections, of accidental contaminations of cultures, of the effects of one organism or its metabolic products upon another, of the isolation of such products, and even attempts to utilize them for disease control, all represented a series of unco‐ordinated observations rather than a system which would fit into a new and important branch of science. The new ‘antibiotic age’ dates only to 1938‐9, when a series of co‐ordinated studies were made in several laboratories throughout the world. 2. Antibiotics, known previously as lysins, toxins, lethal principles, staling principles, etc., are characterized by certain important properties which distinguish them sharply from the common antiseptics and disinfectants. They are produced by micro‐organisms, they are selective in their action upon bacteria and other micro‐organisms, they vary in their chemical and physical properties, they differ in their mode of action and are affected differently by the composition of the substrate in which they act, they vary in their toxicity to animals, and, therefore, in their chemotherapeutic potentialities. 3. Antibiotics are produced alone or in mixture by different groups of micro‐organisms, notably bacteria, fungi and actinomycetes. Some thirty or more antibiotics have now been isolated from each of these groups. Among the bacteria, the spore‐forming aerobes are the most important, although cocci, Gram‐negative and other bacteria have been found to yield important antibiotics, nisin having been isolated from streptococci, and pyocyanase, colicins, and a variety of other compounds from the Gram‐negative rods. Among the fungi, the Penicillium and Aspergillus groups are most important, although the Trichoderma, Chaetomium and other groups, as well as various Basidiomycetes have been found to yield interesting compounds. Among the actinomycetes, the genus Streptomyces is most important, although the genera Nocardia and Micromonospora have also been found to produce interesting antibacterial substances. 4. Out of more than 100 antibiotics that have so far been isolated, only very few have found application as chemotherapeutic agents. These are penicillin, streptomycin and tyrothricin. Among the other more promising antibiotics, one may include bacitracin, subtilin, licheniformin, nisin, aerosporin, polymyxin and Chloromycetin. 5. The introduction of antibiotics as chemotherapeutic agents has revolutionized medical practice. It has pointed a way to the treatment of infections that did not lend themselves previously to therapy. It has given rise to optimistic expectations that new agents will be found that will lend themselves to the treatment of numerous diseases which are still resistant. 6. Among the present‐day problems in the field of antibiotics may be listed the development of resistance among bacteria on prolonged contact with the drug, the search for synergistic agents which would tend to overcome such resistance, a better knowledge of the mode of action of antibiotics, and a search for new antibiotics, notably those that are active upon infections, such as virus and tumour infections, and that do not lend themselves at present to chemotherapy.