Abstract
Since the advent of antibiotics as chemotherapeutic agents, the importance of determining the sensitivity to these drugs of micro-organisms present in clinical specimens has become of prime importance. | Prior to Fleming's discovery of penicillin in 1929, and. its subsequent introduction into clinical use in I9I4-I, there was no need for such tests. Since that time, the number of new antibiotics has been rapidly increasing. The introduction of streptomycin, bacitracin, chloramphenicol, aureomycin and terramycin brought about the necessity of choosing among a number of therapeutic agents. It has, therefore, become the work of the laboratory to aid the clinician in making this choice. This the laboratory accomplishes by determining the sensitivity, or the degree of sensitivity, of the infectious agent to the antibiotics in question. | It was soon learned that the bacterial sensitivity to chemotherapeutic agents varies not only from species to species, but also within a species. As certain genera of bacteria have a wide range of reactivity, it has become more important to detect the sensitivity pattern of the infectious agent, rather than to specifically identify the agent. | The methods used in the past have been varied. The tube dilution method is one of the oldest and most reliable. However, due to its lack of simplicity, workers have tried various procedures in an attempt to perfect a more practical method. From a practical point of view, the dried disc method has become the most popular today. | These discs, prepared from a filter or blotter paper, are impregnated with a known concentration of antibiotic and dried. This gives a relatively stable form of the antibiotic, which can be tested in combination with other drugs in a single operation.