Single-Disk Antibiotic-Sensitivity Testing of Staphylococci

With the increasing number of antibiotics available and useful for the treatment of infectious diseases, the development of accurate and simple methods to determine the antibiotic susceptibility of micro-organisms is of increasing importance. The most widely used method at present is the paper-disk sensitivity test. The more cumbersome tube-dilution technique is valuable in special instances in which bactericidal as well as bacteriostatic end-points are needed. Other procedures, such as the plate-dilution, agarwell-diffusion, or ditch-diffusion technique, are more difficult, offer no advantages for routine use, and have been more or less abandoned. In spite of its widespread use there exists considerable variability in the performance of the disk technique, leading to a large number of confusing reports in the literature. There are two methods of performing and interpreting the test. In the first, two or three disks containing different concentrations are used for each antibiotic. The presence or absence of a