Instrumentation in antimicrobial susceptibility testing

Studies in the 1960s demonstrated the problems of variability in susceptibi lity testing methods, especially those affecting the performance of disc di ffusion procedures. These studies made apparent the need for standardizatio n and resulted in more clearly defined performance limits for growth medium , incubation conditions, inoculum concentration, disc content for diffusion methods, the setting of interpretative MIC breakpoints and the establishme nt of quality control parameters. More recently, there has been a growing i nterest in the use of instrumentation for reading disc diffusion tests and the endpoints of agar or broth dilution MIC determinations. Instrumentation ranges in complexity from the simple optical reading of zones of inhibitio n or growth endpoints, requiring operator interpretation, to more sophistic ated devices for reading, recording and 'expert system' analysis of results with interfacing of instruments to laboratory information management syste ms. Some of the more developed systems are fully automated and can also ide ntify the organisms tested. The pressure to reduce labour costs and provide results earlier favours the use of more automated systems whilst the requi rement for resistance surveillance provides impetus for the use of systems that provide quantitative results and electronic data handling.