Automated antibiotic susceptibility testing: comparative evaluation of four commercial systems and present state

Automation of AST has come quite some way and is here to stay. In particular, fully automated, "hands off" instruments have great appeal to laboratories with a limited number of well-trained and experienced clinical microbiology personnel. None of the evaluated instruments is perfect, but then neither are the standard or reference techniques. Overnight incubation has been the yardstick since the early days of in vitro AST. Given the usually shorter therapeutic intervals of 4- to 12-hour dosage schedules, it is quite possible that shorter incubation times for in vitro tests will become more of a standard. Until that time, newer, including automatic, techniques need to be evaluated against the more traditional standard methods. Quality control is critical, and since no systematic approach aside from individual manufacturers' suggestions exists, it should be developed by the NCCLS or similar agencies. Quality control might include standards for the evaluation of such equipment and systems because the development of new technology in this area will continue. Overall, reproducibility and accuracy of the instruments and methods evaluated were quite promising and should encourage well-designed studies of clinical correlation and relevance. The AMS equipment has been in use for routine AST in the clinical laboratories of the Seattle Veterans Administration Medical Center and the University of Washington Hospital. Because of its simplicity and flexibility, the Kirby-Bauer method continues to be an alternate technique for certain important clinical isolates, for instance, blood cultures in both laboratories. Finally, it should be remembered that the most critical function of all such equipment is the reliable detection of resistance.