Antimicrobial susceptibility testing: a critical evaluation.

Antibiotic susceptibility test results must be interpreted cautiously. There are important differences between the laboratory and natural environments. There are also important differences between disc and dilution tests, and between laboratories. Laboratory tests can demonstrate antagonism and synergy. Because beta-lactamases can be induced, beta-lactam susceptibility may have to be monitored during therapy. Increases in the incidence of drug resistance are particularly important in nosocomial infections.