Improving antimicrobial susceptibility testing

Acceptable susceptibility methodology is changing because of such factors as increasing bacterial-resistance to antimicrobial agents and refinement of previous susceptibility testing methods. National Committee for Clinical Laboratory Standards' guidelines, therefore, must be observed at all times. Information from a table for a specified organism cannot be extrapolated for use with another organism. Only susceptibilities for antimicrobial agents recommended by the National Committee for Clinical Laboratory Standards should be reported routinely. If laboratory personnel digress from recommended methodology, an inaccurate susceptibility pattern may result. We describe frequent misconceptions in susceptibility testing, summarize the current recommendations for in vitro susceptibility testing for commonly isolated pathogens, and identify the appropriate antimicrobial agents to be tested.