Role of the microbiology laboratory in monitoring and identifying resistance: Use of molecular biology

Antimicrobial resistance is an increasing problem in the United States. Early detection of emerging trends in antimicrobial resistance may facilitate implementation of effective control measures. Most antimicrobial susceptibility testing is qualitative, in that it categorizes isolates as susceptible, intermediate, or resistant. This approach is relatively inexpensive and generally adequate for clinical purposes. Qualitative susceptibility testing has some limitations for monitoring for emerging resistance. Selective quantitative susceptibility testing may be useful in detecting early trends toward elevated minimal inhibitory concentrations. Molecular methods have a role also in characterizing mechanisms of resistance and in the typing of resistant strains to determine patterns of spread. Laboratory monitoring of emerging resistance must be associated with an effective infection control policy and a willingness to modify practice in a rational manner based upon the trends detected.