Antibiotic Susceptibility Testing

Abstract

Antimicrobial susceptibility tests are performed in clinical microbiology laboratories to guide physicians in their choice of antimicrobial therapy for a patient with an infection. Susceptibility tests include qualitative methods, like disk diffusion, and a variety of quantitative methods collectively called minimal inhibitory concentration (MIC) methods, many of which are semi- or fully automated. Clinical laboratories typically supplement their disk diffusion or MIC assays with a series of phenotypic tests to increase the sensitivity of detecting borderline or emerging resistance patterns to ultimately enhance the accuracy of the susceptibility test reports. In addition to providing the qualitative results (susceptible, intermediate, or resistant) for each antimicrobial agent tested, laboratories using MIC methods often include the quantitative MIC results (usually reported in μg ml−1) to help guide dosing regimens. Molecular-based tests, such as polymerase chain reaction assays and pyrosequencing strategies, are highly sensitive methods for detecting antimicrobial resistance genes or mutations associated with antimicrobial resistance phenotypes and can provide rapid information on such issues as the presence of MRSA nasal colonization among patients being admitted to a hospital or multidrug-resistant strains of tuberculosis.