Chapter 70 : Susceptibility Test Methods: General Considerations

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The main objective of susceptibility testing is to predict the outcome of treatment with the antimicrobial agents tested. The test results are generally reported to the treating physician, using the categories of susceptible, intermediate, and resistant. From the laboratory perspective, the key decisions involve the selection of a susceptibility testing method and the antimicrobial agents to be tested for each specimen and pathogen type. The principal methods used internationally are those of the Clinical and Laboratory Standards Institute (CLSI), based in the United States, and the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Both organizations have a sophisticated approach to the setting of breakpoints (interpretive criteria) which permit the categorization of the susceptibility test results. This approach includes the collation and analysis of MIC distribution data, pharmacokinetic and pharmacodynamic data and associated target values, and clinical and bacteriological response rates from prospective clinical trials. This analysis is followed by the correlation of MICs and zone diameter distributions in order to establish breakpoints for commonly used methods. Modern susceptibility testing methods are often supplemented by specialized phenotypic and/or molecular testing to ensure that critical resistances and resistance mechanisms are detected.

Citation: Turnidge J. 2015. Susceptibility Test Methods: General Considerations, p 1246-1252. In Jorgensen J, Pfaller M, Carroll K, Funke G, Landry M, Richter S, Warnock D (ed), Manual of Clinical Microbiology, Eleventh Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817381.ch70
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Comparison of zone diameters with MICs of a hypothetical antimicrobial agent. doi:10.1128/9781555817381.ch70.f1

Citation: Turnidge J. 2015. Susceptibility Test Methods: General Considerations, p 1246-1252. In Jorgensen J, Pfaller M, Carroll K, Funke G, Landry M, Richter S, Warnock D (ed), Manual of Clinical Microbiology, Eleventh Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817381.ch70
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