Chapter 67 : Susceptibility Test Methods: General Considerations

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Determination of the antimicrobial susceptibilities of significant bacterial isolates is one of the principal functions of the clinical microbiology laboratory. Currently, routine susceptibility testing methods are best standardized for the common aerobic and facultative bacteria and systemic antibacterial agents. The inherent flexibility in drug selection that is provided by the disk diffusion test is an undeniable asset of the susceptibility testing method. There is general agreement that the minimum inhibitory concentration (MICs) is the most basic laboratory measurement of the activity of an antimicrobial agent against an organism. Response rates of at least 80% may be expected for organisms classified as susceptible, although the rates can be lower depending on the site and type of infection. The newest CLSI approach focuses on the rate of interpretive errors near the proposed breakpoint versus rates of errors with MICs more than a single log dilution from the MIC breakpoints. For some key resistances, e.g., carbapenem resistance in Enterobacteriaceae, the most effective confirmatory method is resistance gene detection. Cascade reporting is considered to be an essential part of hospital antimicrobial stewardship programs, as is the production of annual reports that summarize overall susceptibility and resistance patterns (antibiograms).

Citation: Turnidge J, Ferraro M, Jorgensen J. 2011. Susceptibility Test Methods: General Considerations, p 1115-1121. In Versalovic J, Carroll K, Funke G, Jorgensen J, Landry M, Warnock D (ed), Manual of Clinical Microbiology, 10th Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816728.ch67
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Comparison of zone diameters with MICs of a hypothetical antimicrobial agent.

Citation: Turnidge J, Ferraro M, Jorgensen J. 2011. Susceptibility Test Methods: General Considerations, p 1115-1121. In Versalovic J, Carroll K, Funke G, Jorgensen J, Landry M, Warnock D (ed), Manual of Clinical Microbiology, 10th Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816728.ch67
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