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CLSI Publishes a Guideline on Methods for Antimicrobial Susceptibility Testing for Human Mycoplasmas (M43)


Wayne, Pennsylvania, USA—November 2011—The Clinical and Laboratory Standards Institute (CLSI) recently published Methods for Antimicrobial Susceptibility Testing for Human Mycoplasmas; Approved Guideline (M43-A). This document provides guidelines for the performance and quality control of agar and broth microdilution antimicrobial susceptibility tests on human mycoplasmas and ureaplasmas.

“M43-A is the first published method that provides step-by-step procedures for performing agar and broth microdilution testing for human mycoplasmas that also includes and specifies the required quality control procedures and interpretive breakpoints for several antimicrobial agents,” says Ken B. Waites, MD, University of Alabama at Birmingham, Birmingham, Alabama, USA, and chairholder of the committee that developed the document. “The availability of this document will now provide diagnostic laboratories as well as research laboratories in academics, government, and industry a standardized method for testing that should improve reliability of test results and lessen ambiguity and misinformation that can sometimes arise when nonstandard methods are used without rigorously defined quality control procedures, as has been the case for many years in mycoplasmology.”

Antimicrobial susceptibility testing is indicated for any organism that contributes to an infectious process warranting antimicrobial chemotherapy, if its susceptibility cannot be reliably predicted from knowledge of the organism’s identity. Standardized in vitro antimicrobial susceptibility tests are also needed in order to evaluate new antimicrobials against specific groups of organisms in comparison with existing agents. Acquired resistance to one or more classes of antimicrobial agents has emerged in the major mycoplasmal and ureaplasmal species that infect humans, so there is a need to establish accurate and reproducible methods to measure antimicrobial activities in vitro with these organisms. M43-A effectively satisfies this demand.

The document provides guidelines for performance, interpretation, and quality control of in vitro broth microdilution and agar dilution susceptibility tests for several antimicrobial agents suitable for use against Mycoplasma pneumoniae, Mycoplasma hominis, and Ureaplasma species. Information in this document also includes designated reference strains and the expected minimal inhibitory concentration ranges for specific drugs that should be obtained when they are tested.

This guideline is the first publication under the direction of CLSI to describe standardized methods for broth microdilution–and agar dilution–based susceptibility testing of human mycoplasmas and ureaplasmas; the first to designate QC reference strains with defined MIC ranges for various antimicrobial agents; and the first document from any organization to propose interpretive breakpoints for selected antimicrobial agents for use against human mycoplasmas and ureaplasmas. It is intended for use by hospital clinical laboratories; reference microbiology laboratories; and government, industry, and academic research organizations that perform diagnostic testing and/or conduct research in mycoplasmal diseases that affect humans.


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