This standard provides reference methods for determining minimal inhibitory concentrations of anaerobic bacteria by agar dilution and broth microdilution.

Clinical and Laboratory Standards Institute standard M11 - Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria describes the reference standard agar dilution method (Wadsworth) and the alternative broth microdilution method.

Antimicrobial resistance patterns for many anaerobic bacteria have changed significantly over the past several years, resulting in a lack of predictability for many species. Susceptibility testing of anaerobes is recommended for surveillance purposes and for specific clinical situations. The agar dilution method is well suited for surveillance testing and research. It is also the standard with which other methods are compared.

The alternative method, broth microdilution, is well suited for the medical laboratory but is currently limited to testing Bacteroides spp. and Parabacteroides spp. organisms and selected antimicrobial agents. QC criteria for each procedure are also described.

This standardized procedure, when used in conjunction with the M100 tables, includes the most current information for drug selection, interpretation, QC, and antibiogram reports. When new problems are recognized or improvements in these criteria are made, changes will be incorporated into future editions of this standard and in M100.