Antimicrobial susceptibility testing of anaerobic bacteria: review and update on the role of the National Committee for Clinical Laboratory Standards.

The National Committee for Clinical Laboratory Standards (NCCLS) has published a standard method (M11-A) and alternative methods (M17-P) for susceptibility testing of anaerobic bacteria. (These will be combined in the next edition of M11.) Even though M11-A describes the "standard reference" method, there is not agreement as to which method, if any, is the "best" method. In recent years NCCLS subcommittee members have realized that results obtained by microdilution or disk elution may vary markedly from those obtained with the reference agar dilution method. Furthermore, they have recognized the difficulty of relating in vitro susceptibility results to clinical success or failure. In response to these problems, the NCCLS convened a working group to consider recommendations about susceptibility testing. This group has concluded that for most individual patients a susceptibility test may not be required but that present methods can be useful for comparisons of the activity of various drugs and for surveillance of resistance patterns.