J Clin Microbiol. 2021 Sep 22:JCM0021321. doi: 10.1128/JCM.00213-21. Online ahead of print.
The Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing (AST) develops and publishes standards and guidelines for AST methods and results interpretation, in an annual update to the Performance Standards for Antimicrobial Susceptibility Testing (M100). This mini-review will discuss changes to M100 for the 31st Edition, including new and revised breakpoints and testing recommendations. New MIC and disk diffusion breakpoints are described for azithromycin (Shigella spp.), imipenem-relebactam (Enterobacterales, Pseudomonas aeruginosa and anaerobes), lefamulin (Staphylococcus aureus, Haemophilus influenzae and Streptococcus pneumoniae) and disk breakpoints for azithromycin and Neisseria gonorrhoeae. The rationale behind revised oxacillin MIC breakpoints for select staphylococci is discussed. Updates to test methods include a method for disk diffusion using positive blood culture broth and use of linezolid to predict tedizolid susceptibility. Clarification on which drugs to suppress on bacteria isolated from the cerebrospinal fluid, and clarification on the use of a caret symbol attached to the intermediate category ("I^") to indicate those antimicrobials that concentrate in the urine.