CLSI M100 31st Edition: New Breakpoints, Disk Diffusion from Blood Cultures, and Revised Oxacillin Thresholds
This overview summarizes key changes in the 31st edition of the CLSI Performance Standards for Antimicrobial Susceptibility Testing (M100), including new MIC and disk diffusion breakpoints for imipenem-relebactam, lefamulin, and azithromycin across multiple organism groups. Notable methodological updates include disk diffusion testing directly from positive blood culture broth and use of linezolid to predict tedizolid susceptibility. Revised oxacillin MIC breakpoints for select staphylococci and clarifications on CSF isolate reporting reflect the ongoing refinement of interpretive criteria.
The original study
Overview of Changes to the Clinical and Laboratory Standards Institute
- Authors
- Humphries R, Bobenchik AM, Hindler JA, Schuetz AN
- Journal
- Journal of clinical microbiology
- Type
- Journal Article, Review
- PMID
- 34550809
Original abstract
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 minireview 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), and lefamulin (Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pneumoniae), and disk breakpoints are described 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. There is 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.