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CLSI M100 is the Clinical and Laboratory Standards Institute (CLSI) standard titled Performance Standards for Antimicrobial Susceptibility Testing. It supplies the tables of breakpoints and quality control parameters that laboratories use to interpret susceptibility test results. It is not the test method itself: the 36th edition (M100-Ed36, published January 26, 2026) is valid only when the methods in CLSI M02, M07 and M11 are followed.
Short answer
M100 is the annual interpretation-and-QC companion to CLSI’s testing-method standards. M02 covers disk diffusion, M07 covers dilution testing of aerobic bacteria, and M11 covers dilution testing of anaerobic bacteria. M100 tells a laboratory how to read what those methods produce and which quality control parameters to check.
Definition and scope
According to CLSI’s product page, M100 provides tables for drug selection, interpretation and quality control, built from evidence-based breakpoints and quality control parameters. Those tables cover disk diffusion and dilution testing for aerobic and anaerobic bacteria. CLSI states that the data in the tables are valid only if the methodologies in M02, M07 and M11 are followed.
That sentence is the most useful thing to hold onto when working with the document. A breakpoint from M100 applied to a result generated by a different, non-conforming method is outside what the standard claims to support.
How M100 is used with M02, M07 and M11
The three method standards describe how a test is performed; M100 describes how its output is interpreted. Related guides: the Kirby-Bauer disk diffusion test and broth microdilution for minimum inhibitory concentration cover the method side; this page does not repeat them. Laboratories that summarize results across a facility, for example in an antibiogram, are working from interpretations that follow these tables.
What M100 is and is not
| Question | Where the answer lives | Source |
|---|---|---|
| How is a disk diffusion test performed? | CLSI M02 | CLSI M100 product page |
| How is a dilution test performed for aerobic bacteria? | CLSI M07 | CLSI M100 product page |
| How is a dilution test performed for anaerobic bacteria? | CLSI M11 | CLSI M100 product page |
| How are results interpreted, and which QC parameters apply? | CLSI M100 tables | CLSI M100 product page |
Editions, boldface changes and corrections
M100 is issued as numbered editions. The 36th edition (M100-Ed36) replaces the 35th, published in 2025. CLSI says changes in the tables since the previous edition appear in boldface type. CLSI also notes that the 36th edition has been corrected and publishes a correction notice titled “Corrections for M100-Ed36 (July 2026)” on the product page.
CLSI lists the document in print (ISBN 978-1-68440-305-9, 436 pages) and PDF (ISBN 978-1-68440-306-6, 436 pages) formats, with bundles that pair it with M02 and M07.
Where it matters for labs, clinics and supply decisions
Because M100 sets quality control parameters alongside breakpoints, a new edition affects the working documents of a microbiology bench. The checklist below follows what CLSI and the FDA state about the edition and its recognition.
When a new edition lands: a checklist
- Replace the older M100 tables with the new edition’s tables, rather than mixing editions (CLSI describes the edition as replacing the previous one).
- Scan the boldface text to see what changed since the previous edition.
- Check the correction notice on CLSI’s product page, since the edition may have been corrected after release.
- Confirm that the methods in use still match M02, M07 or M11, because the tables are valid only under those methods.
- For drugs where FDA recognition matters, check the FDA page described below, which lists exceptions and additions.
M100 and FDA recognition
FDA calls susceptibility test interpretive criteria, also known as “breakpoints,” STIC. On its page for FDA-recognized antibacterial susceptibility test interpretive criteria (current as of 06/17/2026), FDA says that unless specific exceptions and additions are identified in its table, it fully recognizes the standards it lists, including CLSI M100, 36th edition (2026). FDA also states that recognition of STIC for a drug does not include recognition of epidemiological cutoff values (ECVs) for that drug. The related FDA-recognized consensus standards entry explains the wider recognition program.
FDA adds that where adequate and well-controlled clinical trials have not established safety and efficacy, the clinical significance of in vitro susceptibility information is unknown.
Common misunderstandings
- “M100 is the test method.” It is not. The methods are in M02, M07 and M11, and the M100 tables are valid only if those are followed.
- “Any edition will do.” Each edition replaces the previous one, and changes are marked in boldface.
- “FDA recognition covers everything in M100.” FDA’s recognition is subject to the exceptions and additions in its table and does not extend to ECVs.
FAQ
Is M100 the method for susceptibility testing?
No. M100 provides interpretive tables and quality control parameters. Disk diffusion is in M02 and dilution testing in M07 (aerobic bacteria) and M11 (anaerobic bacteria).
What is the current edition?
As of 2026-10-29, the current edition is the 36th edition, M100-Ed36, published January 26, 2026. It replaces the 35th edition from 2025.
Does FDA recognize M100?
FDA’s page states that, unless specific exceptions and additions are identified in its table, it fully recognizes the standards listed, including M100 36th edition. Recognition does not include ECVs.
Sources
- CLSI. M100 Performance Standards for Antimicrobial Susceptibility Testing, 36th Edition. https://clsi.org/shop/standards/m100/. Date checked: 2026-10-29.
- U.S. Food and Drug Administration. Antibacterial Susceptibility Test Interpretive Criteria. https://www.fda.gov/drugs/development-resources/antibacterial-susceptibility-test-interpretive-criteria. Page current as of 06/17/2026; date checked: 2026-10-29.
