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Global Standards for Antimicrobial Susceptibility Testing

Have Confidence in Your Results With the Latest Edition of M100

CLSI's annual antimicrobial susceptibility testing (AST) supplement, M100, has been updated and is now available. This document represents the most current information for drug selection, antimicrobial susceptibility test interpretation, and quality control. The data provided in M100 are relied upon throughout the world by laboratorians, infectious disease practitioners, and AST device manufacturers.

Ways to Access M100-Ed33

CLSI Subscription Product

M100 Plus

Get full online access to M100, M02, M07, and M11 with added functionality and fast, easy data searching in an electronic format. Plus, you’ll have the added benefit of quick access to related materials via an AST Resource Center.

The Go-To Source for AST Methods and Interpretive Criteria

CLSI has a longstanding reputation for its diligent development of microbiology and antimicrobial susceptibility testing (AST) standards and guidelines on test methods and QC procedures. CLSI annually creates and revises AST breakpoints to meet global public health challenges related to antimicrobial resistance. CLSI is proud to support one health and fighting antimicrobial resistance.

Annual Updates Webinar | Register Now!

Identify the major changes found in the updated edition of CLSI’s M100. Learn to design a strategy for implementing the new 33rd Edition into laboratory practices and get strategies for communicating significant AST and reporting changes to staff.


Moderator: Janet Hindler, MCLS, MT(ASCP), F(AAM)
Speakers: April M. Bobenchik, PhD, D(ABMM), MT(ASCP) Romney M. Humphries, PhD, D(ABMM)


* The webinar will be hosted each day at different times, but the content will be the same.

Read the Latest From the Subcommittee on AST

AST News Update Archives

The CLSI AST Outreach Working Group is part of the CLSI Subcommittee on AST. The working group works to efficiently convey information regarding contemporary AST practices, recommendations, and resources to the clinical microbiology community. They oversee a bi-annual news letter, you can view all past editions on our website—including versions translated into Spanish and Chinese.

Featured CLSI Products | View our products that support preventing antimicrobial resistance.

CLSI Free M100 and M27M44S

Performance Standards for Antimicrobial & Antifungal Susceptibility Testing

Access read-only web versions of M100 and M27M44S for free and quickly reference the most trusted AST and antifungal breakpoints. Available online as a convenient companion to our M100 and M27M44S documents.

CLSI Using M100-Ed32

Using M100: Performance Standards for Antimicrobial Susceptibility Testing

Improve your lab's antimicrobial susceptibility testing (AST) by using this self-paced, online learning program. This interactive program will teach you how to navigate the many tables found in CLSI's document M100.


Breakpoints in Use

CLSI's Outreach Working Group has developed this free, optional spreadsheet that laboratories can use to record breakpoints in use.


Development of In Vitro Susceptibility Testing Criteria and Quality Control Parameters, 5th Edition

This guideline discusses the necessary and recommended data for selecting appropriate breakpoints and quality control ranges for antimicrobial agents.

CLSI Upcoming Live Webinar

What’s New in Susceptibility Testing of Mycobacteria

Date: Thursday, May 4, 2023 | 2:00-3:00 PM Eastern (US) Time

In partnership with CAP.

CLSI On-Demand CLSI and CAP Webinar 2022

Breakpoints Matter: Understanding CLSI Efforts and New CAP Requirements to Ensure Appropriate Antimicrobial Treatment for all Patients

Our Subcommittees: Get Involved

CLSI has subcommittees that are responsible for areas related to AMR. They write draft documents, evaluate and respond to comments on content throughout the document development process, conduct scheduled document reviews, and may be responsible for continual revision of certain documents. Learn more about each below!

Antimicrobial Susceptibility Testing (AST) Subcommittee

The AST Subcommittee provides useful information to laboratories, enabling them to advise clinicians in the selection of appropriate antimicrobial therapy.

Antifungal Susceptibility Testing Subcommittee

The Antifungal Subcommittee collaborates to develop standards and guidelines that promote accurate antifungal susceptibility testing and appropriate reporting.

Veterinary Antimicrobial Susceptibility Testing (VAST)

The VAST Subcommittee collaborates to develop standards and guidelines that promote accurate antimicrobial susceptibility testing and appropriate reporting.