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How Using CLSI’s M100 Helps the Fight Against Antimicrobial Resistance


In March of this year CLSI will publish the 31st Edition of M100. M100 contains the antibiotic breakpoints that help medical laboratorians throughout the world provide accurate test results to health care providers. These breakpoints aid laboratorians in selecting the most appropriate and effective antimicrobial treatments for patients. Romney M. Humphries, PhD, D(ABMM), member of the Subcommittee on Antimicrobial Susceptibility Testing, the Working Group on AST Testing, and the Working Group on Outreach said, "Antibiotic resistance is an ever-changing clinical dilemma for laboratorians and clinicians alike. We rely on M100 to ensure our lab is best meeting this challenge."

CLSI’s M100 is written by volunteer experts who develop, prescribe, and test antimicrobials, as well as those who report antimicrobial susceptibility test (AST) results. Multiple working groups within the CLSI Antimicrobial Susceptibility Testing Subcommittee address specific aspects of AST, such as determining which antimicrobials to consider for testing and reporting for a specific type of bacterium or assigning breakpoints to newer antimicrobial agents. The AST subcommittee is comprised of experts from health care, industry, and government. These experts include clinical microbiologists, pharmacists, and infectious disease specialists, as well as pharmaceutical and in vitro device manufacturers and statisticians. CLSI volunteers work together to ensure that the most up-to-date and useful information is available in the latest edition of M100.

Antibiotic resistance is one of the biggest public health challenges of our time. Each year in the US alone, at least 2.8 million people get an antibiotic-resistant infection, and more than 35,000 people die.1 Resistance occurs when an organism is no longer treatable by an antimicrobial that was once effective. While an infection can sometimes be treated with another antimicrobial, some organisms are completely resistant to all available treatments. Each new edition of M100 is adapted to reflect changes in treatment recommendations for resistant organisms.

The 31st Edition of M100 is available for preorder now and will be available in several package options with its companions, M02 and M07 when it publishes in March. M100 is also available in a convenient electronic subscription format, M100 Plus.


  1. CDC. Antibiotic/Antimicrobial Resistance. https://www.cdc.gov/drugresistance/index.html. Accessed January 7, 2021.

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