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M100-S27 Revised AST Breakpoints Document


Wayne, Pennsylvania, USA —To improve detection and reporting of antimicrobial resistance, the Clinical and Laboratory Standards Institute (CLSI) has published a revised edition of its annual supplement providing revised breakpoints, new testing recommendations, and reporting changes needed to incorporate into routine practice.

The document, titled Performance Standards for Antimicrobial Susceptibility Testing (M100, 27th ed.), provides updated tables for the CLSI antimicrobial susceptibility testing (AST) standards Performance Standards for Antimicrobial Disk Susceptibility Tests (M02-Ed12), Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically (M07-Ed10), and Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria (M11-Ed8). Clinicians rely on information from the microbiology laboratory to treat their patients. Due to the importance of AST results, these tests need to be performed under optimal conditions and laboratories must be capable of providing results for the newest antimicrobial agents. Using procedures standardized in M02, M07, and M11, M100 includes the essential data for drug selection, interpretation, and QC needed for clinical practice.

“The most recent edition of M100 includes multiple updates that clarify AST recommendations, but three new recommendations are really critical for detecting resistance in two of the Centers for Disease Control and Prevention’s urgent antibiotic resistance threats: carbapenemase-producing Enterobacteriaceae and drug-resistant Neisseria gonorrhoeae,” states Dr. Jean B. Patel, PhD, D(ABMM), Centers for Disease Control and Prevention, Atlanta, Georgia, USA and Chairholder of the Subcommittee on Antimicrobial Susceptibility Testing,. “Specifically, the following information was added:

  • A colistin epidemiological cutoff value (ECV) for species of Enterobacteriaceae. This will help laboratories identify new types of colistin resistance, such as the plasmid-mediated mcr-1 mechanism. Early recognition improves the ability to prevent infections that may be nearly impossible to treat.
  • A carbapenemase detection test called the modified carbapenem inactivation method (mCIM), which has improved sensitivity for detecting OXA-type carbapenemases compared to other tests, without sacrificing specificity. Laboratories need a reliable carbapenemase detection test to identify when enhanced infection control measures may be needed to prevent the spread of resistant infections. The mCIM is easy to perform and inexpensive.
  • An azithromycin ECV for N. gonorrhoeae. This value allows for detection of azithromycin resistance mechanisms and, in turn, continual development of effective treatment recommendations. Fast and effective treatment is the best way to stop an infection from spreading.”

Major changes to this edition of M100 include the following:

  • Results reporting definitions were revised to harmonize with the CLSI library of susceptibility testing documents.
  • Colistin minimal inhibitory concentration breakpoints were revised for Pseudomonas aeruginosa.
  • Telavancin disk diffusion breakpoints were deleted from multiple tables.
  • ECVs were added for azithromycin and N. gonorrhoeae.
  • ECVs were added for colistin and Enterobacter aerogenes, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and Raoultella ornithinolytica.
  • The mCIM was added for suspected carbapenemase production in Enterobacteriaceae.

QC ranges were added and/or changed for the following drugs and organisms:

  • Cefepime (P. aeruginosa)
  • Cefepime-tazobactam (1:1) (E. coli, Staphylococcus aureus, P. aeruginosa, K. pneumoniae)
  • Gepotidacin (N. gonorrhoeae)
  • Meropenem (E. coli, P. aeruginosa)
  • Meropenem-vaborbactam (E. coli, S. aureus, P. aeruginosa, K. pneumoniae)
  • Nafithromycin (S. aureus, Haemophilus influenzae, Streptococcus pneumoniae, Enterococcus faecalis)
  • Pexiganan (S. aureus, E. faecalis, E. coli, P. aeruginosa, H. influenzae, S. pneumoniae)
  • Tedizolid (S. aureus)

For more information about M100, contact Patrick McGinn at pmcginn@clsi.org or +1.484.588.5933.

CLSI sets the standard for quality in medical laboratory testing. A not-for-profit membership organization, CLSI brings together the global laboratory community for the advancement of a common cause: to foster excellence in laboratory medicine.

For nearly 50 years, our members, volunteers, and customers have made CLSI a respected, transformative leader in the development and implementation of medical laboratory testing standards. Through our unified efforts, we will continue to set and uphold the standards that drive quality test results, enhance patient care delivery, and improve health care around the world.

By using CLSI standards, laboratorians can improve process quality, speed the development of standard operating procedures, and implement safer practices with greater ease and efficiency.

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