Overview of changes in the Clinical and Laboratory Standards Institute Performance Standards for Antimicrobial Susceptibility Testing: M100 32nd and 33rd editions

The Clinical and Laboratory Standards Institute Subcommittee on Antimicrobial Susceptibility Testing (AST) publishes annual updates to the M100 Performance Standards for Antimicrobial Susceptibility Testing. This important document contains key information critical to the laboratory’s performance of accurate and current AST. This minireview will highlight and provide supporting data for major changes in the M100 32nd and 33rd editions published in February 2022 and March 2023, respectively. New and revised breakpoints for gram-negative and gram-positive organisms are explained. Proper use of the restructured M100 Table 1 guidance for antimicrobial agents to be considered for testing and reporting is outlined. Reporting guidance for multidrug-resistant gram-negative bacilli is discussed. Other topics within this minireview include additional agents to test and report for direct blood disk diffusion of gram-negative bacilli and quality control range changes and troubleshooting. The minireview concludes with other issues under consideration by the AST Subcommittee.