CLSI M45, titled "Guidance for Antimicrobial Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria," is a specialized reference manual. It helps clinical microbiologists determine appropriate testing methods, incubation conditions, and interpretive criteria for organisms that are not included in the mainstream CLSI M100 document.

It bridges the gap for organisms that do not grow well on standard media (e.g., Mueller-Hinton agar) or require specific atmospheres (e.g., 5%-10% CO₂).

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Ultimate Guide to CLSI Document M45: Infrequently Isolated or Fastidious Bacteria

The M45 guideline is not a static document. The CLSI is actively working on a , with discussions and data review well underway. Based on meeting minutes, the final draft for the 4th edition was targeted for February 2024 to allow for publication in 2025. Emerging data, such as that for Aerococcus spp., are being used to propose changes to the guideline. The work to define the precise roles of M45 and M100 is also ongoing, with efforts to develop clear definitions for what constitutes an M100 organism versus an M45 organism.

Includes Corynebacterium diphtheriae and opportunistic pathogens like Corynebacterium striatum .

Including Corynebacterium diphtheriae and various non-diphtheria corynebacteria that act as opportunistic pathogens.

Align your internal Standard Operating Procedures (SOPs) with the specific incubation times, temperatures, and media types outlined in the latest M45 edition.

CLSI Document M45, Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria , provides standardized, consensus-based procedures for susceptibility testing of challenging organisms. The third edition supports modern laboratory techniques, such as MALDI-TOF mass spectrometry, and offers essential interpretive criteria for monitoring emerging antimicrobial resistance. For the full standard, visit CLSI .

Report categories (Susceptible, Intermediate, Resistant) to the clinician, noting any intrinsic resistance or testing limitations.

The CLSI M45 document is relevant to:

: Listeria monocytogenes , Corynebacterium species, Bacillus species (excluding B. anthracis ), and Erysipelothrix rhusiopathiae .