CLSI M45 is an indispensable companion to routine susceptibility testing. It offers a standardized safety net for challenging organisms that commercial panels ignore. While not every lab will run M45 daily, every clinical microbiology lab should have access to it – either internally or via a reference lab – and understand its principles to ensure appropriate antibiotic therapy for patients with uncommon or fastidious infections.
Always refer to the original CLSI M45 document (current edition) for official breakpoints, QC tables, and procedural details. This article is for educational use and does not replace the copyrighted standard.
This guide outlines the purpose, content, and application of the CLSI M45 document
, titled "Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria." Current Edition:
The 3rd Edition (M45-Ed3) was published in 2016, with ongoing updates, including emerging data on Pseudomonas species other than P. aeruginosa (POPA) planned for a 4th edition.
To provide clinical microbiology labs with standardized, actionable methods for susceptibility testing of fastidious or rare bacteria not covered in broader CLSI standards like M02, M07, or M100. Availability: The PDF document is available for purchase on the 1. Scope of the CLSI M45 Guideline
The M45 document focuses on organisms that are either difficult to grow (fastidious) or infrequently encountered in clinical settings but can cause serious infections. Clinical & Laboratory Standards Institute | CLSI Key Bacteria Covered: Corynebacterium B. anthracis Lactobacillus Leuconostoc Pediococcus Aerococcus Granulicatella spp., and various fastidious aerobic bacteria. When to Use:
Use this document when an organism is identified, but susceptibility cannot be reliably predicted, and standard M100 methods do not apply. Exclusions:
It does not address commercial susceptibility testing devices, which often have their own FDA-cleared, specific protocols. Clinical & Laboratory Standards Institute | CLSI 2. Core Methodologies in M45
The guideline details standardized methods to ensure consistent results: Broth Microdilution:
Recommends the broth microdilution method for testing fastidious and uncommon bacteria. Agar Disk Diffusion:
Provides standardized procedures for interpreting disk susceptibility for specific organisms. Quality Control (QC):
Lists specific QC bacteria to ensure testing accuracy, with QC ranges provided in the document's tables. ResearchGate 3. Key Components of the Document Organism-Specific Tables: clsi document m45 pdf
Each section/table gives recommendations for antimicrobial agents to test, MIC interpretive criteria, and disk diffusion zone diameter breakpoints. Updated Taxonomy:
The document includes updates for bacteria often identified using modern technologies like MALDI-TOF mass spectrometry or gene sequencing. Clinical Relevance:
Provides guidance on when to actually perform testing, recognizing that some, but not all, of these organisms require routine testing for resistance. Clinical & Laboratory Standards Institute | CLSI 4. M45 vs. Other CLSI Guidelines CLSI M100:
Performance standards for commonly encountered bacteria (e.g., Enterobacterales Specialized standards for organisms not addressed in M100.
If an organism is covered in M100, that standard takes precedence over M45. ResearchGate 5. Best Practices for Implementing M45 Always Use the Current Version:
Replace old editions with the newest version to ensure accurate resistance detection. Integrate with WHONET: Use software like WHONET 5.6
to input the specific M45 interpretive criteria for disk diffusion, particularly if not using standard M100 breakpoints. Validation:
Laboratory staff should review the "notes" section in the tables, as they often contain critical information regarding specific organism-drug pairings. www.nih.org.pk
Disclaimer: This guide is a summary. Always refer to the actual, purchased CLSI M45 PDF document for the most current, comprehensive, and legally validated standards.
The CLSI M45 document, currently in its 3rd edition, provides essential standardized testing methods and interpretive criteria for antimicrobial susceptibility testing of fastidious or infrequently isolated bacteria Clinical & Laboratory Standards Institute | CLSI
. It offers specialized protocols for 14 organism groups, including Listeria monocytogenes , filling gaps left by more general guidelines Clinical & Laboratory Standards Institute | CLSI . For more details, visit
The CLSI M45 document, titled "Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria," provides critical guidelines for testing organisms that fall outside the more common species covered in the CLSI M100 standard. Key Features of CLSI M45 CLSI M45 is an indispensable companion to routine
Standardized Methodology: It describes broth microdilution and agar disk diffusion methods specifically tailored for fastidious or rare bacteria.
Target Organisms: Provides testing conditions and interpretive criteria for organisms like Corynebacterium spp., Abiotrophia spp., Granulicatella spp., and Bacillus spp. (excluding B. anthracis).
Bioterrorism Preparedness: Includes specialized procedures for public health laboratories to handle potential bacterial agents of bioterrorism.
Advanced Identification Support: The latest editions include tables and taxonomic updates for organisms identified via MALDI-TOF mass spectrometry or sequencing.
Interpretive Criteria: Offers Minimal Inhibitory Concentration (MIC) and disk diffusion (DD) breakpoints that help clinicians select therapy for unusual pathogens. Access and Formats
The document is available for purchase and download through the following platforms:
The CLSI (Clinical and Laboratory Standards Institute) document M45 is a guideline for antimicrobial susceptibility testing (AST) of fungi. Here's some useful content related to the CLSI document M45 PDF:
What is CLSI M45?
CLSI M45 is a document that provides guidelines for the performance and interpretation of antimicrobial susceptibility testing (AST) of fungi, including yeast and molds. The document is intended for clinical microbiologists, laboratory professionals, and healthcare providers.
Content of CLSI M45
The CLSI M45 document covers the following topics:
Key Points from CLSI M45
Some key points from the CLSI M45 document include:
How to Access CLSI M45 PDF
The CLSI M45 document is available for purchase on the CLSI website (www.clsi.org). The document can be downloaded as a PDF file.
Relevance of CLSI M45
The CLSI M45 document is relevant to:
By following the guidelines outlined in CLSI M45, laboratories can ensure accurate and reliable AST results, which are essential for guiding effective antifungal therapy and improving patient outcomes.
CLSI Document M45 (3rd Edition) provides standardized methods for antimicrobial dilution and disk susceptibility testing of infrequent or fastidious bacteria, covering organisms like Abiotrophia, Vibrio spp., and bioterrorism agents. It establishes essential breakpoints and QC ranges, offering detailed technical procedures for broth microdilution and agar disk diffusion to ensure accurate lab results. For the complete document guidelines, visit CLSI Webstore. preview_CLSI+M45-Ed3.pdf - ANSI Webstore
Many hospitals, university libraries, and reference labs subscribe to the CLSI eSubscription Service. This provides unlimited access to all current CLSI documents, including M45, via a portal. Users can download PDFs for internal use.
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There are three legitimate ways to get the official M45 Ed.4 document in PDF format:
Pro tip: Academic institutions and low-income countries may qualify for reduced pricing or free access via the CLSI Global Health Partnerships.
Scenario: A blood culture grows Granulicatella adiacens (nutritionally variant streptococcus) in a patient with endocarditis. Your automated system gives "no interpretative data." Always refer to the original CLSI M45 document
Using the CLSI M45 PDF:
Without the M45 PDF, this patient might be misreported and undertreated.