Dear Stanley: 2018 CLSI M100 Updates

Dear Stanley,

CLSI M100 was updated this year. What are some of the biggest changes and how do they impact QC in my lab?

Ruth from Chicago, IL

Dear Ruth,

Great question!

In 2018, there were many changes to CLSI M100 (Performance Standards for Antimicrobial Susceptibility Testing), M02 (Performance Standards for Antimicrobial Disk Susceptibility Test), and M07 (Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically) that impact quality control in clinical laboratories. Here are five significant updates you should be aware of:

1. Revised nomenclature:

  • Propionibacterium acnes updated to Cutibacterium acnes (LPSN)
  • Clostridium difficile updated to Clostridioides difficile (LPSN)
  • Enterobacter aerogenes updated to Klebsiella aerogenes (LPSN)
  • Fusobacterium nucleatum to Fusobacterium
  • Β-lactam/ Β-lactamase inhibitor combinations now referred to as Β-lactam combination agents

2. Modified Hodge Test: All references to this test were deleted because the test was suboptimal and had poor specificity and sensitivity.

3. Special QC procedures for β-Lactam combination agents and new QC tables for β-Lactam combination agents added:

  • β-Lactamase producing QC strains were removed from routine QC tables. These strains have been put in their own tables for QC of single antibiotics: 4A-1 (Disk Diffusion) and 5A-1 (MIC).
  • New QC ranges for specific β-Lactam combination agents are now found in tables 4A-2 (Disk Diffusion) and 5A-2 (MIC).
  • For β-Lactam combination agents, you are now required to confirm the integrity of the QC strain before use by testing the respective single antibiotic listed in orange for the respective combination agent (see note C under table 4A-2). For example, when testing Escherichia coli ATCC® 35218™ against Piperacillin-tazobactam discs, you must first test a piperacillin disc with the QC strain and ensure it produces a correct zone of inhibition or MIC before testing with the β-Lactam combination agent. If zone size is acceptable, you can proceed with using ATCC® 35218™ for QC of the piperacillin-tazobactam discs.

4. Updates to Maintenance of QC Strains procedure (M02 and M07): Information about converting from daily to weekly QC (M07) was deleted.

5. Added new QC strains and QC ranges for Escherichia coli NCTC 13353, Klebsiella pneumoniae ATCC® BAA-2814™, and Acinetobacter baumanii NCTC 13304

You can find all these changes and more listed in the Overview of Changes in the applicable CLSI standards.

Visit our website to find the QC strains your lab needs to meet CLSI standards. Our Technical Support team is here to help if you need guidance finding the right strain and format for your lab.


Stanley Staphylococcus


Stanley Staphylococcus is a Master Micro-Technologist at Microbiologics, where he is responsible for helping customers understand why microorganisms behave the way they do. You could say he’s somewhat of a psychologist. Microbiologics has been lucky to have Stanley, a graduate of Gram-Positive Cocci University, as a member of their renowned Technical Support Team for over 20 years. Stanley says his favorite type of people are microbiologists and he enjoys traveling far and wide to meet them. Amazingly, Stanley has been on every continent – even Antarctica!

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  1. Elena

    I can’t find a reference link to CLSI website confirming that they now recognize revised nomenclature mentioned above.
    Could you provide it?

    1. mmMicrobiologics

      Elena – The nomenclature changes are addressed in the M100 Standard in the “Overview of Changes Section.” If you do not already have the current revision of M100, you can view the changes by accessing the free version online by following this link:

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