Skip to main content
  • ASM
    • Antimicrobial Agents and Chemotherapy
    • Applied and Environmental Microbiology
    • Clinical Microbiology Reviews
    • Clinical and Vaccine Immunology
    • EcoSal Plus
    • Eukaryotic Cell
    • Infection and Immunity
    • Journal of Bacteriology
    • Journal of Clinical Microbiology
    • Journal of Microbiology & Biology Education
    • Journal of Virology
    • mBio
    • Microbiology and Molecular Biology Reviews
    • Microbiology Resource Announcements
    • Microbiology Spectrum
    • Molecular and Cellular Biology
    • mSphere
    • mSystems
  • Log in
  • My alerts
  • My Cart

Main menu

  • Home
  • Articles
    • Current Issue
    • Accepted Manuscripts
    • COVID-19 Special Collection
    • Archive
    • Minireviews
  • For Authors
    • Submit a Manuscript
    • Scope
    • Editorial Policy
    • Submission, Review, & Publication Processes
    • Organization and Format
    • Errata, Author Corrections, Retractions
    • Illustrations and Tables
    • Nomenclature
    • Abbreviations and Conventions
    • Publication Fees
    • Ethics Resources and Policies
  • About the Journal
    • About JCM
    • Editor in Chief
    • Editorial Board
    • For Reviewers
    • For the Media
    • For Librarians
    • For Advertisers
    • Alerts
    • RSS
    • FAQ
  • Subscribe
    • Members
    • Institutions
  • ASM
    • Antimicrobial Agents and Chemotherapy
    • Applied and Environmental Microbiology
    • Clinical Microbiology Reviews
    • Clinical and Vaccine Immunology
    • EcoSal Plus
    • Eukaryotic Cell
    • Infection and Immunity
    • Journal of Bacteriology
    • Journal of Clinical Microbiology
    • Journal of Microbiology & Biology Education
    • Journal of Virology
    • mBio
    • Microbiology and Molecular Biology Reviews
    • Microbiology Resource Announcements
    • Microbiology Spectrum
    • Molecular and Cellular Biology
    • mSphere
    • mSystems

User menu

  • Log in
  • My alerts
  • My Cart

Search

  • Advanced search
Journal of Clinical Microbiology
publisher-logosite-logo

Advanced Search

  • Home
  • Articles
    • Current Issue
    • Accepted Manuscripts
    • COVID-19 Special Collection
    • Archive
    • Minireviews
  • For Authors
    • Submit a Manuscript
    • Scope
    • Editorial Policy
    • Submission, Review, & Publication Processes
    • Organization and Format
    • Errata, Author Corrections, Retractions
    • Illustrations and Tables
    • Nomenclature
    • Abbreviations and Conventions
    • Publication Fees
    • Ethics Resources and Policies
  • About the Journal
    • About JCM
    • Editor in Chief
    • Editorial Board
    • For Reviewers
    • For the Media
    • For Librarians
    • For Advertisers
    • Alerts
    • RSS
    • FAQ
  • Subscribe
    • Members
    • Institutions
Letter to the Editor

Susceptibility Categories Should Be Agreed Upon

Ernst Molitor
Carey-Ann D. Burnham, Editor
Ernst Molitor
aInstitute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Carey-Ann D. Burnham
Washington University School of Medicine
Roles: Editor
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
DOI: 10.1128/JCM.00620-19
  • Article
  • Figures & Data
  • Info & Metrics
  • PDF
Loading

LETTER

I thank the editor in chief very much for his comic strip beautifully describing the differences and similarities in susceptibility (“S”) categories as defined by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) (1). Judging from my experience as a clinical microbiologist, antimicrobials assigned to the intermediate susceptibility (“I”) category in antibiograms reported according to CLSI or former EUCAST rules are hardly ever used. Resistance (“R”) to antimicrobial agents is growing relentlessly; concomitantly, the number of cases in which clinicians, facing limited treatment options, have to consider antimicrobials categorized as “I” increases. Antimicrobials must be used based on the best available evidence, balancing the needs of the individual patients and the selective pressure caused; concise, clear, and unambiguous communication of laboratory results to clinicians is of paramount importance. Therefore, I very much applaud the decision of the EUCAST steering committee to change the definition of “I” so as to remove the uncertainty this category has been tainted with historically (2). Under current EUCAST rules, results which are fraught with substantial uncertainty are tagged with a warning message (“Area of Technical Uncertainty” [ATU]), which must be dealt with by the laboratory. For results marked as ATU, an alternative test may be used, or the susceptibility categories that apply may be flagged as uncertain, suppressed from reporting, or stepped up (i.e., the marked result may be reported as resistant). Disadvantageously, EUCAST still has failed to change the susceptibility categories for yeasts. Hopefully, this inconsistency, which could cause substantial confusion, will be remedied soon. The principle of sticking to the traditional S, I, and R shorthand symbols and yet changing the definitions of the susceptibility categories comes at a price: intense and ongoing education is urgently needed to avoid misunderstandings and misinterpretations.

Sadly, despite impressive efforts, CLSI and EUCAST have not yet unified their rules for reporting qualitative susceptibility results. The CLSI committee on antimicrobial susceptibility testing has discussed the matter extensively (see p. 21 to 24 in reference 3) and came to conclusions different from EUCAST’s.

EUCAST’s new definition of the category “I” (“susceptible, increased exposure”) is quite similar to CLSI’s definition of “Susceptible Dose Dependent” (SDD) (see p. 242 in reference 4). For bacteria, CLSI introduced this susceptibility category in 2014 (see p. 18 in reference 5); at that time, EUCAST did not adopt the change. In CLSI M100, SDD is used increasingly, but still rarely, even in the current edition (4): SDD is listed only for cefepime in Enterobacteriaceae (Enterobacterales), ceftaroline in Staphylococcus aureus, and daptomycin in Enterococcus faecium (see p. 35, 63, and 70 in reference 4). For Pseudomonas aeruginosa, for instance, most antimicrobial agents effective in strains with wild-type susceptibility depend on application of high dosages for their efficacy, with meropenem the most notable exception to this rule. The current CLSI documents include comments to convey this need. For P. aeruginosa, as well as for many other bacterial species where using this category would be prudent, SDD is not used in the CLSI standard (see p. 42 to 45 in reference 4). In my view, it would be advantageous to use SDD or “I” as defined by EUCAST instead of adding lengthy comments that might not always enjoy the attention of the clinicians to whom the results are being reported. The recipients’ attention to the change must be caught by proper legends to the antibiogram, a link to the dosage table used for determination of the breakpoints, and continuing education. General use of “I” to convey the need for a high exposure of the microbes to the antimicrobial in question where appropriate is expected to be agreed upon by EUCAST in 2020 and may be used beforehand, which our laboratory chose to do. Creating new susceptibility categories might attract the recipients’ attention for the change in definitions to be noted. Susceptibility categories that are rarely used, however, will not spread the news effectively and may be misunderstood. CLSI and EUCAST will have to fulfill the need for education about both the new terminology and changes in the definition of existing terms.

To make sure the recipients of our susceptibility reports note the changes that the definitions of the categories “S” and “I” have been subjected to by EUCAST (6), we introduced the following colors on our reports: susceptible and resistant assignments have been printed with a white “S” or “I” on a green background and a white “R” on a red background, respectively, since 1 January 2019 (anonymized examples of our reports are available as supplemental material). Until EUCAST extends the new definition of the category “I” to yeasts, our laboratory will continue to display a black “I” on an orange background to indicate “intermediate” results. The definitions of the white “I” on a green background and the black “I” on an orange background are included in the legends of antibiograms which contain these shorthand symbols. Admittedly, the colors our laboratory has chosen suffer from the major disadvantage of being hard to discern by persons stricken with color blindness; the advantages of the analogy to traffic lights, however, in our opinion, overruled this concern. With our laboratory information software (LIS), based on open source software, the changes to our reports were achieved quickly and easily and at no cost.

EUCAST decided to stick with a mere three categories for reporting susceptibility results to clinicians and to change the definition of “I” in a way that removes the ambiguities previously included in this category. While CLSI has introduced the SDD category, in my opinion, they still use this category very restrictively. In addition, as Albert Einstein has pointed out, “everything should be as simple as it can be, but not simpler.” Three susceptibility categories, wisely defined, are completely sufficient and allow for lengthy comments on laboratory reports to be restricted to cases where they are both useful and unavoidable. In my humble opinion, the guidelines should be unified with regard to the categories susceptibility results are assigned to; three unambiguous, clear-cut categories offer comprehensive and yet detailed categorical reporting of susceptibility results.

FOOTNOTES

  • Supplemental material for this article may be found at https://doi.org/10.1128/JCM.00620-19.

  • For the author reply, see https://doi.org/10.1128/JCM.00919-19.

  • Copyright © 2019 American Society for Microbiology.

All Rights Reserved.

REFERENCES

  1. 1.↵
    1. McAdam AJ
    . 2019. The divergent meanings of “I” for the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing: a micro-comic strip. J Clin Microbiol 57:e00050-19. doi:10.1128/JCM.00050-19.
    OpenUrlFREE Full Text
  2. 2.↵
    EUCAST. 2019. Clinical breakpoints and dosing of antibiotics. http://www.EUCAST.org/clinical_breakpoints/.
  3. 3.↵
    1. Hackenbrack ML
    . 2019. Subcommittee on Antimicrobial Susceptibility Testing: minutes of the meeting 3–5 June 2018. https://CLSI.org/media/3013/2018_june_ast_agenda_summary_minutes_approved.pdf.
  4. 4.↵
    Clinical and Laboratory Standards Institute. 2019. Performance standards for antimicrobial susceptibility testing. 29th ed. CLSI document M100. Clinical and Laboratory Standards Institute, Wayne, PA.
  5. 5.↵
    Clinical and Laboratory Standards Institute. 2014. Performance standards for antimicrobial susceptibility testing. 24th ed. CLSI document M100. Clinical and Laboratory Standards Institute, Wayne, PA.
  6. 6.↵
    EUCAST. 2019. New definitions of S, I and R. http://www.EUCAST.org/newsiandr/.
PreviousNext
Back to top
Download PDF
Citation Tools
Susceptibility Categories Should Be Agreed Upon
Ernst Molitor
Journal of Clinical Microbiology Aug 2019, 57 (9) e00620-19; DOI: 10.1128/JCM.00620-19

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Print

Alerts
Sign In to Email Alerts with your Email Address
Email

Thank you for sharing this Journal of Clinical Microbiology article.

NOTE: We request your email address only to inform the recipient that it was you who recommended this article, and that it is not junk mail. We do not retain these email addresses.

Enter multiple addresses on separate lines or separate them with commas.
Susceptibility Categories Should Be Agreed Upon
(Your Name) has forwarded a page to you from Journal of Clinical Microbiology
(Your Name) thought you would be interested in this article in Journal of Clinical Microbiology.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Share
Susceptibility Categories Should Be Agreed Upon
Ernst Molitor
Journal of Clinical Microbiology Aug 2019, 57 (9) e00620-19; DOI: 10.1128/JCM.00620-19
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo
  • Top
  • Article
    • LETTER
    • FOOTNOTES
    • REFERENCES
  • Figures & Data
  • Info & Metrics
  • PDF

KEYWORDS

antibacterial susceptibility testing
CLSI
EUCAST
susceptibility category

Related Articles

Cited By...

About

  • About JCM
  • Editor in Chief
  • Board of Editors
  • Editor Conflicts of Interest
  • For Reviewers
  • For the Media
  • For Librarians
  • For Advertisers
  • Alerts
  • RSS
  • FAQ
  • Permissions
  • Journal Announcements

Authors

  • ASM Author Center
  • Submit a Manuscript
  • Article Types
  • Resources for Clinical Microbiologists
  • Ethics
  • Contact Us

Follow #JClinMicro

@ASMicrobiology

       

ASM Journals

ASM journals are the most prominent publications in the field, delivering up-to-date and authoritative coverage of both basic and clinical microbiology.

About ASM | Contact Us | Press Room

 

ASM is a member of

Scientific Society Publisher Alliance

 

American Society for Microbiology
1752 N St. NW
Washington, DC 20036
Phone: (202) 737-3600

 

Copyright © 2021 American Society for Microbiology | Privacy Policy | Website feedback

Print ISSN: 0095-1137; Online ISSN: 1098-660X