Skip to content
1887

Journal of Medical Microbiology logo Journal of Medical Microbiology

Volume 74, Issue 10

The lingering legacy of one letter in antimicrobial susceptibility testing Open Access

Abstract

For decades, the ‘Intermediate’ (I) category in antimicrobial susceptibility testing was frequently misinterpreted as indicative of therapeutic failure, rather than an opportunity for dose optimization. This misunderstanding shaped prescribing behaviour, antimicrobial trial design and guideline development. The 2019 European Committee on Antimicrobial Susceptibility Testing redefinition of the ‘I’ category as ‘Susceptible, Increased Exposure’ (SIE) highlighted the potential for treatment efficacy through dose adjustment, challenging entrenched prescribing behaviours and exposing limitations in historical trials, guidelines and surveillance practices. Antimicrobial stewardship that employs SIE-based strategies can preserve narrower-spectrum agents. However, the misapplication of ‘I’ can promote unnecessary broad-spectrum antimicrobial prescribing. Surveillance systems, clinical decision support and antimicrobial stewardship should be continuously updated to reflect current pharmacological principles and thereby enhance patient care outcomes.

  • Received:
  • Accepted:
  • Published Online:
Keyword(s): antimicrobial stewardship , antimicrobial susceptibility testing , dose optimization , European Committee on Antimicrobial Susceptibility Testing (EUCAST) , intermediate category and susceptible increased exposure
© 2025 The Authors
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License. This article was made open access via a Publish and Read agreement between the Microbiology Society and the corresponding author’s institution.
Loading

Article metrics loading...

/content/journal/jmm/10.1099/jmm.0.002082
2025-10-07
2025-11-13

Metrics

Loading full text...

Full text loading...

/deliver/fulltext/jmm/74/10/jmm002082.html?itemId=/content/journal/jmm/10.1099/jmm.0.002082&mimeType=html&fmt=ahah

References

  1. European Committee on Antimicrobial Susceptibility Testing Definitions of S, I and R. n.d https://www.eucast.org/newsiandr accessed 16 July 2025
  2. Aupaix A, Mzougui S, Soleimani R. Impact of susceptible, increased exposure, a new definition of the former intermediate susceptibility category, introduced by the European Committee for Antimicrobial Susceptibility Testing on antimicrobial susceptibility testing evaluation. Clin Microbiol Infect 2024; 30:1494–1496 [View Article] [PubMed]
     [Google Scholar]
  3. Wantia N, Gatermann SG, Rothe K, Laufenberg R. New EUCAST definitions of S, I and R from 2019 - German physicians are largely not aware of the changes. Infection 2020; 48:597–606 [View Article] [PubMed]
     [Google Scholar]
  4. Munting A, Regina J, Damas J, Lhopitallier L, Kritikos A et al. Impact of 2020 EUCAST criteria on meropenem prescription for the treatment of Pseudomonas aeruginosa infections: an observational study in a university hospital. Clin Microbiol Infect 2022; 28:558–563 [View Article] [PubMed]
     [Google Scholar]
  5. Ourghanlian C, Fihman V, Morel A, Lafont C, Galy A et al. Overly broad-spectrum antibiotic treatment of wild-type Pseudomonas aeruginosa infections in relation to the EUCAST new definition of susceptibility testing categories, a retrospective multicentre cohort study. JAC Antimicrob Resist 2022; 4:dlac099 [View Article] [PubMed]
     [Google Scholar]
  6. Munting A, Damas J, Viala B, Prod’hom G, Guery B et al. Impact of selective reporting of antibiotic susceptibility testing results on meropenem prescriptions for the treatment of Pseudomonas aeruginosa infections after 2020 EUCAST criteria update: an observational study in a university hospital. Antimicrob Resist Infect Control 2022; 11:165 [View Article]
     [Google Scholar]
  7. Kawalec A, Józefiak J, Kiliś-Pstrusińska K. Urinary tract infection and antimicrobial resistance patterns: 5-year experience in a tertiary pediatric nephrology center in the southwestern region of Poland. Antibiotics 2023; 12:1454 [View Article] [PubMed]
     [Google Scholar]
  8. Herrmann J, Burgener-Gasser A-V, Goldenberger D, Roth J, Weisser M et al. Cefepime versus carbapenems for treatment of AmpC beta-lactamase-producing Enterobacterales bloodstream infections. Eur J Clin Microbiol Infect Dis 2024; 43:213–221 [View Article] [PubMed]
     [Google Scholar]
  9. Bosman AL, Uhland F, Agunos A, Carson CA. One Health surveillance of antimicrobial resistance and use by the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS). Can Vet J 2024; 65:1081–1085 [PubMed]
     [Google Scholar]
  10. ResistanceMap. One Health Trust. n.d https://resistancemap.onehealthtrust.org/ accessed 15 July 2025
/content/journal/jmm/10.1099/jmm.0.002082
Loading

Most cited Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An error occurred
Approval was partially successful, following selected items could not be processed due to error