Validation of EUCAST 2026 breakpoints for Brucella species using routine laboratory methods: A comprehensive French National Reference Centre study
- 1Virulence Bactérienne et Infections Chroniques, INSERM U1047, Univ Montpellier, Service de Microbiologie et Hygiène Hospitalière, Centre National de Référence des Brucelloses, CHU Nîmes, Nîmes, France
- 2Virulence Bactérienne et Infections Chroniques, INSERM U1047, Univ Montpellier, Service des Maladies Infectieuses et Tropicales, Centre National de Référence des Brucelloses, CHU Nîmes, Nîmes, France
Abstract
Brucellosis, caused by various species of the bacterial genus Brucella, represents a significant global health burden in many parts of the world. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) recently established standardized clinical breakpoints (version 16.1, 2026) for Brucella to support global surveillance and evidence-based treatment. This study validates EUCAST 2026 breakpoints using routine laboratory methods in a large national reference collection. We retrospectively analyzed 234 Brucella isolates from the French National Reference Centre between January 2017 and June 2026, using MALDI-TOF mass spectrometry and multiplex PCR for species identification, and E-test strips and disk diffusion for antimicrobial susceptibility testing (AST) according to EUCAST guidelines. Brucella melitensis predominated (n = 210, 89.7%), with smaller numbers of B. suis, B. abortus, and B. amazoniensis. Universal susceptibility was observed across all 234 isolates for eight tested antibiotics. Notably, 49.6% of isolates displayed rifampicin minimum inhibitory concentrations (MICs) within two doubling dilutions of the EUCAST epidemiological cut-off (ECOFF) value, highlighting the need for continued surveillance of rifampicin susceptibility in this genus. A critical methodological finding emerged regarding streptomycin assessment. E-test strips indicated elevated streptomycin MICs in a substantial proportion of isolates, with results consistent across different lots. However, disk diffusion performed on identical isolates demonstrated universal susceptibility for all 234 isolates, with inhibition zone diameters ranging from 21–35 mm. This study validates that EUCAST 2026 breakpoints are clinically appropriate and epidemiologically sound when applied using appropriate routine laboratory methods. Disk diffusion should be considered the reference method for streptomycin susceptibility determination in Brucella species. These findings provide essential practical guidance for clinical microbiology laboratories, demonstrate that France remains free from antimicrobial resistance, and support standardized AST testing for optimized management of human brucellosis in both endemic and non-endemic regions worldwide. Author summary: Brucellosis is a serious infectious disease that affects livestock and spreads to humans through contact with infected animals or contaminated animal products. The disease is particularly common in Africa and the Middle East but can occur anywhere due to travel and trade. To treat brucellosis effectively, it is needed to know which antibiotics work best against the bacteria causing the disease. In this study, we tested 234 bacterial samples collected in France over eight years to determine which antibiotics were most effective. We found that all bacteria tested remained susceptible to our standard antibiotics. However, we discovered an important problem: one testing method commonly used in laboratories gave misleading results for one antibiotic called streptomycin. When we used a different, more reliable testing method, we confirmed that streptomycin still works well against these bacteria. Our findings help laboratories choose the best testing methods and confirm that the international treatment guidelines being used are working well. Additionally, we found that half of the bacteria had antibiotic levels just below the danger zone, suggesting we need to continue monitoring for potential resistance in the future.
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BibTeX
@article{gaillard2026validation,
title = {{Validation of EUCAST 2026 breakpoints for Brucella species using routine laboratory methods: A comprehensive French National Reference Centre study}},
author = {Marie Gaillard and Théo Pastre and Chloé Magnan and Albert Sotto and David O’Callaghan and Anne Keriel and Jean-Philippe Lavigne},
journal = {PLOS Neglected Tropical Diseases},
year = {2026},
month = oct,
doi = {10.1371/journal.pntd.0014817},
url = {https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014817},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Validation of EUCAST 2026 breakpoints for Brucella species using routine laboratory methods: A comprehensive French National Reference Centre study
AU - Marie Gaillard
AU - Théo Pastre
AU - Chloé Magnan
AU - Albert Sotto
AU - David O’Callaghan
AU - Anne Keriel
AU - Jean-Philippe Lavigne
PY - 2026
DA - 2026/10/27
JO - PLOS Neglected Tropical Diseases
DO - 10.1371/journal.pntd.0014817
UR - https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014817
AB - Brucellosis, caused by various species of the bacterial genus Brucella, represents a significant global health burden in many parts of the world. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) recently established standardized clinical breakpoints (version 16.1, 2026) for Brucella to support global surveillance and evidence-based treatment. This study validates EUCAST 2026 breakpoints using routine laboratory methods in a large national reference collection. We retrospectively analyzed 234 Brucella isolates from the French National Reference Centre between January 2017 and June 2026, using MALDI-TOF mass spectrometry and multiplex PCR for species identification, and E-test strips and disk diffusion for antimicrobial susceptibility testing (AST) according to EUCAST guidelines. Brucella melitensis predominated (n = 210, 89.7%), with smaller numbers of B. suis, B. abortus, and B. amazoniensis. Universal susceptibility was observed across all 234 isolates for eight tested antibiotics. Notably, 49.6% of isolates displayed rifampicin minimum inhibitory concentrations (MICs) within two doubling dilutions of the EUCAST epidemiological cut-off (ECOFF) value, highlighting the need for continued surveillance of rifampicin susceptibility in this genus. A critical methodological finding emerged regarding streptomycin assessment. E-test strips indicated elevated streptomycin MICs in a substantial proportion of isolates, with results consistent across different lots. However, disk diffusion performed on identical isolates demonstrated universal susceptibility for all 234 isolates, with inhibition zone diameters ranging from 21–35 mm. This study validates that EUCAST 2026 breakpoints are clinically appropriate and epidemiologically sound when applied using appropriate routine laboratory methods. Disk diffusion should be considered the reference method for streptomycin susceptibility determination in Brucella species. These findings provide essential practical guidance for clinical microbiology laboratories, demonstrate that France remains free from antimicrobial resistance, and support standardized AST testing for optimized management of human brucellosis in both endemic and non-endemic regions worldwide. Author summary: Brucellosis is a serious infectious disease that affects livestock and spreads to humans through contact with infected animals or contaminated animal products. The disease is particularly common in Africa and the Middle East but can occur anywhere due to travel and trade. To treat brucellosis effectively, it is needed to know which antibiotics work best against the bacteria causing the disease. In this study, we tested 234 bacterial samples collected in France over eight years to determine which antibiotics were most effective. We found that all bacteria tested remained susceptible to our standard antibiotics. However, we discovered an important problem: one testing method commonly used in laboratories gave misleading results for one antibiotic called streptomycin. When we used a different, more reliable testing method, we confirmed that streptomycin still works well against these bacteria. Our findings help laboratories choose the best testing methods and confirm that the international treatment guidelines being used are working well. Additionally, we found that half of the bacteria had antibiotic levels just below the danger zone, suggesting we need to continue monitoring for potential resistance in the future.
SN - 1935-2735
SN - 1935-2727
ER -