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A new rapid resazurin-based microdilution assay for antimicrobial susceptibility testing of Neisseria gonorrhoeae

Foerster, Sunniva ; Desilvestro, Valentino ; Hathaway, Lucy J. ; Althaus, Christian L. ; Unemo, Magnus

In: Journal of Antimicrobial Chemotherapy, 2017, vol. 72, no. 7, p. 1961-1968

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    Titre
    • A new rapid resazurin-based microdilution assay for antimicrobial susceptibility testing of Neisseria gonorrhoeae
    Auteur
    • Foerster, Sunniva. Institute for Infectious Diseases, University of Bern, Bern, Switzerland
    • Desilvestro, Valentino. World Trade Institute (WTI), University of Bern, Bern, Switzerland
    • Hathaway, Lucy J.. Institute for Infectious Diseases, University of Bern, Bern, Switzerland
    • Althaus, Christian L.. Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland
    • Unemo, Magnus. WHO Collaborating Centre for Gonorrhoea and other STIs, Örebro University, Örebro, Sweden
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Journal of Antimicrobial Chemotherapy, 2017, vol. 72, no. 7, p. 1961-1968. Oxford University Press
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:332964
    Summary
    Objectives: Rapid, cost-effective and objective methods for antimicrobial susceptibility testing of Neisseria gonorrhoeae would greatly enhance surveillance of antimicrobial resistance. Etest, disc diffusion and agar dilution methods are subjective, mostly laborious for large-scale testing and take ∼24 h. We aimed to develop a rapid broth microdilution assay using resazurin (blue), which is converted into resorufin (pink fluorescence) in the presence of viable bacteria. Methods: The resazurin-based broth microdilution assay was established using 132 N. gonorrhoeae strains and the antimicrobials ceftriaxone, cefixime, azithromycin, spectinomycin, ciprofloxacin, tetracycline and penicillin. A regression model was used to estimate the MICs. Assay results were obtained in ∼7.5 h. Results: The EC50 of the dose-response curves correlated well with Etest MIC values (Pearson's r = 0.93). Minor errors resulting from misclassifications of intermediate strains were found for 9% of the samples. Major errors (susceptible strains misclassified as resistant) occurred for ceftriaxone (4.6%), cefixime (3.3%), azithromycin (0.6%) and tetracycline (0.2%). Only one very major error was found (a ceftriaxone-resistant strain misclassified as susceptible). Overall the sensitivity of the assay was 97.1% (95% CI 95.2-98.4) and the specificity 78.5% (95% CI 74.5-82.9). Conclusions: A rapid, objective, high-throughput, quantitative and cost-effective broth microdilution assay was established for gonococci. For use in routine diagnostics without confirmatory testing, the specificity might remain suboptimal for ceftriaxone and cefixime. However, the assay is an effective low-cost method to evaluate novel antimicrobials and for high-throughput screening, and expands the currently available methodologies for surveillance of antimicrobial resistance in gonococci.