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A new rapid resazurin-based microdilution assay for antimicrobial susceptibility testing of Neisseria gonorrhoeae
Institute for Infectious Diseases, University of Bern, Bern, Switzerland; Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland; WHO Collaborating Centre for Gonorrhoea and other STIs, Örebro University, Örebro, Sweden; Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
World Trade Institute (WTI), University of Bern, Bern, Switzerland.
Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
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2017 (English)In: Journal of Antimicrobial Chemotherapy, ISSN 0305-7453, E-ISSN 1460-2091, Vol. 72, no 7, 1961-1968 p.Article in journal (Refereed) Published
Abstract [en]

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 EC 50 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.

Place, publisher, year, edition, pages
Oxford University Press, 2017. Vol. 72, no 7, 1961-1968 p.
National Category
Pharmacology and Toxicology Infectious Medicine
Identifiers
URN: urn:nbn:se:oru:diva-57314DOI: 10.1093/jac/dkx113ISI: 000404901100017PubMedID: 28431096Scopus ID: 2-s2.0-85021821642OAI: oai:DiVA.org:oru-57314DiVA: diva2:1103817
Note

Funding Agencies:

Interdisciplinary PhD (IPhD) project from SystemsX.ch (The Swiss Initiative for Systems Biology)  

RaDAR-Go (RApid Diagnosis of Antibiotic Resistance in Gonorrhoea - Swiss Platform for Translational Medicine)  

Örebro County Council Research Committee  

Foundation for Medical Research at Örebro University Hospital, Sweden 

Available from: 2017-05-31 Created: 2017-05-31 Last updated: 2017-10-18Bibliographically approved

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