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Susceptibility testing breakpoints for Mycobacterium tuberculosis categorize isolates with resistance mutations in gyrA as susceptible to fluoroquinolones: implications for MDR-TB treatment and the definition of XDR-TB.
Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Infectious Diseases.
Karolinska University Hospital, Stockholm, Sweden. The University of the West Indies, Kingston, Jamaica.
Karolinska University Hospital, Stockholm, Karolinska Institute, Stockholm, Sweden..
Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Infectious Diseases.
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2016 (English)In: Journal of Antimicrobial Chemotherapy, ISSN 0305-7453, E-ISSN 1460-2091, Vol. 71, no 2, 333-338 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: Fluoroquinolones (FQs) are important in the treatment of MDR-TB and in the definition of XDR-TB. Our objective was to investigate how discrepancies in the phenotypic and genotypic methods for antimicrobial susceptibility testing could affect the interpretation of antimicrobial susceptibility test results.

METHODS: We analysed MICs of ofloxacin and levofloxacin in Middlebrook 7H10 broth (7H10) as well as sequencing of the quinolone resistance-determining region of the gyrA gene and the MTBDRsl assay in 75 resistant isolates, including MDR and XDR strains of Mycobacterium tuberculosis.

RESULTS: Among 75 resistant isolates, 27 had mutations associated with FQ resistance. Among isolates with resistance mutations in gyrA, 26% (seven of 27) were susceptible to levofloxacin and ofloxacin by phenotypic testing at 1 mg/L and 2 mg/L. The most common mutation was in codon 94 and these isolates had significantly increased MICs of levofloxacin (2-8 mg/L) compared with isolates with mutations in codon 90 (0.25-2 mg/L, P < 0.05). The sensitivity and specificity for the MTBDRsl assay compared with gyrA sequencing were 96% and 98%, respectively.

CONCLUSION: Current critical concentrations may classify up to 26% of isolates with gyrA mutations as susceptible to FQs due to a close relationship between susceptible and resistant populations. These results should be considered while improving clinical breakpoints for M. tuberculosis and may have an impact on the definition of XDR-TB.

Place, publisher, year, edition, pages
2016. Vol. 71, no 2, 333-338 p.
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Infectious Medicine
Identifiers
URN: urn:nbn:se:liu:diva-124557DOI: 10.1093/jac/dkv353ISI: 000372427600008PubMedID: 26538509OAI: oai:DiVA.org:liu-124557DiVA: diva2:900057
Note

Funding agencies: Heart and Lung Foundation; Swedish Society of Antimicrobial Chemotherapy (SSAC); Swedish Medical Association; Marianne and Marcus Wallenberg Foundation

Available from: 2016-02-03 Created: 2016-02-03 Last updated: 2016-04-20

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Niward, KatarinaPaues, JakobSchön, Thomas
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Division of Microbiology and Molecular MedicineFaculty of Medicine and Health SciencesDepartment of Infectious Diseases
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