title: gyrA mutations and phenotypic susceptibility levels to ofloxacin and moxifloxacin in clinical isolates of Mycobacterium tuberculosis.
abstract: OBJECTIVE
  To compare mutations in the quinolone resistance-determining region of the gyrA gene and flanking sequences with the MICs of ofloxacin and moxifloxacin for Mycobacterium tuberculosis.
  
  
  METHODS
  The presence of mutations in 177 drug-resistant M. tuberculosis isolates was determined by DNA sequencing and the MICs quantified by MGIT 960.
  
  
  RESULTS
  Single nucleotide polymorphisms were detected at codons 94 (n = 30), 90 (n = 12), 91 (n = 3), 89 (n = 1), 88 (n = 1) and 80 (n = 1). Four isolates with double mutations D94G plus A90V (n = 2) and D94G plus D94N (n = 2) reflect mixed populations. Agreement between genotypic and phenotypic susceptibility was high (≥97%) for both drugs. Mutant isolates had an MIC(50) of 8.0 mg/L and an MIC(90) of >10 mg/L for ofloxacin compared with an MIC(50) and MIC(90) of 2.0 mg/L for moxifloxacin. Codons 94 and 88 were linked to higher levels of fluoroquinolone resistance compared with codons 90, 91 and 89. The MIC distributions for the wild-type isolates ranged from ≤0.5 to 2.0 mg/L for ofloxacin and from ≤0.125 to 0.25 mg/L for moxifloxacin. However, 96% of the isolates with genetic alterations had MICs ≤2.0 mg/L for moxifloxacin, which is within its achievable serum levels.
  
  
  CONCLUSIONS
  This study provides quantitative evidence that the addition of moxifloxacin to extensively drug-resistant tuberculosis (XDR-TB) regimens based on a clinical breakpoint of 2.0 mg/L has merit. The use of moxifloxacin in the treatment of multidrug-resistant tuberculosis may prevent the acquisition of additional mutations and development of XDR-TB.
authors.affiliation: DST/NRF Centre of Excellence for Biomedical TB Research/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Faculty of Health Science, Stellenbosch University, Stellenbosch, South Africa. fas@sun.ac.za
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Sirgel
authors.forename: Robin M
authors.initials: RM
authors.lastname: Warren
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Streicher
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Victor
authors.forename: Paul D
authors.initials: PD
authors.lastname: van Helden
authors.forename: Erik C
authors.initials: EC
authors.lastname: Böttger
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001372:Aza Compounds / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics*; D024881:Drug Resistance, Bacterial; D024841:Fluoroquinolones; D006801:Humans; D008826:Microbial Sensitivity Tests; D000077266:Moxifloxacin; D020125:Mutation, Missense; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics; D015242:Ofloxacin / Q000494:pharmacology*; D020641:Polymorphism, Single Nucleotide; D011804:Quinolines / Q000494:pharmacology*
chemical_list: D000995:Antitubercular Agents; D001372:Aza Compounds; D024841:Fluoroquinolones; D011804:Quinolines; D015242:Ofloxacin; D027081:DNA Gyrase; D000077266:Moxifloxacin