Incidence of moxifloxacin resistance in clinical Mycobacterium tuberculosis isolates in Houston, Texas.

Comprehensive data on the prevalence of quinolone resistance in Mycobacterium tuberculosis clinical isolates in the United States are scarce. By use of a systematic population-based approach, M. tuberculosis strains from tuberculosis (TB) cases were collected in Harris County, TX, in 2007 to 2008. The susceptibilities of M. tuberculosis isolates to moxifloxacin and ofloxacin were determined by the agar proportion indirect susceptibility method. Spoligotyping and 12-locus mycobacterial interspersed repetitive unit (MIRU12)-based genotyping of M. tuberculosis isolates were performed, and the gyrA, gyrB, Rv2686c, Rv2687c, and Rv2688c genes in quinolone-resistant and year-of-diagnosis-matched M. tuberculosis isolates were sequenced. Susceptibility testing was performed on 557 M. tuberculosis isolates, of which 10 (1.8%) were resistant to moxifloxacin. There was 100% concordance between ofloxacin and moxifloxacin susceptibilities. A quinolone was prescribed to at least 5 (50%) patients in the period preceding TB diagnosis. Multidrug-resistant TB (MDR-TB) was significantly associated with quinolone resistance (P = 0.01). Mutations in the quinolone resistance-determining region of gyrA were found for 50% of the resistant isolates. No other presumptive quinolone resistance-associated mutations were identified. We conclude that the incidence of moxifloxacin-resistant TB is low in Harris County and is associated with MDR-TB. Previous exposure to quinolones is common among patients with moxifloxacin resistance and warrants more careful evaluation.