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Susceptibility to levofloxacin of Mycobacterium tuberculosis isolates from patients with HIV‐related tuberculosis and characterization of a strain with levofloxacin monoresistance

Objective:To characterize the susceptibility to levofloxacin of clinical isolates of Mycobacterium tuberculosis (MTB) obtained from patients with HIV-related tuberculosis and to characterize the molecular genetics of levofloxacin resistance. Design and methods:Isolates from culture-positive patients in a United States multicenter trial of HIV-related TB were tested for susceptibility to levofloxacin by minimum inhibitory concentration (MIC) determinations in Bactec 7H12 broth. Automated sequencing of the resistance determining region of gyrA was performed. Results:Of the 135 baseline MTB isolates tested, 134 (99%; 95% exact binomial confidence interval, 95.9–99.9%) were susceptible to levofloxacin with an MIC ≤ 1.0 µg/ml. We identified a previously unrecognized mis-sense mutation occurring at codon 88 of gyrA in a levofloxacin mono-resistant MTB isolate obtained from a patient with AIDS who had received ofloxacin for 8 months prior to the diagnosis of tuberculosis. Conclusions:Clinical MTB isolates from HIV-infected patients were generally susceptible to levofloxacin. However, the identification of a clinical isolate with mono-resistance to levofloxacin highlights the need for circumspection in the use of fluoroquinolones in the setting of potential HIV-related tuberculosis and for monitoring of rates of resistance of MTB isolates to fluoroquinolones.