Role of gyrB Mutations in Pre-extensively and Extensively Drug-Resistant Tuberculosis in Thai Clinical Isolates

Abstract

DNA gyrase mutations are a major cause of quinolone resistance in Mycobacterium tuberculosis. We therefore conducted the first comprehensive study to determine the diversity of gyrase mutations in pre-extensively drug-resistant (pre-XDR) (n ‫؍‬ 71) and extensively drug-resistant (XDR) (n ‫؍‬ 30) Thai clinical tuberculosis (TB) isolates. All pre-XDR-TB and XDR-TB isolates carried at least one mutation within the quinolone resistance-determining region of GyrA ( . MIC and DNA gyrase supercoiling inhibition assays were performed to determine the role of gyrase mutations in quinolone resistance. Compared to the MICs against M. tuberculosis H37Rv, the levels of resistance to all quinolones tested in the isolates that carried GyrA-D94G or GyrB-N538D (8-to 32-fold increase) were significantly higher than those in isolates bearing GyrA-D94A or GyrA-A90V (2-to 8-fold increase) (P < 0.01). Intriguingly, GyrB-E540D led to a dramatic resistance to later-generation quinolones, including moxifloxacin, gatifloxacin, and sparfloxacin (8-to 16-fold increases in MICs and 8.3-to 11.2-fold increases in 50% inhibitory concentrations [IC 50 s]). However, GyrB-E540D caused low-level resistance to early-generation quinolones, including ofloxacin, levofloxacin, and ciprofloxacin (2-to 4-fold increases in MICs and 1.5-to 2.0-fold increases in IC 50 s). In the present study, DC159a was the most active antituberculosis agent and was little affected by the gyrase mutations described above. Our findings suggest that although they are rare, gyrB mutations have a notable role in quinolone resistance, which may provide clues to the molecular basis of estimating quinolone resistance levels for drug and dose selection.

The epidemiology, pathogenesis, transmission, diagnosis, and management of multidrug-resistant, extensively drug-resistant, and incurable tuberculosis

“…Confirmation of these lower critical concentrations have come from clinical studies [209][210][211][212][213] and several investigations [214][215][216][217][218][219][220][221] of drug resistance-associated mutations in isolates with MICs below the standard breakpoint. Clinical studies using assumption-free methods such as machine learning have confirmed that these values (table 3) are in fact the MICs above which tuberculosis patients fail combination therapy.…”

“…Additionally, studies have been done in which treatment failed in patients who were infected with M tuberculosis who had drug target site mutations, but MICs were lower than current breakpoints, and were more consistent with the newly proposed breakpoints. [214][215][216][217][218][219][220][221] Therefore, the proposed concentrations have higher sensitivity for clinical decision making, and should be used to estimate the global burden of MDR tuberculosis.…”

A Review of Moxifloxacin for the Treatment of Drug‐Susceptible Tuberculosis

“…Two studies in South Africa 92,97 found that mutations at common codons 90 and 94 resulted in increases in MIC up to 2.00 mg/L, and studies in China and Thailand with similar findings also reported much higher MICs of up to 16.00 mg/L in a small percentage of patients with these and other mutations. 98,99 A recent survey conducted in South Africa, Eastern Europe, and Asia found that resistance was between 0.9% and 14.6% for moxifloxacin when tested at 0.50 mg/L and much lower in all countries when tested at 2.00 mg/L. 94 The study also determined resistance to moxifloxacin among patients with rifampicin-sensitive and rifampicinresistant isolates.…”

In Vitro Activity and MIC of Sitafloxacin against Multidrug-Resistant and Extensively Drug-Resistant Mycobacterium tuberculosis Isolated in Thailand

“…In contrast, mutations in the QRDR of gyrB, although found much less frequently (Յ2%) than the gyrA mutations, showed different MIC levels among the quinolones. The GyrB Glu540Asp mutation has been shown to mediate higher MICs of later quinolones, particularly 8-methoxy quinolones like MOFX, than of early quinolones (12). In this study, the gyrA and gyrB genes of 53 OFX-resistant strains were sequenced.…”