Analysis of mutations in the gyrA and gyrB genes and their association with the resistance of Mycobacterium tuberculosis to levofloxacin, moxifloxacin and gatifloxacin

Chiu

et al. 2016

In order to correlate the mutations inside the entire gyrA and gyrB genes with the level of resistance to ofloxacin (OFX) and moxifloxacin (MFX) in isolates of multidrug-resistant Mycobacterium tuberculosis (MDR-TB), a total of 111 isolates were categorized into OFX-susceptible (MIC, <2 g/ml) and low-level (MIC, 4 to 8 g/ml) and high-level (MIC, >16 g/ml) OFX-resistant isolates and MFX-susceptible (MIC, <0.5 g/ml) and low-level (MIC, 1 to 2 g/ml) and high-level (MIC, >4 g/ml) MFXresistant isolates. Resistance-associated mutations inside the gyrA gene were found in 30.2% of OFX-susceptible and 72.5% and 72.2% of low-level and high-level OFX-resistant isolates and in 28.6% of MFX-susceptible and 58.1% and 83.9% of low-level and high-level MFX-resistant isolates. Compared with OFX-susceptible isolates, low-level and high-level OFX-resistant isolates had a significantly higher prevalence of mutations at gyrA codons 88 to 94 (17.0%, 65.0%, and 72.2%, respectively; P < 0.001) and a higher prevalence of the gyrB G512R mutation (0.0%, 2.5%, and 16.7%, respectively; P ‫؍‬ 0.006). Similarly, compared with MFXsusceptible isolates, low-level and high-level MFX-resistant isolates had a significantly higher prevalence of mutations at gyrA codons 88 to 94 (14.3%, 51.6%, and 80.6%, respectively; P < 0.001) as well as a higher prevalence of the gyrB G512R mutation (0.0%, 0.0%, and 12.9%, respectively; P ‫؍‬ 0.011). D94G and D94N mutations in gyrA and the G512R mutation in gyrB were correlated with high-level MFX resistance, while the D94A mutation was associated with low-level MFX resistance. The prevalence of mutations at gyrA codons 88 to 94 and the gyrB G512R mutation were higher among fluoroquinolone (FQ)-susceptible East Asian (Beijing) and Indo-Oceanic strains than they were among Euro-American strains, implying that molecular techniques to detect FQ resistance may be less specific in areas with a high prevalence of East Asian (Beijing) and Indo-Oceanic strains. F luoroquinolones (FQs) are used as second-line drugs for the treatment of tuberculosis (TB). These broad-spectrum antibacterial agents with bactericidal activity against Mycobacterium tuberculosis exert their bactericidal effects by inhibiting mycobacterial DNA gyrase activity, which prevents bacterial DNA from unwinding and replicating (1-3).Moxifloxacin (MFX), a "fourth-generation" FQ, has been shown to have better activity against M. tuberculosis than ofloxacin (OFX) and is recommended by the World Health Organization (WHO) for the treatment of multidrug-resistant TB (MDR-TB; defined as resistant to at least two of the most effective antituberculosis drugs, isoniazid and rifampin) (2, 3). Unfortunately, the widespread use of FQs to treat bacterial infections has led to the emergence of FQ-resistant MDR-TB and extensively drug-resistant TB (XDR-TB; defined as MDR-TB resistant to any FQ and a second-line injectable drug) (4, 5), thereby complicating patient care.Mutations in genes encoding DNA gyrase subunits gyrA and gyrB are the most common mechanism conveying ...

Section: Discussionmentioning

confidence: 56%

Mutations in gyrA and gyrB among Fluoroquinolone- and Multidrug-Resistant Mycobacterium tuberculosis Isolates

Chiu

et al. 2016

“…The MIC was defined as the lowest concentration of antibiotic that reduced the viability of the culture by at least 90% as determined by fluorescence measurements at room temperature in top-reading mode, in which the excitation wavelength and emission wavelength were 530 nm and 590 nm, respectively. The MIC breakpoints were defined as 2 g/ml for OFX and LFX and 0.5 g/ml for MOX, GAT, and SPX (18,19).…”

Section: Methodsmentioning

confidence: 99%

Prevalence and Molecular Characterization of Fluoroquinolone-Resistant Mycobacterium tuberculosis Isolates in China

Zhang

Wang

et al. 2014

China is one of the countries with the highest burdens of multidrug-resistant (MDR) and fluoroquinolone (FQ)-resistant tuberculosis (TB) globally. Nevertheless, knowledge about the prevalence and molecular characterization of FQ-resistant Mycobacterium tuberculosis isolates from this region remains scant. In this study, 138 M. tuberculosis isolates determined by the agar proportion susceptibility method to be resistant to ofloxacin (OFX) were enrolled from a national drug resistance survey of China. All these strains were tested for susceptibility to ofloxacin, levofloxacin, moxifloxacin, gatifloxacin, and sparfloxacin using liquid Middlebrook 7H9 medium. The entire gyrA and gyrB genes conferring FQ resistance were sequenced, and spoligotyping was performed to distinguish different genotypes. Overall, the prevalence of resistance in China was highest for ofloxacin (3.76%), intermediate for levofloxacin (3.18%) and moxifloxacin (3.12%), and lowest for sparfloxacin (1.91%) and gatifloxacin (1.33%). Mutations in the gyrA gene were observed in 89 (64.5%) out of the 138 OFX-resistant M. tuberculosis strains. Positions 94 and 90 were the most frequent sites of mutation conferring FQ resistance on these strains, accounting for high-level FQ resistance. Furthermore, the Beijing genotype showed no association with high-level FQ resistance or distribution in hot spots in the quinolone resistance-determining region (QRDR) of gyrA. Our findings provide essential implications for the feasibility of genotypic tests relying on detection of mutations in the QRDR of gyrA and the shorter first-line treatment regimens based on FQs in China.

“…Cross-resistance exists between fluoroquinolones, and mutations that emerge under ofloxacin treatment are usually associated with moxifloxacin MICs above the WHO-defined critical concentration of 0.25 g/ml (4). However, 84 to 98% of isolates with mutations conferring fluoroquinolone resistance have MICs of Յ2 g/ml for moxifloxacin, which does not necessarily reflect clinical resistance (3,(5)(6)(7)(8)(9). Based on this, an alternative critical concentration of 2 g/ml has been suggested (5,6,10).…”

mentioning

confidence: 99%

Moxifloxacin Retains Antimycobacterial Activity in the Presence of gyrA Mutations

McGrath

Pittius

Sirgel

et al. 2014

Moxifloxacin-resistant Mycobacterium tuberculosis mutants were selected in vitro using different concentrations of moxifloxacin. gyrA mutations at codons 88 and 94 were associated with resistance (defined as an MIC of >2 g/ml) (P < 0.0001 and P ‫؍‬ 0.0053, respectively). Despite the presence of gyrA mutations, moxifloxacin significantly impedes bacterial growth, supporting its use for the treatment of ofloxacin-resistant M. tuberculosis.