Beijing Genotype of Mycobacterium tuberculosis Is Significantly Associated with High-Level Fluoroquinolone Resistance in Vietnam

Consecutive fluoroquinolone (FQ)-resistant isolates (n = 109) identified at the Pham Ngoc Thach Hospital for Tuberculosis, Ho Chi Minh City, Vietnam, were sequenced in the quinolone resistance-determining regions of the gyrA and gyrB genes and typed by large sequence polymorphism typing and spoligotyping to identify the Beijing genotype of Mycobacterium tuberculosis. Beijing genotype prevalence was compared with 109 consecutive isolates from newly presenting patients with pulmonary tuberculosis from the hospital outpatient department. Overall, 82.6% (n = 90/109) of isolates had mutations in gyrAB. Nine novel mutations were identified in gyrB (S486F, N538T, T539P, D500A, D500H, D500N, G509A, E540V, and E540D). The influence of these novel gyrB mutations on FQ resistance is not proven. The Beijing genotype was significantly associated with FQ resistance (odds ratio [OR], 2.39 [95% confidence interval {CI}, 1.34 to 4.25]; P = 0.003). Furthermore, Beijing genotype FQ-resistant isolates were significantly more likely than FQ-resistant isolates of other genotypes to have gyrA mutations (OR, 7.75 [95% CI, 2.84 to 21.15]; P = 0.0001) and high-level (>8 μg/ml) FQ resistance (OR, 11.0 [95% CI, 2.6 to 47.0]; P = 0.001). The underlying mechanism of the association of the Beijing genotype with high-level FQ resistance in this setting remains to be determined. The association of the Beijing genotype with relatively high-level FQ resistance conferred by specific gyrA mutations reported here is of grave concern given the epidemic spread of the Beijing genotype and the current hopes for shorter first-line treatment regimens based on FQs.Fluoroquinolones (FQs) are the most promising antituberculous therapeutic agents to be developed in 40 years (9, 31). They are widely used for the treatment of multidrug-resistant (MDR) tuberculosis (TB) despite the lack of clinical trials evaluating optimal doses, duration, and combinations (10, 28, 31). Gatifloxacin is currently in phase III trials as a first-line agent to shorten existing treatment regimens from 6 to 4 months (ClinicalTrials.gov identification number {"type":"clinical-trial","attrs":{"text":"NCT00216385","term_id":"NCT00216385"}}NCT00216385 [http://clinicaltrials.gov/ct2/show/{"type":"clinical-trial","attrs":{"text":"NCT00216385","term_id":"NCT00216385"}}NCT00216385]), and moxifloxacin is in phase III trials as a first-line substitute for either ethambutol (ETH) (ClinicalTrials.gov identification number {"type":"clinical-trial","attrs":{"text":"NCT00082173","term_id":"NCT00082173"}}NCT00082173 [http://clinicaltrials.gov/show/{"type":"clinical-trial","attrs":{"text":"NCT00082173","term_id":"NCT00082173"}}NCT00082173]) or isoniazid (INH) (ISRCTN register number 85595810 [http://www.controlled-trials.com/ISRCTN85595810]; ClinicalTrials.gov identification number {"type":"clinical-trial","attrs":{"text":"NCT00144417","term_id":"NCT00144417"}}NCT00144417 [www.clinicaltrials.gov/show/{"type":"clinical-trial","attrs":{"text":"NCT00144417","term_id":"NCT00144417"}}NCT00144417]).There is concern about levels of preexisting FQ-resistant TB in regions with high drug resistance rates because these drugs are often available over the counter and are additionally prescribed as broad-spectrum antibiotics for the treatment of undiagnosed respiratory infections (4, 5, 11, 17, 23, 27, 29).Vietnam has some of the highest primary drug resistance rates for Mycobacterium tuberculosis in the world, with over 35% of primary isolates being resistant to one or more first-line drugs (21, 26). Despite this, MDR TB rates remain relatively low, at 2.7% nationally, and the National Tuberculosis Program has achieved World Health Organization (WHO) targets for the detection and cure of TB for the last 10 years (14). An expanded MDR TB management program (formally DOTS-PLUS) will be piloted in the near future; however, the success of standardized regimens will depend heavily on preexisting levels of resistance to the most effective second-line agents, the FQs. At present, no data exist on FQ-resistant TB in Vietnam.In mycobacteria, the FQs bind to DNA gyrase and inhibit DNA replication. Reports in the literature show that the majority (approximately 60%) of FQ-resistant M. tuberculosis isolates carry mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene, and a small number have mutations in the gyrB gene (10). It was previously postulated that efflux pump mechanisms account for FQ resistance in isolates with wild-type gyrAB genes (6).While adherence remains the single most important factor in the emergence of drug-resistant TB, a factor contributing to the high prevalence of INH and streptomycin (STR) resistance in the region may be the high prevalence of strains of Mycobacterium tuberculosis of the Beijing genotype (1-3). The Beijing genotype first attracted attention as being the genotype of the strain responsible (W strain) for several large outbreaks of MDR TB in the United States in the early 1990s (28). It is associated with drug resistance and MDR in Vietnam (1, 3).This study investigated the prevalence of the Beijing genotype among FQ-resistant isolates from southern Vietnam and the associated genotypic mutations and MICs of ofloxacin.