Rapid Acquisition and Transmission of Drug Resistance Amongst Beijing Lineage Mycobacterium tuberculosis in Vietnam

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Whole genome sequencing (WGS) and phenotypic drug susceptibility testing was performed on a collection of 2,542 Mycobacterium tuberculosis (Mtb) isolates from tuberculosis (TB) patients recruited in Ho Chi Minh City (HCMC), Vietnam, to investigate Mtb diversity, the prevalence and phylodynamics of drug resistance, and in silico resistance prediction with sequencing data. Amongst isolates tested phenotypically against first-line drugs, we observed high rates of streptomycin [STR, 37.7% (N=573/1,520)] and isoniazid resistance [INH, 25.7% (N=459/1,786)], and lower rates of resistance to rifampicin [RIF, 4.9% (N=87/1,786)] and ethambutol [EMB, 4.2% (N=75/1,785)]. Resistance to STR and INH was predicted moderately well when applying the TB-Profiler algorithm to WGS data (sensitivities of 0.81 and 0.87 respectively), while resistance to RIF and EMB was predicted relatively poorly (sensitivities of 0.70 and 0.44 respectively). Rates of multidrug-resistance [(MDR, 3.9% (N=69/1,786)], and resistance to a number of second-line drugs [Para-aminosalicylic acid (29.6% N=79/267), Amikacin (15.4% N=41/267) and Moxifloxacin (21.3%), N=57/267], were found to be high within a global context. Comparing rates of drug resistance among lineages, and exploring the dynamics of resistance acquisition through time, suggest the Beijing lineage (lineage 2.2) acquires de novo resistance mutations at higher rates and suffers no apparent fitness cost acting to impede the transmission of resistance. We infer resistance to INH and STR to have arisen earlier, on average, than resistance to RIF, and to be more widespread across the phylogeny. The high prevalence of ‘background’ INH resistance, combined with high rates of RIF mono-resistance (20.7%, N=18/87) suggests that rapid assays for INH resistance will be valuable in this setting. These tests will allow the detection of INH mono-resistance, and will allow MDR isolates to be distinguished from isolates with RIF mono-resistance.

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