Intragenic Distribution of IS 6110 in Clinical Mycobacterium tuberculosis Strains: Bioinformatic Evidence for Gene Disruption Leading to Underdiagnosed Antibiotic Resistance

Abstract

To help control the spread of drug-resistant tuberculosis and to guide treatment choices, it is important that rapid and accurate molecular diagnostic tools are used. Current molecular diagnostic tools detect the most common antibiotic-resistance-conferring mutations in the form of single nucleotide changes, small deletions, or insertions. Antibiotic resistance is a global challenge for tuberculosis control, and accelerating its diagnosis is critical for therapy decisions and controlling transmission. Genotype-based molecular diagnostics now play an increasing role in accelerating the detection of such antibiotic resistance, but their accuracy depends on the instructed detection of genetic variations. Genetic mobile elements such as IS 6110 are established sources of genetic variation in Mycobacterium tuberculosis , but their implication in clinical antibiotic resistance has thus far been unclear. Here, we describe the discovery of an intragenic IS 6110 insertion into Rv0678 that caused antibiotic resistance in an in vitro -selected M. tuberculosis isolate. The subsequent development of bioinformatics scripts allowed genome-wide analysis of intragenic IS 6110 insertions causing gene disruptions in 6,426 clinical M. tuberculosis strains. This analysis identified 10,070 intragenic IS 6110 insertions distributed among 333 different genes. Focusing on genes whose disruption leads to antibiotic resistance, 12 clinical isolates were identified with high confidence to be resistant to bedaquiline, clofazimine, pyrazinamide, ethionamide, and para -aminosalicylic acid because of an IS 6110 -mediated gene disruption event. A number of these IS 6110 -mediated resistant strains had identical genomic distributions of IS 6110 elements and likely represent transmission events of a single resistant isolate. These data provide strong evidence that IS 6110 -mediated gene disruption is a clinically relevant mechanism of antibiotic resistance in M. tuberculosis that should be considered for molecular diagnostics. Concomitantly, this analysis provides a list of 333 IS 6110 -disrupted genes in clinical tuberculosis isolates that can be deemed nonessential for human infection. IMPORTANCE To help control the spread of drug-resistant tuberculosis and to guide treatment choices, it is important that rapid and accurate molecular diagnostic tools are used. Current molecular diagnostic tools detect the most common antibiotic-resistance-conferring mutations in the form of single nucleotide changes, small deletions, or insertions. Mobile genetic elements, named IS 6110 , are also known to move within the M. tuberculosis genome and cause significant genetic variations, although the role of this variation in clinical drug resistance remains unclear. In this work, we show that both in vitro and in data analyzed from 6,426 clinical M. tuberculosis strains, IS 6110 elements are found that disrupt specific genes essential for the function of a number of pivotal antituberculosis drugs. By providing ample evidence of clinically relevant IS 6110 -mediated drug resistance, we believe that this shows that this form of genetic variation must not be overlooked in molecular diagnostics of drug resistance.