RESUMEN
Background: Rifampicin (RIF) is a key first-line drug used to treat tuberculosis, a primarily pulmonary disease caused by Mycobacterium tuberculosis. RIF resistance is caused by mutations in rpoB, at the cost of slower growth and reduced transcription efficiency. Antibiotic resistance to RIF is prevalent despite this fitness cost. Compensatory mutations in rpoABC genes have been shown to alleviate the fitness cost of rpoB:S450L, explaining how RIF resistant strains harbor this mutation can spread so rapidly. Unfortunately, the full set of RIF compensatory mutations is still unknown, particularly those compensating for rarer RIF resistance mutations. Objectives: We performed an association study on a globally representative set of 4,309 whole genome sequenced clinical M. tuberculosis isolates to identify novel putative compensatory mutations, determine the prevalence of known and previously reported putative compensatory mutations, and determine which RIF resistance markers associate with these compensatory mutations. Results and conclusions: Of the 1,079 RIF resistant isolates, 638 carried previously reported putative and high-probability compensatory mutations. Our strict criteria identified 46 additional mutations in rpoABC for which no strong prior evidence of their compensatory role exists. Of these, 35 have previously been reported. As such, our independent corroboration adds to the mounting evidence that these 35 also carry a compensatory role. The remaining 11 are novel putative compensatory markers, reported here for the first time. Six of these 11 novel putative compensatory mutations had two or more mutation events. Most compensatory mutations appear to be specifically compensating for the fitness loss due to rpoB:S450L. However, an outbreak of 22 closely related isolates each carried three rpoB mutations, the rare RIFR markers D435G and L452P and the putative compensatory mutation I1106T. This suggests compensation may require specific combinations of rpoABC mutations. Here, we report only mutations that met our very strict criteria. It is highly likely that many additional rpoABC mutations compensate for rare resistance-causing mutations and therefore did not carry the statistical power to be reported here. These findings aid in the identification of RIF resistant M. tuberculosis strains with restored fitness, which pose a greater risk of causing resistant outbreaks.
RESUMEN
Cross-resistance in rifamycins has been observed in rifampin (RIF)-resistant Mycobacterium tuberculosis complex isolates; some rpoB mutations do not confer broad in vitro rifamycin resistance. We examined 164 isolates, of which 102 were RIF-resistant, for differential resistance between RIF and rifabutin (RFB). A total of 42 unique single mutations or combinations of mutations were detected. The number of unique mutations identified exceeded that reported in any previous study. RFB and RIF MICs up to 8 µg/mL by MGIT 960 were studied; the cut-off values for susceptibility to RIF and RFB were 1 µg/mL and 0.5 µg/mL, respectively. We identified 31 isolates resistant to RIF but susceptible to RFB with the mutations D516V, D516F, 518 deletion, S522L, H526A, H526C, H526G, H526L, and two dual mutations (S522L + K527R and H526S + K527R). Clinical investigations using RFB to treat multidrug-resistant tuberculosis cases harboring those mutations are recommended.
Asunto(s)
Antibióticos Antituberculosos/farmacología , ARN Polimerasas Dirigidas por ADN/genética , Mutación Missense , Mycobacterium tuberculosis/efectos de los fármacos , Rifabutina/farmacología , Rifampin/farmacología , Tuberculosis/microbiología , Humanos , Pruebas de Sensibilidad Microbiana , Mycobacterium tuberculosis/enzimología , Mycobacterium tuberculosis/genética , Mycobacterium tuberculosis/aislamiento & purificaciónRESUMEN
Non-cystic fibrosis bronchiectasis (NCFB) is an increasingly prevalent disease that places a significant burden on patients and health systems globally. Although many of the therapies used to treat NCFB were originally developed as cystic fibrosis (CF) therapies, not all of them have been demonstrated to be efficacious in NCFB and some may even be harmful. This article explores the evidence for which therapeutic strategies used to treat CF have been translated into the care of NCFB. The conclusion is that therapies for adult NCFB cannot be simply extrapolated from CF clinical trials, and in some instances, doing so may actually result in harm.