Tobramycin enhances Mycobacterium abscessus fitness through whiB7 induction

Abstract

Nontuberculous mycobacteria (NTM) are opportunistic pathogens that cause pulmonary disease (PD) in people with bronchiectasis and other chronic airways diseases. Difficulty treating and eradicating NTM-PD highlights the need for improved understanding of bacterial mechanisms to establish chronic infections. People with the genetic disorder cystic fibrosis (CF) develop bronchiectasis and are the population at highest risk of NTM-PD, caused mainly by Mycobacterium avium or Mycobacterium abscessus (Mabsc). The majority of people with CF (pwCF) and bronchiectasis develop chronic Pseudomonas aeruginosa airway infections. We hypothesized that antibiotics used to treat P. aeruginosa infections could enhance Mabsc persistence in the CF airway. Here we demonstrate that clinically relevant concentrations of tobramycin, which does not kill Mabsc but is frequently administered to pwCF with chronic P. aeruginosa infections, induced Mabsc expression of whiB7, a transcription factor that activates genes associated with resistance to host defenses. Tobramycin promoted Mabsc resistance to killing by hydrogen peroxide (H2O2) and survival in both human macrophages and mice. Deletion of whiB7 increased Mabsc susceptibility to killing by H2O2, decreased ability of Mabsc to persist in macrophages, and disrupted ability of tobramycin to enhance Mabsc survival. Transcriptomic data defining the tobramycin associated WhiB7 regulon revealed differential gene expression of factors that could enhance Mabsc resistance to stress conditions such as those in found in the CF lung. Overall, our data indicate that administration of tobramycin to pwCF may have unexpected off-target effects, enhancing Mabsc whiB7 expression and promoting Mabsc persistent infection. Significance StatementPulmonary infections caused by Mycobacterium abscessus (Mabsc) are increasing in prevalence, especially in people with cystic fibrosis (pwCF) and bronchiectasis, and are very challenging to treat. Risk factors that predispose to Mabsc pulmonary infections remain poorly defined. This study demonstrates that tobramycin, an antibiotic commonly used to treat chronic Pseudomonas aeruginosa infections in pwCF, promotes Mabsc persistence by inducing Mabsc expression of the transcription factor whiB7. WhiB7 enhances Mabsc resistance to oxidative stress and survival in host macrophages. Transcriptome analysis reveals that tobramycin activates a large WhiB7 dependent regulon linked to stress tolerance and immune evasion. These findings highlight a clinically relevant off-target effect of tobramycin that may contribute to Mabsc persistence in polymicrobial infections.