Tobramycin enhances Mycobacterium abscessus fitness through whiB7 induction

Nontuberculous mycobacteria (NTM) are opportunistic pathogens that cause pulmonary disease (PD) in people with bronchiectasis and other chronic airway 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 cystic fibrosis (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 viability in the presence of hydrogen peroxide (H₂O₂), growth in human macrophages, and survival in mice. Deletion of whiB7 reduced Mabsc viability in the presence of H₂O₂, decreased Mabsc's ability to persist in macrophages, and disrupted tobramycin's ability 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 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.