Abstract
Mycobacterium abscessus is an environmental non-tuberculous mycobacteria causing severelung infections in cystic fibrosis patients. Its intrinsic resistance to antibiotics renders treatmentsextremely challenging. This pathogen has developed a wide panel of strategies to resist to antibiotics,including efflux pumps and target-modifying enzymes. Standard antibiotherapy combines an-lactams (imipenem (IPM)) and macrolides (clarithromycin (CLR)or azithromycin (AZM)). My thesis was focusing on the regulation of antibiotic resistance mechanismsinvolving efflux pumps from the MmpL family as well as an enzyme modifying the macrolide target.Selection of resistant mutants against thiacetazone derivatives (TACd) and clofazimine (CFZ) unraveledmutations in the TetR regulators MAB_4384 and MAB_2299c, respectively. The CFZ-mutants, also coresistantto bedaquiline (BDQ), overexpress two distinct MmpS/MmpL, MAB_135c/1134c andMAB_2300/2301 while the TACd mutants overproduce the MAB_4383c/4382c efflux pump.Biochemical, genetic and structural approaches confirmed their involvement in drug resistancemechanisms. MAB_2299c could therefore represent a potential resistance marker to monitor in strainsisolated from patients under CFZ/BDQ therapy. The methyltransferase Erm(41) modifies the adenosine2058 of the ribosomal 23S rRNA, protecting the ribosome from the macrolides. WhiB7 may representa major actor in inducible resistance, observed in 40% of clinical cases, often leading to treatmentfailure. We confirmed the role of WhiB7 in this process and showed that inducible resistance occurredalso in vivo in the zebrafish model. Our data suggest that AZM is a stronger and faster resistanceinducer than CLR in vitro and that both drugs show antagonism with AMK, thus reducing drugs’efficacy. This work enriched our knowledge regarding both MmpL-mediated and macrolides inducibleresistance mechanism against M. abscessus. It also provides new efficient tools to investigate thefunction of proteins through a novel unmarked gene deletion approach and to rapidly assay newantibiotics to counteract inducible macrolide resistance.