Mycobacterium abscessus virulence traits unraveled by transcriptomic profiling in amoeba and macrophages

Abstract

Free-living amoebae are thought to represent an environmental niche in which amoebaresistant bacteria may evolve towards pathogenicity. To get more insights into factors playing a role for adaptation to intracellular life, we characterized the transcriptomic activities of the emerging pathogen Mycobacterium abscessus in amoeba and murine macrophages (Mφ) and compared them with the intra-Amoebal transcriptome of the closely related, but less pathogenic Mycobacterium chelonae. Data on up-regulated genes in amoeba point to proteins that allow M. abscessus to resist environmental stress and induce defense mechanisms, as well as showing a switch from carbohydrate carbon sources to fatty acid metabolism. For eleven of the most upregulated genes in amoeba and/or Mφ, we generated individual gene knock-out M. abscessus mutant strains, from which ten were found to be attenuated in amoeba and/or Mφ in subsequence virulence analyses. Moreover, transfer of two of these genes into the genome of M. chelonae increased the intra-Mφ survival of the recombinant strain. One knock-out mutant that had the gene encoding Eis N-Acetyl transferase protein (MAB_4532c) deleted, was particularly strongly attenuated in Mφ. Taken together, M. abscessus intra-Amoeba and intra-Mφ transcriptomes revealed the capacity of M. abscessus to adapt to an intracellular lifestyle, with amoeba largely contributing to the enhancement of M. abscessus intra-Mφ survival.