Phylogenetic distribution and longitudinal persistence of plasmids in Mycobacterium abscessus.

Mycobacterium abscessus, a non-tuberculous mycobacterium, is a cause of severe respiratory infections, notably in individuals with underlying lung conditions. Its high levels of intrinsic and acquired antimicrobial resistance make it particularly difficult to treat and horizontally acquired genetic elements may facilitate the spread of resistance. A small number of plasmids have been identified in this species, but their distribution, transmission dynamics across subspecies and clonal lineages remain poorly characterized. We analysed short-read genomic data from 3,060 M. abscessus isolates, including longitudinal samples, to characterize plasmid diversity and dynamics. Using a graph-based pan-genome approach, we identified 28 plasmids, including 15 previously unreported plasmids, mapped their distribution onto the species phylogeny and assessed their functional potential. Overall, 23.1% of isolates carried at least one plasmid, with higher prevalence in dominant circulating clones (DCCs) compared with non-DCCs. Plasmid carriage varied across subspecies and clonal backgrounds, and plasmids encoded numerous genes which may be linked to bacterial adaptation. Several plasmids persisted across multiple time points within individual patients, suggesting they can be highly stable over the course of a chronic infection.