A mobile ESX type VII secretion system enhances intracellular persistence in globally distributed Mycobacterium abscessus

Abstract Mycobacterium abscessus are non-tuberculous mycobacteria that are widespread in the environment and of increasing global clinical significance. Accumulating evidence shows that M. abscessus has emerged as an important pathogen, driven by highly drug-resistant lineages, enhanced transmissibility and the acquisition of specific virulence factors. In this study, we describe a previously uncharacterised ESX secretion system encoded on a 123-kbp plasmid identified in a clinical isolate of M. abscessus. This ESX system, termed ESX-pMA07, is distinct from ESX systems previously reported in M. abscessus in both sequence composition and locus organisation, characterised by a unique arrangement of core ESX components and low sequence identity to ESX-3, ESX-4 and plasmid-borne ESX-P systems. ESX-pMA07 was detected in geographically diverse clinical isolates but was restricted to particular genotypes within the global M. abscessus phylogeny. Transcriptional profiling revealed expression of ESX-pMA07 components in artificial cystic fibrosis media and during intracellular growth in macrophage cell lines. Using CRISPR interference, we show that inducible silencing of eccC, encoding the ATPase component of ESX-pMA07, significantly reduced intracellular survival of M. abscessus within macrophages. To our knowledge, this is the first characterisation of a functional, plasmid-borne ESX secretion system in M. abscessus, demonstrating that mobile genetic elements contribute to the pathogen’s intracellular persistence and may influence its evolving virulence. Author Summary Mycobacterium abscessus is a rapidly emerging, highly drug-resistant bacterium that causes chronic infections, particularly in people with underlying lung disease such as cystic fibrosis. The factors that enable certain M. abscessus strains to persist inside host cells are not fully understood. In this study, we identified a previously unrecognised type VII secretion system (ESX) encoded on a large plasmid in a clinical isolate of M. abscessus. This plasmid-borne ESX system, which we termed ESX-pMA07, is genetically distinct from the ESX systems normally found on the chromosome and was detected in geographically diverse clinical isolates, but restricted to specific lineages within the global M. abscessus population. We show that ESX-pMA07 genes are expressed under conditions relevant to lung infection and during intracellular growth in macrophages. Using inducible CRISPR interference to silence the ESX ATPase gene eccC, we demonstrate that ESX-pMA07 contributes to intracellular survival of M. abscessus in macrophages. These findings reveal that mobile genetic elements can encode functional secretion systems that enhance intracellular persistence, providing a mechanism for the emergence and spread of virulence traits in this important pathogen. Competing Interest Statement The authors have declared no competing interest.