The study shows that different strains of the bacteria Mycobacterium abscessus survive differently inside human cells. One especially aggressive strain from a sputum sample can avoid being killed by the natural antimicrobial peptide LL‑37 and triggers strong inflammation. This means not all M. abscessus are the same, and some can better dodge our innate defenses.

Mycobacterium abscessus subsp. abscessus (MABS) is an emerging, opportunistic pathogen found globally in freshwater biofilms and soil. Typically, isolates are treated as a uniform group of organisms and very little is known about their comparative survival in healthy host cells. We posit that environmentally- and clinically derived isolates, show differential infectivity in immune cells and resistance to innate defenses. Six MABS isolates were tested including three water biofilm/soil and three sputum-derived isolates. A clinical MABS type strain and an environmental isolate of Arthrobacter were also included. MABS counts were significantly higher compared to Arthrobacter after co-culture with Acanthamoeba lenticulata, BEAS-2B epithelial cells, alveolar macrophages and the THP-1 macrophage cell line. A rough sputum-derived MABS isolate emerged as an isolate with higher virulence compared to others tested, as both a pellicle and cord former, survivor in the human cell models tested, inducer of high and prolonged production of pro-inflammatory cytokines, and the capacity to evade LL-37. Findings support intraspecies variation between MABS isolates. These data indicate subversion of host immune defenses by environmental and clinical MABS isolates is nuanced and maybe isolate dependent, providing new information regarding the pathogenesis of NTM infections.