Mycobacterium abscessus extracellular vesicles increase mycobacterial resistance to clarithromycin in vitro.

Nontuberculous Mycobacteria (NTM) are a group of emerging bacterial pathogens that have been identified in cystic fibrosis (CF) patients with microbial lung infections. The treatment of NTM infection in CF patients is challenging due to the natural resistance of NTM species to many antibiotics. Mycobacterium abscessus is one of the most common NTM species found in the airways of CF patients. In this study, we characterized the extracellular vesicles (EVs) released by drug-sensitive M. abscessus untreated or treated with clarithromycin (CLR), one of the frontline anti-NTM drugs. Our data show that exposure to CLR increases mycobacterial protein trafficking into EVs as well as the secretion of EVs in culture. Additionally, EVs released by CLR-treated M. abscessus increase M. abscessus resistance to CLR when compared to EVs from untreated M. abscessus. Proteomic analysis further indicates that EVs released by CLR-treated M. abscessus carry an increased level of 50S ribosomal subunits, the target of CLR. Taken together, our results suggest that EVs play an important role in M. abscessus resistance to CLR treatment.

Characterization of Exosomes Released from Mycobacterium abscessus-Infected Macrophages.

Extracellular vesicles (EVs), such as exosomes, play a critical role in cell-to-cell communication and regulating cellular processes in recipient cells. Non-tuberculous mycobacteria (NTM), such as Mycobacterium abscessus, are a group of environmental bacteria that can cause severe lung infections in populations with pre-existing lung conditions, such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). There is limited knowledge of the engagement of EVs in the host-pathogen interactions in the context of NTM infections. In this study, we found that M. abscessus infection increased the release of a subpopulation of exosomes (CD9, CD63, and/or CD81 positive) by mouse macrophages in cell culture. Proteomic analysis of these vesicles demonstrated that M. abscessus infection affects the enrichment of host proteins in exosomes released by macrophages. When compared to exosomes from uninfected macrophages, exosomes released by M. abscessus-infected macrophages significantly improved M. abscessus growth and downregulated the intracellular level of glutamine in recipient macrophages in cell culture. Increasing glutamine concentration in the medium rescued intracellular glutamine levels and M. abscessus killing in recipient macrophages that were treated with exosomes from M. abscessus-infected macrophages. Taken together, our results indicate that exosomes may serve as extracellular glutamine eliminators that interfere with glutamine-dependent M. abscessus killing in recipient macrophages.