Ribeiro GM, et al. - In order to better understand the successful survival strategies of Mycobacterium abscessus subsp. massiliense CRM0019, researchers determined its infectivity and proliferation in macrophages (RAW and BMDM) and alveolar epithelial cells (A549). Findings suggested that M. abscessus CRM0019 created a protective and replicative niche in alveolar epithelial cells mainly by avoiding phagosome maturation. CRM0019 recovered from infected macrophages remained infective and displayed greater intracellular growth in A549 cells compared to the ATCC 19977 strain. This evasion strategy in alveolar epithelial cells seemed to contribute to the long survival of the CRM0019 strain in the host and thus to the inefficacy of in vivo treatment.

Methods

• Researchers here assessed the following parameters for both M. abscessus CRM0019 as well as the reference strain M. abscessus ATCC 19977: internalization, intracellular survival for up 3 days, competence to subvert lysosome fusion and the intracellular survival after cell reinfection.

Results

• In this work, CRM0019 and ATCC 19977 strains indicated the same internalization rate (approximately 30% after 6 h infection), in both A549 and RAW cells.
• Colony forming units data in contrast indicated that CRM0019 survived better in A549 cells than the ATCC 19977 strain.
• In A549 cells, phagosomal characteristics of CRM0019 indicated the bacteria inside tight phagosomes, contrasting to the loosely phagosomal membrane in macrophages.
• In both cell types, this observation holds for the ATCC 19977 strain.
• Assessment of the competence to subvert lysosome fusion was performed by acidification and acquisition of lysosomal protein.
• In all cell lines, for M. abscessus strains the phagosomes were acidified; however, the acquisition of lysosomal protein was reduced by CRM0019 compared to the ATCC 19977 strain, in A549 cells.
• Conversely, in macrophages, both M. abscessus strains seemed located in mature phagosomes, however without bacterial death.
• Once recovered from macrophages, M. abscessus were able of establishing a new intracellular infection.
• Nevertheless, findings revealed that only CRM0019 had a higher growth rate in A549, increasing nearly 10-fold after 48 and 72 h.