Preclinical model of Mycobacteroides abscessus lung disease by nose-only exposure of mice to bacterial powder aerosol

The limitations of existing mouse models of lung infection with Mycobacteroides abscessus impede drug discovery and development. In contrast to current animal models that introduce NTM intravenously or by intranasal/intra-tracheal instillation or via bronchoscopy-guided insufflation, we developed a dry powder inhalation (DPI) of M. abscessus ATCC 19977 that generated paucibacillary lung infection and histopathology in immunocompetent mice. Swiss outbred mice receiving ∼1000 (3-log) colony forming units (CFU) of M. abscessus/gram lung tissue via the DPI administered by nose-only inhalation for 90 s showed peak bacterial burden of ∼3.35-log CFU/g in the lungs after 28 days. This was maintained at ∼2-log/g from Day 35 through 56 in the lungs, but not in the spleen. Histopathology indicated increasing severity of inflammation, fibrosis and lung consolidation. Bacteria were rarely recovered from spleen, and histopathological examination indicated partial resolution in the spleen between Days 49-56. The DPI, prepared by freeze-drying log-phase liquid culture with cryoprotectants was formulated to possess aerosol characteristics suitable for alveolar deposition. Aerosol exposure to inoculum mimics natural airborne infection. Non-invasive aerosol infection is convenient, inexpensive, does not require special equipment or extensive training and mitigates stress to animals, but biosafety level 3 containment is recommended to mitigate risk to experimenters.