(513) Unravelling the pathogenicity of Mycobacterium abscessus clinical isolates in CF pulmonary epithelial cell and mouse models of respiratory infection

Background: Mycobacterium abscessus (MA) infections in Cystic fibrosis (CF) patients display heterogeneous clinical outcomes. To date, the contribution to MA pulmonary disease (MA-PD) development by dominant circulating clones (DCCs) or morphotypes, remains to be elucidated. We aim at defining pathogenicity of CF MA clinical strains in CF pulmonary epithelial cell and mouse models of MA respiratory infection.

Methods: We collected eleven longitudinal MA strains isolated from five patients both at the early asymptomatic and MA-PD phase. We performed morphotype (rough and smooth phenotype) and whole genome sequencing (WGS) analysis. Moreover, we studied the host response induced by CF isolates in CF epithelial cells (CFF-16HBEgeCFTRΔF508) by host RNA sequencing and cytokines release. We also tested the virulence of MA clinicals strains in mouse models of acute and chronic lung infection.

Results: Epithelial cells infected with DCC1 strains displayed a higher pro-inflammatory response than DCC2 strains. Moreover, we found out that morphotype (smooth vs rough strains) is the main bacterial feature driving over 3000 host differentially expressed genes. This was confirmed also by the evaluation of IL6 and IL8 protein levels upon infection. Then, we tested the in vivo pathogenicity of two longitudinal strains from the same patient, belonging to DCC1 and displaying a different morphotype. Longitudinal persisted DDC1 rough strain displayed a higher bacterial burden and pro-inflammatory response, such as airway monocyte recruitment, than DDC1 smooth strain after 4 days post challenge in acute infection mouse model. We also exploited a mouse model of MA chronic lung infection. Here, we confirmed that DDC1 rough strain were able to persist with a higher bacterial load within murine lungs than DDC1 smooth strain after 14 days post infection.

Conclusions: Our findings suggest that rough DCC1 strains persisted within CF lung may cause more severe respiratory infections.

Acknowledgements: Supported by Italian CF foundation FFC#23_2020

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