VIABLE MYCOBACTERIUM ABSCESSUS WITHIN PULMONARY AGGREGATE BIOFILMS IN A CHRONIC LUNG INFECTION MODEL

To better understand disease progression and test potential novel therapeutics, pre-clinical models of multidrug-resistant Mycobacterium abscessus (MAB) infection, which is increasingly prevalent in individuals with lung disease such as cystic fibrosis, are needed. We developed an acute (4-day) model of MAB-induced murine lung infection induced via a low intratracheal (IT) challenge dose. Here, we repeated the challenge regimen but extended the observation period and evaluation criteria to assess chronicity. 26 immunocompetent mice were challenged IT and followed for 28 days. Lungs were collected weekly to assess bacterial load and for histological assessment. BAL fluids were assessed for hemoptysis, cytokines, and immune cells. Live/Dead staining, vital imaging, and targeted RT-PCR were performed to assess duration of viable MAB infection. Auramine/Rhodamine staining indicated presence of MAB aggregate biofilms which increased in size from day 7 to 28 post-challenge. Histologically, pre-granulomas formed by day 7 and were maintained through day 28. We also observed increased levels of proinflammatory cytokines and sustained monocyte levels. Vital stain of lung homogenates demonstrated that MAB aggregate biofilms were viable, as evidenced by amplification of short-lived MAB-specific mRNA by RT-PCR. Via a widely available route of infection, MAB-induced pulmonary disease included formation of aggregate biofilms and granulomatous inflammation that developed over 28 days with multiple distinct markers of sustained infection in an immunocompetent mouse. These data support utility of this model for further studies of pathogenesis, treatment, and ideally, prevention strategies for chronic MAB-induced pulmonary infection.