Acute infection with influenza virus enhances susceptibility to fatal pneumonia following Streptococcus pneumoniae infection in mice with chronic pulmonary colonization with Pseudomonas aeruginosa.

We established a mouse model in which fatal pneumonia was induced by pneumococcal superinfection following influenza virus infection in chronic Pseudomonas aeruginosa infected mice. In this mouse model, influenza virus infection caused a significant increase in inflammatory cells, cytokines and severe tissue damage in the lungs of these P. aeruginosa infected mice, before pneumococcal infection. Intrapulmonary virus titres were significantly increased in mice with chronic P. aeruginosa infection, compared with control mice. Neutrophil function analysis showed significant reduction of myeloperoxidase (MPO) activity and lysozyme secretion by influenza virus infection in these mice. Our results suggest that influenza virus infection may play an important role in inducing pneumococcal pneumonia in chronic P. aeruginosa infected mice. Our results suggested that our mouse model is useful for investigating the pathogenesis of influenza virus infection in patients with chronic lung infection.