Abstract
Background Streptococcus pneumoniae (Spn) is typically an asymptomatic colonizer of the nasopharynx but it also causes pneumonia and disseminated disease affecting various host anatomical sites. Transition from colonization to invasive disease is not well understood. Studies have shown that such a transition can occur as result of influenza A virus coinfection.
Methods We investigated the pneumococcal (serotype 19F, strain EF3030) and host transcriptomes with and without influenza A virus (A/California/07 2009 pH1N1) infection at this transition. This was done using primary, differentiated Human Bronchial Epithelial Cells (nHBEC) in a transwell monolayer model at an Air-Liquid Interface (ALI), with multispecies deep RNA-seq.
Results Distinct pneumococcal gene expression profiles were observed in the presence and absence of influenza. Influenza coinfection allowed for significantly greater pneumococcal growth and triggered the differential expression of bacterial genes corresponding to multiple metabolic pathways; in totality suggesting a fundamentally altered bacterial metabolic state and greater nutrient availability when coinfecting with influenza. Surprisingly, nHBEC transcriptomes were only modestly perturbed by infection with EF3030 alone in comparison to that resulting from Influenza A infection or coinfection, which had drastic alterations in thousands of genes. Influenza infected host transcriptomes suggest significant loss of ciliary function in host nHBEC cells.
Conclusions Influenza A virus infection of nHBEC promotes pneumococcal infection. One reason for this is an altered metabolic state by the bacterium, presumably due to host components made available as result of viral infection. Influenza infection had a far greater impact on the host response than did bacterial infection alone, and this included down regulation of genes involved in expressing cilia. We conclude that influenza infection promotes a pneumococcal metabolic shift allowing for transition from colonization to disseminated disease.
Author summary Secondary Streptococcus pneumoniae bacterial infections typically occur after influenza A virus respiratory infection. Such coinfections often lead to invasive pneumococcal disease. The mechanisms involved in this process are not well understood. Here, using an ex vivo human lung bronchial epithelial cell model, we investigated the biological processes of the host and pneumococcus occurring at this niche, during coinfection with multi-species transcriptomics techniques, and in vivo mouse model experimentation. We observed stark differences in global pneumococcal metabolism in different infection states, as well as viral induced epithelial cell changes in ciliary function, potentially aiding pneumococcal dissemination. Overall, this study identified broad and targeted biological processes involved in this host-pathogen interaction.
Competing Interest Statement
The authors have declared no competing interest.
