But, a similar procedure followed with different strains of S. pneumoniae failed to enhance replication of six IAV, including swine H3N2. As influenza and pneumococci commonly coinfect the upper respiratory tract of humans we decided to determine whether IAV titers change in the presence of pneumococcal products or with pretreatment of different live pneumococcal strains. For this analysis we made use of a range of IAV strains isolated originally from pigs and humans, belonging to subtypes H1N1, H1N2, and H3N2, including the pandemic 2009 H1N1 virus. As diversity within the pneumococcal population is substantial, the use of a single strain would restrict the conclusions that could be drawn. Therefore, we included 12 different strains of S. pneumoniae, eight of which are recent isolates from the human upper respiratory tract. Overall, our study represented the interplay of genetically variable IAV and pneumococci routinely found in the human population. Given that we saw no biologically relevant differences in IAV replication with any bacterial and viral combination, it seems Torin 1 distributor likely that the same outcome would be observed with most strains. We performed our initial studies using treatment of MDCK cells with pneumococcal products and confirmed that the treatment did not have any influence on IAV replication. Data from previous influenza virus pandemics and seasonal influenza outbreaks indicated that coinfections with S. pneumoniae and IAV cause increased disease severity. To investigate mechanisms of disease synergy due to these two organisms, several studies have shown that influenza virus induces susceptibility of host cells to S. pneumoniae infection. This occurs through induction of secretion of IFN-c by T cells and reduced secretion of chemokines, associated with activation of NF-kB in alveolar macrophages, mediated through influenza virus. However, until now knowledge on whether S. pneumoniae has any role in replication of IAV in vitro was unknown. Pneumococcal-influenza synergism was demonstrated in vivo in mice using rodent adapted strains. Influenza infection preceding pneumococcal challenge primed the development of bacterial pneumonia and led to 100% mortality. In a study when infant mice were colonized with S. pneumoniae and subsequently infected with IAV three days later, increased pneumococcal colonization and disease in the presence of IAV was noticed, associated with significantly reduced viral titers in nasopharynx compared to control mice. In yet another investigation, mice were infected with IAV followed by S. pneumoniae; viral titers initially increased and then declined slowly. Recently, it was demonstrated that S. pneumoniae enhances the human metapneumovirus infection in polarized bronchial epithelial cells in vitro. However, there is no direct evidence showing the influence of S. pneumoniae on the replication of IAV in vitro in epithelial cells. Our study using epithelial cell lines revealed the absence of any influence of live pneumococci preexposure on IAV replication, this is in contrast to the published in vivo results in rodents.