Abstract
Influenza A virus (IAV) and Streptococcus pneumoniae (pneumococcus) are two major upper respiratory tract pathogens responsible for exacerbated disease in coinfected individuals. Despite several studies showing increased susceptibility to secondary bacterial infections following IAV infection, information on the direct effect of S. pneumoniae on IAV in vitro is unknown. This is an important area of investigation as S. pneumoniae is a common commensal of the human upper respiratory tract, present as an important coinfecting pathogen with IAV infection. A recent study showed that S. pneumoniae enhances human metapneumovirus infection in polarized bronchial epithelial cells in vitro. The aim of the current study was to determine whether treatment of epithelial cells with S. pneumoniae affects IAV replication using a standard immunofluorescence assay (IFA). For this study we used four IAV permissive epithelial cell lines including two human-derived cell lines, 12 pneumococcal strains including recent human clinical isolates which represent different genetic backgrounds and serotypes, and six IAV strains of varying genetic nature and pathogenic potential including the pandemic 2009 H1N1 virus. Our results suggested that pretreatment of MDCK cells with 7.5×106 colony-forming units (CFUs) of live S. pneumoniae resulted in gradual cell-death in a time-dependent manner (0.5 to 4 hr). But, pretreatment of cell lines with 7.5×105 and lower CFUs of S. pneumoniae had no detectable effect on either the morphology of cells or on the IAV replication. However, unlike in epithelial cell lines, due to influence of secreted host factors the effect of pneumococci on IAV replication may be different during coinfections in vivo in the human upper respiratory tract, and in vitro with primary human polarized bronchial epithelial cells.
Highlights
Influenza A virus (IAV) causes greater than 250,000 deaths annually in the industrialized world [1], and bacterial infections frequently cause secondary illnesses during influenza outbreaks [2,3]
Despite several studies showing increased susceptibility to secondary bacterial infection following IAV infection [6,7], other studies have shown that pretreatment of S. pneumoniae or its lysates led to induction of interferons, cytokines and chemokines which mitigate disease severity of IAV infection [5]
A calibration curve for each S. pneumoniae strain was drawn to determine the concentration of the bacteria in colony-forming units (CFUs) per mL corresponding to an absorbance measurement at OD600 (Figure 1, B)
Summary
Influenza A virus (IAV) causes greater than 250,000 deaths annually in the industrialized world [1], and bacterial infections frequently cause secondary illnesses during influenza outbreaks [2,3]. The IAV pandemics of the 20th century (1918, 1957, and 1968) clearly demonstrated that infection with IAV facilitates the progression of S. pneumoniae from a commensal organism to a potentially fatal pathogen [2,4]. Despite several studies showing increased susceptibility to secondary bacterial infection following IAV infection [6,7], other studies have shown that pretreatment of S. pneumoniae or its lysates led to induction of interferons, cytokines and chemokines which mitigate disease severity of IAV infection [5]. Due to lack of colonization of all the pathogenic strains of S. pneumoniae and infection of IAV strains in rodent models, in this study in vitro analysis was chosen instead of in vivo. The aim of the current study was to determine whether pretreatment of epithelial cells with S. pneumoniae affects IAV infection in different IAV permissive cell types
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
