Co infection of respiratory syncytial viruses (RSV) and streptococcus pneumonia modulates pathogenesis and dependent of serotype and phase variant.

Streptococcus pneumoniae (pneumococcus) is touted to be the generally found pathogen in patients with respiratory issues and there is an epidemiologic linkage present between Respiratory syncytial virus (RSV). This study aim at investigating the interaction between RSV and two serotypes of S. pneumoniae using a distinct animal model and a well-established colonizing pneumococcal strain. Phase variants phenotype of each strain was determined under oblique light. Co infection model was developed using BALB/c mice housed in a BSL-2 facility. Coinfection experiments were performed and number of bacterial colonies was quantified and phase determination was evaluated. RSV was detected in sample through real-time quantitative PCR. Adherence assays were performed to determine adherence of Spn strains and its knock out ΔNanA to nasopharyngeal carcinoma (NPC) epithelial CNE3 cell line. The biofilm viability was determined and phase composition was counted using plate count. Neuraminidase activity was measured in fluorometircassessed using 2'-(4-methylumbelliferyl)-α-D-N-acetylneuraminic acid (MUAN) as substrate as described in earlier literature. The GraphPad Software version 5.01 i.e., GraphPad Prism was used to conduct the statistical analysis. The extent of bacterial colonization was increased significantly (p < 0.05), when the mice were co infected. Nasal epithelium remained intact in mock sample with features of a thick mucociliary border. A small percentage of pneumococci exhibit phase variation between opaque phase and transparent phase. The percentage adherent of both phase were not found to be varying significantly within serotype but it was seen that nonpathogenic type 27 was more adherent. Biofilm formation was selectively more for transparent phase from a mixed-phase inoculum. Adherence of both phase variant of S. pneumoniae to nasopharyngeal epithelial cells 2 h post infection expressed as the percentage of adherent bacteria relative to the inoculum. In absence of viral infection, the nasal colonization of the opaque and the transparent variant was increased many folds, which was a significant differences. The extent of nasal colonization by the ΔNanA mutant strain were significantly reduced post-bacterial infection for both type of wild-type (P < 0.05). The findings explore insights into the interactions occurring between S. pneumoniae and RSV during respiratory infections and pneumococcal acquisition, indicate that pneumococcal serotypes have different ability to cause infection as well as co infections and potentially follow an unappreciated mechanism. Much more research work is needed to further understand the minutiae of this interaction within co-infection process.