Streptococcus pneumoniae (the pneumococcus) is an effective colonizer of the human nasopharynx (NP) that on occasion causes disease. However, due to widespread colonization, disease occurs often enough that S. pneumoniae is a leading cause of numerous infections including otitis media (OM) in children, with associated complications, such as hearing loss and impairment of language and cognitive development. Although pneumococcal pathogenesis has been studied for a long time, our understanding of the complex interactions between the human host and bacteria, especially as they relate to colonization and the transition to OM is incomplete. Epidemiologically, transition from colonization to OM is associated with concomitant virus infection or other assaults on the host defense system, but the specific mechanisms involved are not very clear. We recently made the novel observation that pneumococcal NP carriage in vivo is associated with biofilm formation and have shown that recapitulation of this phenotype in vitro requires aspects of the NP environment, including lower temperature, interaction with epithelial cells and limited nutrient availability. Moreover, we have discovered that perturbation of this environment specifically releases bacteria from the biofilm that readily disseminate to the middle ear (ME), causing more severe disease than either biofilm bacteria or bacteria grown in broth and have a unique gene expression profile, that has allowed us to identify several molecules required for bacterial release, dissemination, and induction of OM. The goals of these studies are to mechanistically explore the signals involved in pneumococcal release from NP biofilms (both pneumococcal biofilms and poly-microbial biofilms with common NP colonizing species), dissemination to, and survival in the ME using our novel epithelial cell-based biofilm models and animal models of colonization and infection, and we hypothesize that perturbing the NP environment with dispersants such as increased temperature (fever), nutrients and ATP (associated with cell damage) and virus infection (common disease trigger), that is highly associated with pneumococcal OM will induce release of biofilm bacteria with altered phenotypes associated with increased ability to cause infection of the ME. In the studies delineated herein, we will explore release of bacteria from biofilms in vitro and in vivo after exposure to physiological changes of the normal biofilm/NP environment (Aim 1) or to influenza A virus and respiratory syncytial virus infection (Aim 2). We will then study the ability of bacteria released in vitro or in vivo to induce OM. Finally, we will expand our transcriptome analyses of the bacterial populations using RNA-seq and identify and characterize molecules involved in bacterial biofilm release, dissemination to, and induction of OM (Aim 3). The studies will provide mechanistic information regarding the release of virulent bacteria from biofilms growing in vitro and in vivo and provide specific information of the environmental and bacterial factors responsible for virulence induction in vivo that can be used to inhibit the transition to otitis media.
We have recently observed that the prominent middle ear pathogen Streptococcus pneumoniae (the pneumococcus) colonizes the nasopharynx as biofilms and have developed methodology to study the signals responsible for transition from colonization to otitis media in vivo and in vitro. The aim of this application is to mechanisticall understand how pneumococci in nasopharyngeal biofilm are released to disseminate and induce otitis media by changing the nasopharyngeal environment by physiological assaults or virus infection. Understanding the key mechanism(s) and the phenotypes of the bacteria that cause infection will improve our understanding of both, pneumococcal physiology and pathogenesis as well as potentially help us identifying better vaccine and anti-microbial drug targets.
