Strategies and Consequences of Polymicrobial Nasal Colonization

PROJECT SUMMARY The upper respiratory tract is colonized by a complex and dynamic community of commensal bacteria and opportunistic pathogens. As colonization is frequently a prerequisite for subsequent respiratory infection, this resident flora represents a critical reservoir for bacterial pathogens responsible for sinusitis, acute otitis media, and pneumonia. Among the leading agents of community-acquired pneumonia are Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Staphylococcus aureus, all of which are highly effective in colonizing the upper respiratory tract of asymptomatic individuals. Colonization of the respiratory tract is often polymicrobial with intense competition for limited nutritional resources, resulting in both synergistic and antagonistic interactions between or within species. While our understanding of the bacterial and host factors contributing to colonization of the upper respiratory tract has advanced considerably, a key aspect that remains unresolved is an understanding of how polymicrobial interactions within the respiratory tract impact a pathogen’s ability to colonize and cause infection. In my preliminary data, I demonstrate that S. pneumoniae undergoes extensive transcriptional reprogramming upon co-culture with other respiratory pathogens. In addition to identifying interactions between bacterial species, few models have determined the impact of interspecies competition on subsequent host responses to a particular pathogen. A key gap in advancing this field has been the lack of effective murine models of co-colonization, preventing detailed immunological and biological characterization. I have developed a novel murine co-colonization model that effectively recapitulates many of the published clinical observations. Furthermore, I demonstrate that in vivo co-colonization can dramatically impact whether protective capacity is generated following colonization, suggesting a critical link to host-mediated immunity. My overall goals are to 1) leverage functional genomics methods to determine how bacterial virulence networks are altered in the context of complex infectious colonization models, and 2) determine the effect of these colonization networks on cellular host responses following colonization through profiling of host mucosal responses. In Aim 1 I will utilize a functional genomics strategy to identify pathways utilized by Streptococcus pneumoniae that are operative during interspecies competition, which has not been attempted in the context of a polymicrobial colonization model. In Aim 2 I will identify key cell populations responsible for generating protection against subsequent infection by Streptococcus pneumoniae using flow cytometry and identify T-cell receptor (TCR) motifs unique to polymicrobial infections using a newly developed TCR repertoire sequencing strategy. Despite the several clinical observations made regarding the host immune response to co-infection, many of these observations have not been explored mechanistically. I hypothesize that distinct genetic determinants and host responses are operative during interspecies competitive models of colonization that impact subsequent infection susceptibility.