- Targeting Pneumococcal Transmission The long-term goal of this project is a more comprehensive prevention of disease caused by Streptococcus pneumoniae (Spn, the pneumococcus). Our approach to the ongoing problem of the pneumococcus is based on the lessons from 19 years of widespread childhood immunization, which point to the critical need to interrupt host-to-host transmission if the incidence of Spn disease is to be reduced further. This key step in the Spn lifecycle, however, has not been the focus of previous investigation or vaccine discovery. This is because bacterial factors contributing to Spn contagion are poorly understood due to the complexities of studying natural transmission and a lack of tractable animal models. Our overall premise is that specific Spn genes contribute to its transmission and that their gene products are potential novel targets for prevention. We recently developed an infant mouse model of intra-litter spread that allows for the detailed study of the biology of Spn transmission. This model was used to establish the role of the toxin, pneumolysin, in mucosal inflammation that increases secretions that promote Spn shedding and facilitate its transmission. More recently, this model has been used to screen a genomic library of Tn-seq mutants to identify the complete set of `transmission' genes from a single isolate. Many of the `hits' encode enzymes that could function in binding to and degrading mucin glycoproteins. These products to be characterized in Aim#1 could allow Spn to exit the colonized host using mucus flow, then release itself from mucus entrapment to establish in a new host.
Aim#2 will take a separate approach by identifying Spn genes affecting natural transmission among strains circulating within a community. This will be carried out with a genome-wide association study (GWAS) on 3085 publicly-available whole genome sequences obtained from monthly nasal swabs of ~600 infants (Maela cohort). Candidate genetic elements will then be tested/confirmed in the infant mouse model of transmission. Our preliminary data using the infant mouse model recapitulates the experience from pneumococcal immunization in that humoral immunity to Spn blocks transmission. The focus of Aim#3 is early-stage vaccine testing. We will use the infant mouse model to determine the potential for conserved surface factors, including those identified in the Tn-seq and GWAS screens, to induce immunity that interrupts host-to-host spread without the requirement for within-host protection. At the conclusion of the project, we will understand how Spn promotes its transmission and whether transmission can be targeted to mitigate the continued high burden of pneumococcal disease.
This project aims to understand how the leading pathogen Streptococcus pneumoniae is transmitted from host-to-host. We will identify bacterial genes that contribute to transmission in an animal model as well as in natural transmission. The bacterial products we identify will then be tested as novel vaccine antigens to block transmission ? a critical step for the success of the organism.