Physicochemical and antigenic properties correlation in Streptococcus gordonii vaccine vectors and development of a Streptococcus pneumoniae intra-tracheal mouse model of pneumonia

In the present thesis, the correlation between the physicochemical and antigenic properties of different recombinant Streptococcus gordonii vaccine vectors was studied. Evaluation of vaccine efficacy, antigenicity and immugenicity is a crucial step in developing vaccines, thus investigating a simple method to analyze vaccine efficacy besides other methods could be a major part of developing bacterial vaccine vectors. To approach this, isoelectric point measurements and zeta-potential titration as well as antigenicity and immunogenicity of S.gordonii vaccine vectors (with fbpA, RPS, gtfg genes mutations expressing H1 antigen) were used. These data showed that strains with more positive surface charge had higher heterologous antigen recognition and lower antibody responses in the serum of immunized mice. This correlation between surface charge and antigenicity and immunogenicity revealed the importance of using simple methods such as zeta potential titration and isoelectric point measurements to predict engineered vaccine vectors antigenicity and possible efficacy. In the second part of the thesis the immune recall in the days following Streptococcus pneumoniae lung infection by transcriptomic analysis was studied. S. pneumoniae is the most common bacterial cause of community-acquired pneumonia. Host-pathogen interaction is poorly understood, and factors that drive a more severe phenotype are unknown. One way to study host response to pathogen is using the stimulation of immune system cells with live or killed bacteria. We combined transcriptomic and cytokine level analysis on stimulated mouse splenocytes revealing the presence of a recall immune response involving both innate and adaptive immunity, stronger from the fourth day after infection. This model could analyze immune responses involved in pneumococcal infection as well as vaccine and experimental therapies efficacy in future studies. Finally, the development of a S. pneumoniae mouse model of pneumonia by intra-tracheal infection was set up. The nasopharynx of humans is the only natural reservoir for the pneumococci. To mimic human pneumonia, mice models are widely used. Bacteria can be administered to mice intranasally, intratracheally or as aerosols. Pneumococcal pneumonia was induced in mice by intra-tracheal inoculation with different doses of S. pneumoniae TIGR4. Data showed high colonization of bacteria in lung, liver and spleen starting 24 hours post-infection. Pneumonia mortalities were observed in all mice infected by 108 within 24 hours of infection. Further analysis should be done to investigate the host-pathogen interaction as well as vaccine and experimental therapies efficacy by using this model.