Resistance of infant mice to <i>Streptococcus pneumoniae</i> infection induced by the immunization with recombinant chimeric pneumococcal protein PSPF (PsaA- Spr1875-PspA-FliC).

Swiss albino infant mice (3-week old) were immunized by nasal route with PSPF (20 μg in 25 μl of sterile PBS) on days 0, 14 and 28. Five days after the last immunization, mice were nasally infected with S. pneumoniae serotypes 3, 6B, 14, or 19F (107 CFU/mouse). Mice treated by the nasal route with sterile PBS were used as controls. Two days after pneumococcal challenge, lung and blood samples were obtained for the determination of S. pneumoniae cells counts. Each experimental group consisted of 3 mice per group and experiments were performed in triplicate (n = 9). Results were expressed as mean ± standard deviation. Differences were considered significant at p < 0.05 (*) when compared with non-immunized animals.