Objective   To screen different formats of dominant antigens of DNA vaccine of Streptococcus pneumoniae.    Methods   The fragments of pneumococcal surface protein A (PspA’) and PBD [mutant of pneumococcal lysozyme (Ply)] from Streptococcus pneumoniae R6 genome were amplified and then cloned into the eukaryotic expression vector pcDNA3.1(+). These recombinant vectors pcDNA3.1-PspA’

pcDNA3.1-PBD and pcDNA3.1-PsaA (pneumococcal surface adhesin A

produced in our preliminary work) were transfected into BHK-21 cells

and their expressions were detected with Western blotting. In 7 d after receiving an injection of cardiotoxin into the quadriceps muscle of thigh

  BALB/c mice groups (Group A: pcDNA3.1(+); Group B: pcDNA3.1-PsaA+pcDNA3.1-PspA’; Group C: pcDNA3.1-PsaA’+pcDNA3.1-PBD; Group D: pcDNA 3.1-PspA+pcDNA3.1-PBD; Group E: pcDNA3.1-PsaA+pcDNA3.1-PspA’+pcDNA3.1-PBD; and PBS group) were injected intramuscularly by corresponding formats of recombinant vectors on Day 0 and 28 respectively. The serum levels of antibodies against PspA’

PsaA and PBD proteins were tested by ELISA on 28 d after last immunization. The nasopharyngeal colony count of Streptococcus pneumoniae D39 and survival time after intraperitoneal infection in BALB/c mice models were analyzed.    Results   The mice in Group B and Group E (P0.05) produced higher levels of serum IgGs in responses to PsaA and PspA’ than the other groups (P0.01vs Group A). The results of nasopharyngeal colony counting showed there was no significant difference between Group B and Group E

and they had significantly fewer pneumococci in the nasophary than the other 3 groups (P0.01 vs Group A). The same results were noted in the intraperitoneal infection of Streptococcus pneumoniae D39 in BALB/c mice models.    Conclusion   Among the formats of dominant candidate antigens for DNA vaccine

the DNA vaccine of the combined format of PspA’ and PsaA has higher performance in the protection from Streptococcus pneumoniae.