Molecular Characterization of Streptococcus Pneumoniae in Children Living in Southwest China and Assessment of a Potential Protein Vaccine, RPfbA

Background: Few children living in southwest China are vaccinated against Streptococcus pneumoniae (S. pneumoniae), which is an important pathogen in causing high morbidity and high mortality. This study aimed the molecular characterization of S. pneumoniae strains isolated from children and a new vaccine strategy based on a potential protein antigen.

Methods: Molecular characterizations, including serotype, virulence gene and pilus analyses, were performed using PCR. Seven housekeeping genes were sequenced to identify the sequence types (STs), and antibiotic resistance was analysed using the microdilution broth method. In addition, we evaluated the protective effects of recombinant plasmin- and fibronectin-binding protein A (rPfbA) in murine pneumococcal infection models by challenge and passive transfer analyses, and assessed cytokine changes after immunization.

Results: The prevalent serotypes were 19F (31.4%), 19A (21.6%), 6B (13.7%), 14 (11.8%) and 23F (9.8%), and the coverage rates of the 13-valent pneumococcal conjugate vaccine (PCV13) were high in 93.3% of the isolates. The predominant STs were ST271 (23.5%), ST320 (21.6%) and ST876 (11.8%). Most of the S. pneumoniae isolates were resistant to erythromycin (95.1%) and clindamycin (90.2%). The molecular distributions and antibiotic resistance rates of the S. pneumoniae isolates differed between the plateau and the basin regions. More than 93% of the S. pneumoniae isolates carried ply, cbpA, phtD and nanA, and over half of the isolates carried pilus-1, pilus-2 and pfbA. Mucosal immunization with rPfbA induced pneumococcal specific antibody responses which provided to eliminate colonization in lung and nasopharynx, and protection against pneumococcal challenge.

Conclusion: Vaccine strategies based on epidemiological surveillance can be more adaptive to specific areas, reduce costs and protect against changing antigenic sites. We advise that children currently living in southwest China be vaccinated with PCV13.