PsrP, a Protective Pneumococcal Antigen, Is Highly Prevalent in Children with Pneumonia and Is Strongly Associated with Clonal Type

Invasive pneumococcal disease (IPD) is a major health problem worldwide. Due to ongoing serotype replacement, current efforts are focused in an attempt to identify the pneumococcal antigens that could be used in a next-generation multivalent protein vaccine. The objective of our study was to use real-time PCR to determine the distribution and clonal type variability of PsrP, a protective pneumococcal antigen, among pneumococcal isolates from children with IPD or healthy nasopharyngeal carriers. psrP was detected in 52.4% of the 441 strains tested. While no differences were determined when the prevalence of psrP in colonizing strains (n = 89) versus that in all invasive strains (n = 352) was compared, a strong trend was observed when the prevalence of psrP in all pneumonia isolates (n = 209) and colonizing isolates (P = 0.067) was compared, and a significant difference was observed when the prevalence in all pneumonia isolates and those causing bacteremia (n = 76) was compared (P = 0.001). An age-dependent distribution of psrP was also observed, with the incidence of psrP being the greatest in strains isolated from children >2 years of age (P = 0.02). Strikingly, the presence of psrP within a serotype was highly dependent on the clonotype, with all isolates of invasive clones such as clonal complex 306 carrying psrP (n = 88), whereas for sequence type 304, only 1 of 19 isolates carried psrP; moreover, this was inversely correlated with antibiotic susceptibility. This finding suggests that inclusion of psrP in a vaccine formulation would not target resistant strains. We conclude that psrP is highly prevalent in strains that cause IPD but is most prevalent in strains isolated from older children with pneumonia. These data support the potential use of PsrP as one component in a multivalent protein-based vaccine.