Genetic diversity and antigenicity analysis of Streptococcus pneumoniae pneumolysin isolated from children with pneumococcal infection.

Background: Pneumolysin (Ply), as a major virulence factor of Streptococcus pneumoniae, has attracted increased attention for its potential value in the development of next-generation protein-based pneumococcal vaccines. This study aimed to analyze the genetic and antigenic diversity that can influence the immunogenicity of vaccines.
Methods: A total of 96 pneumococcal isolate samples were obtained from children of 1-35 months old with invasive pneumococcal diseases in Shanghai Children's Medical Center (Shanghai, China). After DNA amplification by PCR and Sanger sequencing, Ply DNA sequences were analyzed by bioinformatics tools, including ClustalX, BioEdit and MEGA7.
Results: Two alleles, allele 1 and 2, and 10 subtypes, of which were 6 novel subtypes, were identified. Nucleotide and amino acid sequence identity among these pneumococcal isolates were >99%. Subtypes with the same amino acid sequence were more closely evolutionarily related in the phylogenetic tree. Only minor differences in the B-cell epitopes were identified in the antigenicity plots of alleles 1 and 2. The most common serotype was serotype 19A.
Conclusions: The sequence diversity of Ply is limited although some allelic variations are detected. Different alleles exhibit similar antigenic patterns. Development of Ply-based vaccines may be a promising method to combat pneumococcal infection in the future.
(Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)