Patterns of Global Genetic Diversity of Streptococcus pneumoniae Inferred Based on Archived Multilocus Sequence Typing Data

Streptococcus pneumoniae is the major cause of invasive pneumococcal disease (IPD). Since 1998, multilocus sequence typing (MLST) has been used for identifying the genotypes of strains of S. pneumoniae and helped reveal a diversity of local and regional epidemiological patterns for IPD, resulting in an archived MLST dataset of over 74,000 isolates. However, the global patterns of MLST sequence type (ST) and allele type (AT) distributions remain largely unexplored. In this study, we investigated the spatial and temporal patterns of AT and ST distributions of S. pneumoniae. We extracted S. pneumoniae MLST data from PubMLST.org and conducted various population genetic and phylogenetic analyses. Our analyses demonstrated both shared and unique distributions of STs and ATs among continental and national/regional populations. Among the 17915 STs in the dataset, 36 STs representing 15263 isolates were broadly shared among all six continents, consistent with recent gene flow and clonal dispersal of this pathogen. The analysis of molecular variance revealed that >96% genetic variations were found within individual continental and national/regional populations. However, though low (<4%), statistically significant genetic differentiation among continental and national populations were observed. Comparisons between non-clone-corrected and clone-corrected datasets showed that localized clonal expansion contributed significantly to the observed genetic differentiations among continents and countries/regions. Temporal analyses of the isolates showed that implementation of pneumococcal conjugate vaccine impacted the distributions of STs. Linkage disequilibrium analyses identified evidence for non-random recombination in all continental populations of this species. We discussed the implications of our analyses to the global epidemiology and future vaccine developments for S. pneumoniae.