RESUMO
The continued evolution of bacterial pathogens has major implications for both human and animal disease, but the exchange of genetic material between host-restricted pathogens is rarely considered. Streptococcus equi subspecies equi (S. equi) is a host-restricted pathogen of horses that has evolved from the zoonotic pathogen Streptococcus equi subspecies zooepidemicus (S. zooepidemicus). These pathogens share approximately 80% genome sequence identity with the important human pathogen Streptococcus pyogenes. We sequenced and compared the genomes of S. equi 4047 and S. zooepidemicus H70 and screened S. equi and S. zooepidemicus strains from around the world to uncover evidence of the genetic events that have shaped the evolution of the S. equi genome and led to its emergence as a host-restricted pathogen. Our analysis provides evidence of functional loss due to mutation and deletion, coupled with pathogenic specialization through the acquisition of bacteriophage encoding a phospholipase A(2) toxin, and four superantigens, and an integrative conjugative element carrying a novel iron acquisition system with similarity to the high pathogenicity island of Yersinia pestis. We also highlight that S. equi, S. zooepidemicus, and S. pyogenes share a common phage pool that enhances cross-species pathogen evolution. We conclude that the complex interplay of functional loss, pathogenic specialization, and genetic exchange between S. equi, S. zooepidemicus, and S. pyogenes continues to influence the evolution of these important streptococci.
Assuntos
Evolução Molecular , Genes Bacterianos , Streptococcus equi/genética , Streptococcus equi/patogenicidade , Animais , Bacteriófagos/genética , Genoma , Cavalos , Humanos , Dados de Sequência Molecular , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Streptococcus equi/virologia , Streptococcus pyogenes/genética , VirulênciaRESUMO
Streptococcus pneumoniae is a human commensal and pathogen able to cause a variety of diseases that annually result in over a million deaths worldwide. The S. pneumoniae(Spain23F) sequence type 81 lineage was among the first recognized pandemic clones and was responsible for almost 40% of penicillin-resistant pneumococcal infections in the United States in the late 1990s. Analysis of the chromosome sequence of a representative strain, and comparison with other available genomes, indicates roles for integrative and conjugative elements in the evolution of pneumococci and, more particularly, the emergence of the multidrug-resistant Spain 23F ST81 lineage. A number of recently acquired loci within the chromosome appear to encode proteins involved in the production of, or immunity to, antimicrobial compounds, which may contribute to the proficiency of this strain at nasopharyngeal colonization. However, further sequencing of other pandemic clones will be required to establish whether there are any general attributes shared by these strains that are responsible for their international success.