Streptococcus porcorum sp. nov., isolated from domestic and wild pigs

Seven isolates of an unidentified Gram-stain-positive, catalase-negative, coccus-shaped organism isolated from domestic and wild pigs were characterized by phenotypic and molecular-genetic methods. Based on cellular morphology and biochemical criteria, the isolates were tentatively assigned to the genus Streptococcus, although the organisms did not appear to correspond to any recognized species. Comparative 16S rRNA gene sequencing showed that the unknown bacterium was phylogenetically closely related to, but distinct from, Streptococcus suis (97.5 % 16S rRNA gene sequence similarity to the type strain). rpoB and sodA sequence analysis showed minimum interspecies divergence from phylogenetically close 16S rRNA gene sequence-based relatives of 13.8 and 18.6 %, respectively. DNA-DNA hybridization of a strain of the unidentified organism demonstrated 8-18 % reassociation with S. suis NCTC 10234(T). The novel bacterium could be distinguished from S. suis and other Streptococcus species using biochemical tests. On the basis of phenotypic and phylogenetic evidence, it is proposed that the unknown isolates from domestic and wild animals be assigned to a novel species of the genus Streptococcus, Streptococcus porcorum sp. nov. The type strain is 682-03(T) (= CCUG 58479(T) = CECT 7593(T))

Genomic evidence for the evolution of Streptococcus equi : host restriction, increased virulence, and genetic exchange with human pathogens

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.Publisher PDFPeer reviewe