title: Complex Population Structure and Virulence Differences among Serotype 2 Streptococcus suis Strains Belonging to Sequence Type 28.
abstract: Streptococcus suis is a major swine pathogen and a zoonotic agent. Serotype 2 strains are the most frequently associated with disease. However, not all serotype 2 lineages are considered virulent. Indeed, sequence type (ST) 28 serotype 2 S. suis strains have been described as a homogeneous group of low virulence. However, ST28 strains are often isolated from diseased swine in some countries, and at least four human ST28 cases have been reported. Here, we used whole-genome sequencing and animal infection models to test the hypothesis that the ST28 lineage comprises strains of different genetic backgrounds and different virulence. We used 50 S. suis ST28 strains isolated in Canada, the United States and Japan from diseased pigs, and one ST28 strain from a human case isolated in Thailand. We report a complex population structure among the 51 ST28 strains. Diversity resulted from variable gene content, recombination events and numerous genome-wide polymorphisms not attributable to recombination. Phylogenetic analysis using core genome single-nucleotide polymorphisms revealed four discrete clades with strong geographic structure, and a fifth clade formed by US, Thai and Japanese strains. When tested in experimental animal models, strains from this latter clade were significantly more virulent than a Canadian ST28 reference strain, and a closely related Canadian strain. Our results highlight the limitations of MLST for both phylogenetic analysis and virulence prediction and raise concerns about the possible emergence of ST28 strains in human clinical cases.
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada.
authors.forename: Taryn B T
authors.initials: TB
authors.lastname: Athey
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de Médecine Vétérinaire, Université de Montréal, St-Hyacinthe, Quebec, Canada.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Auger
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Teatero
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de Médecine Vétérinaire, Université de Montréal, St-Hyacinthe, Quebec, Canada.
authors.forename: Audrey
authors.initials: A
authors.lastname: Dumesnil
authors.affiliation: Bacterial and Parasitic Diseases Research Division, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Japan; The United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takamatsu
authors.affiliation: Department of Human Genetics, McGill University and Génome Québec Innovation Centre, Montreal, Quebec, Canada.
authors.forename: Jessica
authors.initials: J
authors.lastname: Wasserscheid
authors.affiliation: Department of Human Genetics, McGill University and Génome Québec Innovation Centre, Montreal, Quebec, Canada.
authors.forename: Ken
authors.initials: K
authors.lastname: Dewar
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de Médecine Vétérinaire, Université de Montréal, St-Hyacinthe, Quebec, Canada.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Gottschalk
authors.affiliation: Public Health Ontario, Toronto, Ontario, Canada; Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Nahuel
authors.initials: N
authors.lastname: Fittipaldi
mesh_terms: D000818:Animals; D002170:Canada; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D007564:Japan; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D011157:Population Dynamics; D013045:Species Specificity; D013290:Streptococcal Infections / Q000382:microbiology* / Q000662:veterinary; D017011:Streptococcus suis / Q000145:classification* / Q000302:isolation & purification / Q000472:pathogenicity*; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*; D014481:United States; D014774:Virulence
chemical_list: D004269:DNA, Bacterial