title: Streptococcus suis serotype 2 mutants deficient in capsular expression.
abstract: Streptococcus suis serotype 2 is responsible for a wide variety of porcine infections. In addition, it is considered a zoonotic agent. Knowledge about the virulence factors for this bacterium is limited but its polysaccharide capsule is thought to be one of the most important. Transposon mutagenesis with the self-conjugative transposon Tn916 was used to obtain acapsular mutants from the virulent S. suis type 2 reference strain S735. Clones were screened by colony-dot ELISA with a monoclonal antibody specific for a type 2 capsular epitope and clones that failed to react with the antibody were characterized. Two mutants, 2A and 79, having one and two Tn916 insertions respectively, were chosen for further characterization. Absence of capsule was confirmed by coagglutination, capillary precipitation and capsular reaction tests and by transmission electron microscopy. Absence of capsular polysaccharides correlated with increased hydrophobicity and phagocytosis by both murine macrophages and porcine monocytes compared to the wild-type strain. Furthermore, both mutants were shown to be avirulent in murine and pig models of infection. Finally, mutant 2A was readily eliminated from circulation in mice compared to the wild-type strain, which persisted more than 48 h in blood. Thus, isogenic mutants defective in capsule production demonstrate the importance of capsular polysaccharides as a virulence factor for S. suis type 2.
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de médecine vétérinaire, Université de Montréal, CP 5000, St-Hyacinthe, Québec, Canada J2S 7C6.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Charland
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de médecine vétérinaire, Université de Montréal, CP 5000, St-Hyacinthe, Québec, Canada J2S 7C6.
authors.forename: Josée
authors.initials: J
authors.lastname: Harel
authors.affiliation: Centre National d'Études Vétérinaires et alimentaires, Unité Mycoplasmologie Bactériologie, BP 53, Zoopôle, 22440 Ploufragan, France.
authors.forename: Marylène
authors.initials: M
authors.lastname: Kobisch
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de médecine vétérinaire, Université de Montréal, CP 5000, St-Hyacinthe, Québec, Canada J2S 7C6.
authors.forename: Serge
authors.initials: S
authors.lastname: Lacasse
authors.affiliation: Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de médecine vétérinaire, Université de Montréal, CP 5000, St-Hyacinthe, Québec, Canada J2S 7C6.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Gottschalk
mesh_terms: D000372:Agglutination Tests; D000818:Animals; D000911:Antibodies, Monoclonal; D016667:Bacterial Capsules / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D001681:Biological Assay; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D015870:Gene Expression; D005798:Genes, Bacterial; D006460:Hemolysin Proteins / Q000378:metabolism; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008854:Microscopy, Electron; D009000:Monocytes / Q000382:microbiology; D016254:Mutagenesis, Insertional; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D010587:Phagocytosis / Q000235:genetics; D013290:Streptococcal Infections / Q000235:genetics* / Q000276:immunology; D017011:Streptococcus suis / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D014774:Virulence / Q000235:genetics
chemical_list: D000911:Antibodies, Monoclonal; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D006460:Hemolysin Proteins; D019158:N-Acetylneuraminic Acid