title: Se18.9, an anti-phagocytic factor H binding protein of Streptococcus equi.
abstract: Evasion of phagocytosis is an important virulence determinant of Streptococcus equi (S. equi subsp. equi), the cause of equine strangles and distinguishes it from the closely related but much less virulent S. zooepidemicus (S. equi subsp. zooepidemicus). We describe Se18.9, a novel H factor binding protein secreted by S. equi but not by S. zooepidemicus that reduces deposition of C3 on the bacterial surface and significantly reduces the bactericidal activity of equine neutrophils suspended in normal serum for both S. equi and S. zooepidemicus. Se18.9 is secreted abundantly by actively dividing cells and is also bound to the bacterial surface. Strong serum and mucosal antibody responses are elicited in S. equi infected horses. Although a gene identical to se18.9 was not detected in S. zooepidemicus, sequences encoding proteins of similar size with similar signal peptide sequences were found in 3 of 12 randomly selected strains. Since Se18.9 is unique to S. equi, and immunoreactive with convalescent sera and mucosal IgA, it has potential for immunodiagnosis and for study of mucosal antibody response to S. equi.
authors.affiliation: 325 M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA.
authors.forename: Raksha
authors.initials: R
authors.lastname: Tiwari
authors.forename: Aiping
authors.initials: A
authors.lastname: Qin
authors.forename: Sergey
authors.initials: S
authors.lastname: Artiushin
authors.forename: John F
authors.initials: JF
authors.lastname: Timoney
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D001483:Base Sequence; D003001:Cloning, Molecular; D017242:Complement Factor H / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses; D015151:Immunoblotting / Q000662:veterinary; D008199:Lymphadenitis / Q000382:microbiology / Q000662:veterinary*; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000276:immunology; D010587:Phagocytosis / Q000276:immunology; D016133:Polymerase Chain Reaction / Q000662:veterinary; D013290:Streptococcal Infections / Q000382:microbiology / Q000662:veterinary*; D018502:Streptococcus equi / Q000276:immunology / Q000378:metabolism / Q000472:pathogenicity / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D017242:Complement Factor H