title: Identification of a streptolysin S-associated gene cluster and its role in the pathogenesis of Streptococcus iniae disease.
abstract: Streptococcus iniae causes meningoencephalitis and death in cultured fish species and soft-tissue infection in humans. We recently reported that S. iniae is responsible for local tissue necrosis and bacteremia in a murine subcutaneous infection model. The ability to cause bacteremia in this model is associated with a genetic profile unique to strains responsible for disease in fish and humans (J. D. Fuller, D. J. Bast, V. Nizet, D. E. Low, and J. C. S. de Azavedo, Infect. Immun. 69:1994-2000, 2001). S. iniae produces a cytolysin that confers a hemolytic phenotype on blood agar media. In this study, we characterized the genomic region responsible for S. iniae cytolysin production and assessed its contribution to virulence. Transposon (Tn917) mutant libraries of commensal and disease-associated S. iniae strains were generated and screened for loss of hemolytic activity. Analysis of two nonhemolytic mutants identified a chromosomal locus comprising 9 genes with 73% homology to the group A streptococcus (GAS) sag operon for streptolysin S (SLS) biosynthesis. Confirmation that the S. iniae cytolysin is a functional homologue of SLS was achieved by PCR ligation mutagenesis, complementation of an SLS-negative GAS mutant, and use of the SLS inhibitor trypan blue. SLS-negative sagB mutants were compared to their wild-type S. iniae parent strains in the murine model and in human whole-blood killing assays. These studies demonstrated that S. iniae SLS expression is required for local tissue necrosis but does not contribute to the establishment of bacteremia or to resistance to phagocytic clearance.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Fuller
authors.forename: Alvin C
authors.initials: AC
authors.lastname: Camus
authors.forename: Carla L
authors.initials: CL
authors.lastname: Duncan
authors.forename: Victor
authors.initials: V
authors.lastname: Nizet
authors.forename: Darrin J
authors.initials: DJ
authors.lastname: Bast
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Thune
authors.forename: Donald E
authors.initials: DE
authors.lastname: Low
authors.forename: Joyce C S
authors.initials: JC
authors.lastname: De Azavedo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins; D001483:Base Sequence; D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000235:genetics; D004195:Disease Models, Animal; D005260:Female; D005399:Fishes; D015870:Gene Expression; D005798:Genes, Bacterial; D006461:Hemolysis / Q000235:genetics; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D010587:Phagocytosis; D017386:Sequence Homology, Amino Acid; D013290:Streptococcal Infections / Q000209:etiology*; D013291:Streptococcus / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity*; D013301:Streptolysins / Q000235:genetics*; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D013301:Streptolysins; C026050:streptolysin S