Molecular characterization and phylogenetic distribution of the streptococcal superantigen gene (ssa) from Streptococcus pyogenes

K. B. Reda, V. Kapur, J. A. Mollick, J. G. Lamphear, J. M. Musser, R. R. Rich

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Abstract

A striking increase in the frequency and severity of invasive infections caused by Streptococcus pyogenes has occurred in recent years. Among these diseases is streptococcal toxic-shock-like syndrome (TSLS), a condition characterized by fulminant soft-tissue destruction and multiorgan failure. Streptococcal superantigen (SSA), a superantigen isolated from a TSLS- inducing, serotype M3 S. pyogenes strain, has recently been identified. We here describe the cloning, sequencing, and phylogenetic distribution of the SSA structural gene. The 783-bp open reading frame encodes a predicted 260- amino-acid protein that is similar in size to several other bacterial superantigens. The deduced sequence of the mature protein is 60.2% identical to that of staphylococcal enterotoxin B but only 49% identical to that of streptococcal pyrogenic exotoxin A. Southern blot and PCR analysis of 138 group A streptococcal strains representing 65 M protein serotypes and 15 nontypeable isolates, identified ssa in 68 strains from 10 distinct clonal lineages. All ssa-positive clones expressed SSA. Of the two clones associated with TSLS, the ET 2-M3 lineage, but not the ET 1-M1 lineage, carried the SSA gene. Further analysis of the ET 2-M3 lineage found evidence for temporal variation in ssa association. Contemporary ET 2-M3 disease isolates had ssa, but two older isolates of this clone recovered in 1910 and 1920 lacked the gene. The clonal and temporal distribution patterns of ssa suggest a relatively recent acquisition of this superantigen-encoding gene by the ET 2- M3 lineage, perhaps by horizontal transfer and recombination.

Original languageEnglish (US)
Pages (from-to)1867-1874
Number of pages8
JournalInfection and Immunity
Volume62
Issue number5
StatePublished - Jan 1 1994

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All Science Journal Classification (ASJC) codes

  • Parasitology
  • Microbiology
  • Immunology
  • Infectious Diseases

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