Identification of Three Novel Superantigen-Encoding Genes in Streptococcus equi subsp zooepidemicus, szeF, szeN, and szeP

Romain Paillot, Alistair C. Darby, Carl Robinson, Nicola L. Wright, Karen F. Steward, Emma Anderson, Katy Webb, Matthew T. G. Holden, Androulla Efstratiou, Karen Broughton, Keith A. Jolley, Simon L. Priestnall, Maria C. Marotti Campi, Margaret A. Hughes, Alan Radford, Kerstin Erles, Andrew S. Waller*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

57 Citations (Scopus)


The acquisition of superantigen-encoding genes by Streptococcus pyogenes has been associated with increased morbidity and mortality in humans, and the gain of four superantigens by Streptococcus equi is linked to the evolution of this host-restricted pathogen from an ancestral strain of the opportunistic pathogen Streptococcus equi subsp. zooepidemicus. A recent study determined that the culture supernatants of several S. equi subsp. zooepidemicus strains possessed mitogenic activity but lacked known superantigen-encoding genes. Here, we report the identification and activities of three novel superantigen-encoding genes. The products of szeF, szeN, and szeP share 59%, 49%, and 34% amino acid sequence identity with SPEH, SPEM, and SPEL, respectively. Recombinant SzeF, SzeN, and SzeP stimulated the proliferation of equine peripheral blood mononuclear cells, and tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) production, in vitro. Although none of these superantigen genes were encoded within functional prophage elements, szeN and szeP were located next to a prophage remnant, suggesting that they were acquired by horizontal transfer. Eighty-one of 165 diverse S. equi subsp. zooepidemicus strains screened, including 7 out of 15 isolates from cases of disease in humans, contained at least one of these new superantigen-encoding genes. The presence of szeN or szeP, but not szeF, was significantly associated with mitogenic activity in the S. equi subsp. zooepidemicus population (P <0.000001, P <0.000001, and P = 0.104, respectively). We conclude that horizontal transfer of these novel superantigens from and within the diverse S. equi subsp. zooepidemicus population is likely to have implications for veterinary and human disease.

Original languageEnglish
Pages (from-to)4817-4827
Number of pages11
JournalInfection and Immunity
Issue number11
Publication statusPublished - Nov 2010




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