Identification of three novel superantigen-encoding genes in Streptococcus equi subsp. zooepidemicus, szeF, szeN, and szeP.
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-α) and gamma interferon (IFN-γ) 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.
Paillot
Romain
R
Centre for Preventive Medicine, Animal Health Trust, Kentford, Newmarket, Suffolk, United Kingdom.
Darby
Alistair C
AC
Robinson
Carl
C
Wright
Nicola L
NL
Steward
Karen F
KF
Anderson
Emma
E
Webb
Katy
K
Holden
Matthew T G
MT
Efstratiou
Androulla
A
Broughton
Karen
K
Jolley
Keith A
KA
Priestnall
Simon L
SL
Marotti Campi
Maria C
MC
Hughes
Margaret A
MA
Radford
Alan
A
Erles
Kerstin
K
Waller
Andrew S
AS
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D004283:Dog Diseases / Q000382:microbiology; D004285:Dogs; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D006734:Horse Diseases / Q000276:immunology / Q000382:microbiology; D006736:Horses; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000276:immunology / Q000382:microbiology* / Q000662:veterinary; D018502:Streptococcus equi / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification / Q000472:pathogenicity; D018089:Superantigens / Q000235:genetics* / Q000276:immunology
D004269:DNA, Bacterial; D018089:Superantigens