Infect Immun, July 1998, p. 3337-3348, Vol. 66, No. 7
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

and
Department of
Bacteriology1 and
Department of Medical
Microbiology and Immunology,2 University of
Wisconsin
Madison, Madison, Wisconsin 53706
Received 29 December 1997/Returned for modification 11 February 1998/Accepted 21 April 1998
Staphylococcal enterotoxins are exotoxins produced by
Staphylococcus aureus that possess emetic and
superantigenic properties. Prior to this research there were six
characterized enterotoxins, staphylococcal enterotoxin types A to E and
H (referred to as SEA to SEE and SEH). Two new staphylococcal
enterotoxin genes have been identified and designated seg
and sei (staphylococcal enterotoxin types G and I,
respectively). seg and sei consist of 777 and
729 nucleotides, respectively, encoding precursor proteins of 258 (SEG)
and 242 (SEI) deduced amino acids. SEG and SEI have typical bacterial
signal sequences that are cleaved to form toxins with 233 (SEG) and 218 (SEI, predicted) amino acids, corresponding to mature proteins of
27,043 Da (SEG) and 24,928 Da (SEI). Biological activities for SEG and
SEI were determined with recombinant S. aureus strains. SEG
and SEI elicited emetic responses in rhesus monkeys upon nasogastric
administration and stimulated murine T-cell proliferation with the
concomitant production of interleukin 2 (IL-2) and gamma interferon
(IFN-
), as measured by cytokine enzyme-linked immunoassays. SEG and
SEI are related to other enterotoxins of S. aureus and to
streptococcal pyrogenic exotoxin A (SpeA) and streptococcal
superantigen (SSA) of Streptococcus pyogenes. Phylogenetic
analysis and comparisons of amino acid and nucleotide sequence
identities were performed on related staphylococcal and streptococcal
protein toxins to group SEG and SEI among the characterized toxins. SEG
is most similar to SpeA, SEB, SEC, and SSA (38 to 42% amino acid
identity), while SEI is most similar to SEA, SEE, and SED (26 to 28%
amino acid identity). Polyclonal antiserum was generated against
purified histidine-tagged SEG and SEI (HisSEG and HisSEI). Immunoblot
analysis of the enterotoxins, toxic-shock syndrome toxin 1, and SpeA
with antiserum prepared against HisSEG and HisSEI revealed that SEG
shares some epitopes with SEC1 while SEI does not.
Present address: Monsanto, Agracetus Campus, Middleton, WI, 53562.
Deceased.
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