Identification and Characterization of Staphylococcal Enterotoxin Types G and I from Staphylococcus aureus

Abstract

Staphylococcal enterotoxins are exotoxins produced byStaphylococcus 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 segand 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-γ), 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.

Prevalence and classification of toxigenic Staphylococcus aureus isolated from refrigerated ready-to-eat foods (sushi, kimbab and California rolls) in Korea

“…The involvement of the majority of the newly described SEs in food poisoning remains an open question (Lina et al 2004). The emetic toxicity of SEG and SEI, which were the most frequent genes detected in popular Korean RTE foods, was already confirmed, and the emetic doses were evaluated as 80 lg and 150 lg kg )1 of rhesus monkey weight, respectively (Munson et al 1998). These toxins also stimulate T-cell proliferation (superantigenic property).…”

“…Five classical SEs (SEA, SEB, SEC, SED and SEE) are the most common causes of staphylococcal food poisoning (Balaban and Rasooly 2000;Loir et al 2003). Furthermore, 16 new types of SEs or superantigens (SEG, SEH, SEI, SEJ, SEK, SEL, SEM, SEN, SEO, SEP, SEQ, SER, SES, SET, SEU and SEV) were recently described (Marry et al 1993;Ren et al 1994;Su and Wong 1995;Munson et al 1998;Zhang et al 1998;Fitzgerald et al 2001;Jarraud et al 2001;Kuroda et al 2001;Orwin et al 2001Orwin et al , 2002Orwin et al , 2003Yarwood et al 2002;Letertre et al 2003;Omoe et al 2003;Thomas et al 2006;Ono et al 2008).…”

Comprehensive analysis of classical and newly described staphylococcal superantigenic toxin genes inStaphylococcus aureusisolates

“…However, it is difficult to conclude that these newly identified SEs were responsible for these food poisoning outbreaks. The emetic activity of the newly described SEs has not been proved, except in the cases of SEG and SEI [5]. To confirm the relationship between these newly identified SEs and food poisoning, it is important to demonstrate the emetic activity of these newly described SEs using an experimental primate model.…”

“…SEs have been divided into five serological types (SEA though to SEE) based on their antigenicity [1]. In recent years, new types of SEs (SEG, SEH, SEI, SEJ, SEK, SEL, SEM, SEN, SEO, SEP, SEQ, SElR and SEU) have been reported [2,[5][6][7][8][9][10][11]. Several attempts to detect superantigenic toxin, SE and TSST-1 genes in S. aureus isolates have been made; these studies have shown that multiple superantigenic toxin genes are commonly found among S. aureus isolates [12][13][14][15][16][17].…”

Enterotoxin gene content inStaphylococcus aureusfrom the human intestinal tract

“…SEA to SEE, a number of new genes encoding enterotoxin homologues have been described recently (Thomas et al, 2007;Ono et al, 2008). Some of the new toxins, namely SEH, SEI, SEG, SER, SES, and SET, have been shown to have an emetic and enterotoxigenic effect (Su & Wong, 1995;Munson et al, 1998;Ono et al, 2008). The protein domain responsible for the induction of diarrhea has been located in the C-terminal 22-kDa fragment, obtained by trypsin digestion of SEC 1 .…”