To investigate the distribution of staphylococcal enterotoxin (SE) A to I (SEA to SEI) genes (sea to sei) in Staphylococcus aureus, 146 isolates obtained in Japan from humans involved in and samples from food poisoning outbreaks, healthy humans, cows with mastitis, and bovine raw milk were analyzed by multiplex PCR. One hundred thirteen (77.4%) S. aureus isolates were found to be positive for one or more se genes. The se genotype was classified into 14 genotypes. seg and sei coexisted in the same S. aureus strain. The newly developed sandwich enzyme-linked immunosorbent assay showed that most seh-harboring S. aureus isolates were able to produce a significant amount of SEH. However, most of the S. aureus isolates harboring seg and about 60% of the isolates harboring sei did not produce a detectable level of SEG or SEI, while reverse transcription-PCR analysis proved that the mRNAs of SEG and SEI were transcribed in S. aureus strains harboring seg and sei genes. These results suggest the importance of quantitative assessment of SEG and SEI production in foods in order to clarify the relationship between these new SEs and food poisoning

We describe a comprehensive detection system for 18 kinds of classical and newly described staphylococcal superantigenic toxin genes using four sets of multiplex PCR. Superantigenic toxin genotyping of Staphylococcus aureus for 69 food poisoning isolates and 97 healthy human nasal swab isolates revealed 32 superantigenic toxin genotypes and showed that many S. aureus isolates harbored multiple toxin genes. Analysis of the relationship between toxin genotypes and toxin genes encoding profiles of mobile genetic elements suggests its possible role in determining superantigenic toxin genotypes in S. aureus as combinations of toxin gene-encoding mobile genetic elements.

In addition to two known staphylococcal enterotoxin-like genes (selj and selr), two novel genes coding for two superantigens, staphylococcal enterotoxins S and T (SES and SET), were identified in plasmid pF5, which is harbored by food poisoning-related Staphylococcus aureus strain Fukuoka 5. This strain was implicated in a food poisoning incident in Fukuoka City, Japan, in 1997. Recombinant SES (rSES) specifically stimulated human T cells in a T-cell receptor V␤9-and V␤16-specific manner in the presence of major histocompatibility complex (MHC) class II ؉ antigen-presenting cells (APC). rSET also stimulated T cells in the presence of MHC class II ؉ APC, although its V␤ skewing was not found in reactive T cells. Subsequently, we examined the emetic activity of SES and SET. We also studied SElR to determine emetic activity in primates. This toxin was identified in previous studies but was not examined in terms of possession of emetic activity for primates. rSES induced emetic reactions in two of four monkeys at a dose of 100 g/kg within 5 h of intragastric administration. In one monkey, rSET induced a delayed reaction (24 h postadministration) at a dose of 100 g/kg, and in the other one, the reaction occurred 5 days postadministration. rSElR induced a reaction in two of six animals within 5 h at 100 g/kg. On this basis, we speculate that the causative toxins of vomiting in the Fukuoka case are SES and SER. Additionally, SES, SER, and SET also induced emesis in house musk shrews as in the monkeys.Staphylococcus aureus produces a variety of superantigenic toxins (SAGTs), which selectively activate a vast number of T cells, depending on V␤ elements in the ␤ chain of a T-cell receptor (TCR), in direct association with major histocompatibility complex (MHC) class II molecules on antigen-presenting cells (APC) (14, 31). Staphylococcal SAGTs can be divided into three large groups and one minor group on the basis of similarity of amino acid sequences (31). Most toxins of the three groups, including staphylococcal enterotoxins A and B (SEA and SEB), exhibit strong emetic activity in primates (4, 16, 25); toxic shock syndrome toxin-1, grouped as the minor group, does not possess emetic activity in primates (14, 31). It is noteworthy that toxins designated SE-like toxins, such as SElP and SElR, which either have not been examined for emetic activity or have been reported not to have emetic activity, have been discovered in S. aureus strains (12,13,20,27). S. aureus strain Fukuoka 5 was isolated from food as the causative microbe in a food poisoning outbreak in Fukuoka City, Japan, in 1997, although this strain did not carry any well-recognized SAGT genes with emetic activity (19). Subsequently, Omoe et al. (19) discovered, using a plaque hybridization with a seg probe, that 2.8 kbp of the EcoRI fragment of plasmid pF5, carried by Fukuoka 5, carries two genes, a novel SAGT gene designated selr and a previously reported gene, selj (33).We undertook research to explore, using a PCR walking technique, whether there were addition...

We identified and characterized a novel staphylococcal enterotoxin-like putative toxin, which is named SER. Nucleotide sequencing analysis of the ser gene revealed that ser was most closely related to the seg gene. The ser gene product, SER, was successfully expressed as a recombinant protein in an Escherichia coli expression system, and recombinant SER (rSER) showed significant T-cell stimulation activity. The SER production in ser-harboring Staphylococcus aureus strains was confirmed by Western blot analysis using anti-rSER antibody. Moreover, ser was seen to be encoded by at least two types of plasmids. In particular, one kind of plasmid encoding the ser gene has been known as a sed-and sej-carrying pIB485-related plasmid.

To investigate whether vaccination with nontoxic mutant toxic shock syndrome toxin 1 (mTSST-1) can protect against Staphylococcus aureus infection, mice were vaccinated with mTSST-1 and challenged with viable S. aureus. Survival in the mTSST-1-vaccinated group was higher, and bacterial counts in organs were significantly lower than those of control mice. Passive transfer of mTSST-1-specific antibodies also provided protection against S. aureus-induced septic death. Interferon (IFN)-gamma production in the serum samples and spleens from vaccinated mice was significantly decreased compared with that in controls, whereas interleukin-10 titers were significantly higher in vaccinated mice. IFN-gamma and tumor necrosis factor-alpha production in vitro were significantly inhibited by serum samples from mTSST-1-immunized mice but not from control mice. These results suggest that vaccination with mTSST-1 devoid of superantigenic properties provides protection against S. aureus infection and that the protection might be mediated by TSST-1-neutralizing antibodies as well as by the down-regulation of IFN-gamma production.