Identification and Characterization of Two Novel Staphylococcal Enterotoxins, Types S and T

Abstract

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...

Superantigenic Toxin Genes Coexist with Specific Staphylococcal Cassette Chromosome mec Genes in Methicillin-Resistant Staphylococcus aureus

“…This leads to a massive release of proinflammatory cytokines and contributes to the severity of S. aureus sepsis (McCormick et al 2001;Holtfreter and Broker 2005). To date, 21 SEs have been identified based on sequence homologies (Becker et al 2003;Ono et al 2008). Although a few clinical studies have attempted to correlate toxic shock and outcome with the presence of certain SEs in patients with S. aureus infections (Kravitz et al 2005;Ferry et al 2008), the contribution of these toxins to outcome is still unclear.…”

High Incidence of Enterotoxin D ProducingStaphylococcusspp. in Brazilian Cow's Raw Milk and Its Relation with Coagulase and Thermonuclease Enzymes

“…The percentage of isolates producing enterotoxin type A was low. Currently, more than 20 types of staphylococcal enterotoxins are known (Balaban and Rasooly, 2000;Pereira et al, 1991;Munson et al, 1998;Orwin et al, 2001;Omoe et al, 2005;Thomas et al, 2006;Ono et al, 2008). However, enterotoxin A is the most commonly staphylococcal enterotoxin associated with foodborne outbreaks, followed by enterotoxin D (Balaban and Rasooly, 2000).…”

Staphylococcal Enterotoxins, Stayphylococcal Enterotoxin B and Bioterrorism

“…In 2001, a cluster of genes with homologies to SE genes was identified and named the enterotoxin gene cluster (egc). Since many of the genes produced SE-like proteins, Jarraud et al (2001) suggested that the gene cluster formed an enterotoxin nursery where genomic rearrangements would lead to new SEs, a fact that has now been confirmed with the development of the new exotoxin SEG (Lindsay, 2011;Thomas et al, 2006 (Uchiyama et al, 2003;Ono et al, 2008) b Gene location of the toxin c enterotoxin gene cluster d Staphylococcus aureus phatogeniciti islands Table 1. Staphylococcal enterotoxin/superantigens…”

“…Using the Clustal W program, the amino acid sequences of the SEs were aligned and evolutionary distances determined. A dendrogram constructed by the near neighbor-joining method divides the toxins into three major and two minor monophyletic groups (Ono et al, 2008;Uchiyama et al, 2003). The first two groups contain the classical toxins SEA, SED, SEE (Group 1) and SEB, SEC (Group 2) in addition to newly identified SEs; Group 3 contains only newly identified toxins.…”