Emetic Potentials of Newly Identified Staphylococcal Enterotoxin-Like Toxins

Abstract

g Staphylococcal enterotoxins (SEs) are a common causative agent of food poisoning. Recently, many new SE-like (SEl) toxins have been reported, although the role of SEls in food poisoning remains unclear. In this study, the emetic potentials of SElK, SElL, SElM, SElN, SElO, SElP, and SElQ were assessed using a monkey-feeding assay. All the SEls that were tested induced emetic reactions in monkeys at a dose of 100 g/kg, although the numbers of affected monkeys were significantly smaller than the numbers that were affected after consuming SEA or SEB. This result suggests that these new SEs may play some role in staphylococcal food poisoning. Staphylococcal enterotoxins (SEs) are exotoxins that cause staphylococcal food poisoning in humans worldwide (1-4). Several classical types (SEA, SEB, SEC, SED, and SEE) have been characterized (1, 2, 5). Recently, SEG, SEH, SEI, SER, SES, and SET were identified as potential agents of food poisoning (6-10). In addition, new proteins (SE-like toxin J [SElJ], SElK, SElL, SElM, SElN, SElO, SElP, SElQ, SElU, SElV, and SElX) with amino acid sequences that are similar to those of the above-mentioned SEs have been identified (11)(12)(13)(14)(15)(16)(17)(18)(19). SEs are also known to be members of the superantigen family (3,20). During the last few decades, numerous studies have been conducted on the nature of SEs and their superantigenic activities (3,20). However, the emetic activities of these toxins have not been studied. To better understand the etiologic nature of staphylococcal food poisoning, the emetic potentials of SEls should be evaluated in a primate model.We demonstrated the emetic activities of SElK, SElL, SElM, SElN, SElO, SElP, and SElQ using a primate model (cynomolgus monkeys); the number of vomiting events, the time until the first vomiting event (latency period), and behavioral changes were recorded for each animal. We compared the emetic activities of classical and new SEs as well as the activities of three large groups of SEs that were grouped according to the similarity of their amino acid sequences. MATERIALS AND METHODS Preparation of SEls.To construct the SElK, SElL, SElM, SElN, SElO, and SElQ expression plasmids, PCR primers were designed to amplify the gene fragment corresponding to the mature forms of these SEls (Table 1). The selk and selq genes were amplified from genomic DNA of the Staphylococcus aureus S6 strain, which harbors the sea, seb, selk, and selq genes (21). The sell gene was amplified from genomic DNA of the S. aureus bov1117 strain (harboring sea, sec, sell, sed, selj, selr, and tst-1), isolated from cow's milk, and the selm, seln, and selo genes were amplified from genomic DNA of the S. aureus Fukuoka 2 strain (21, 22). The PCR products were digested with BamHI and EcoRI or SalI and then subcloned into a pGEX6P-1 glutathione S-transferase (GST) fusion expression vector. These clones were designated pKKX (including the selk gene), pKLX (including the sell gene), pKMX (including the selm gene), pKNX (including the seln gene), pKOX (includin...

Staphylococcus aureus harbouring egc cluster coding for non-classical enterotoxins, involved in a food poisoning outbreak, Romania, 2012 / Staphylococcus aureus purtător de gene codante pentru enterotoxine non-clasice (cluster egc), implicat într-un focar de toxiinfecţie alimentară, România, 2012

“…In 2013, Omoe et al confirmed in a primate model the emetic potential of SElK, SElL, SElM, SElN, SElO, SElP, and SElQ (13).…”

“…A recent study confirmed the emetic potential of SElK, SElL, SElM, SElN, SElO, SElP, and SElQ in monkeys (cynomolgus monkeys) and proposed renaming them as SEK, SEL, SEM, SEN, SEO, SEP, and SEQ, respectively (13).…”

Production of staphylococcal enterotoxins in food

“…Uważa się, że najwyższą wrażliwością charakteryzuje się człowiek (6). Obecnie do badań wykorzystuje się małpy Macaca fascicularis oraz ryjówka domowego (Suncus murinus), ssaka należącego do rodziny ryjówkowatych (15,28). Wykorzystywanie małp wiąże się z wysokimi kosztami i pociąga za sobą wątpliwości natury etycznej.…”

“…W eksperymentach przeprowadzonych na małpach, przy doustnym lub dootrzewnowym podaniu enterotoksyn A, B, C 2 , D oraz E ustalono, że do wywołania efektu wymiotnego konieczne jest podanie zwierzęciu od 5 do 20 µg enterotoksyny (6). Badania przeprowadzone dotychczas wskazują, że aktywność wymiotna enterotoksyn klasycznych jest nawet 2-krotnie wyższa niż nowo opisanych czynników (28). Prace przeprowadzone przez Hu i wsp.…”

“…Stężenia SEA wytworzone przez szczepy S. aureus odpowiedzialne za zatrucia związane z tą toksyną wynosiły zaledwie 0,5-2 ng/ml (11,12). Są to dawki znacznie niższe niż te oszacowane w próbach biologicznych przeprowadzonych na zwierzętach (28).…”