Biological characteristics of staphylococcal enterotoxin Q and its potential risk for food poisoning.

AIMS: To elucidate the biological characteristics and stability of a newly identified staphylococcal enterotoxin Q (SEQ) against heating and digestive enzymes and to evaluate the risk of seq-harbouring Staphylococcus aureus in food poisoning. METHODS AND RESULTS: Purified SEQ was treated with heating, pepsin and trypsin which are related to food cooking, stomach and intestine conditions, respectively. Superantigenic activity of SEQ was assessed by determining the ability of IL-2 induction in mouse spleen cells. The emetic activity of SEQ was assessed using house musk shrew, a small emetic animal model. The results revealed that SEQ exhibits a remarkable resistance to heat treatment and pepsin digestion and has significant superantigenic and emetic activities. Furthermore, a sandwich ELISA for detection of SEQ production was developed, and the results showed that seq-harboring S. aureus isolates produce a large amount of SEQ. CONCLUSIONS: The newly identified SEQ had remarkable stability to heat treatment and digestive enzyme degradation and exhibited significant superantigenic and emetic activities. In addition, seq-harbouring S. aureus isolated from food poisoning outbreaks produced a large amount of SEQ, suggesting that seq-harbouring S. aureus could potentially be a hazard for food safety. SIGNIFICANCE AND IMPACT OF THE STUDY: This study found, for the first time, that SEQ, a nonclassical SE, had remarkable stability to heat treatment and enzyme degradation and exhibited significant emetic activity, indicating that SEQ is a high-risk toxin in food poisoning.

Goblet cells are involved in translocation of staphylococcal enterotoxin A in the intestinal tissue of house musk shrew (Suncus murinus).

AIMS: To elucidate an entry site of staphylococcal enterotoxin A (SEA), which is a major toxin for staphylococcal foodborne poisoning, into gastrointestinal tissue using a house musk shrew model. METHODS AND RESULTS: House musk shrews were per orally administered with recombinant SEA and localization of SEA in gastrointestinal tissues was investigated by immunohistochemistry and immunoelectron microscopy 30 min after administration. SEA was detected in a subset of intestinal epithelial cells and lamina propria in the villi of jejunum and ileum. This observation was also found in gastrointestinal loops. Morphological characteristics of the SEA-immunopositive cells indicated that goblet cells are an entry site of SEA.SEA entered mucus-expelling goblet cells and the induction of mucus secretion by alyll isothiocyanate resulted in an intensive SEA signal. These results suggest that mucus secretion by goblet cells is important for the translocation of SEA. CONCLUSIONS: SEA can translocate across intestinal epithelia via mucus-expelling goblet cells. SIGNIFICANCE AND IMPACTS OF THE STUDY: An entry site of SEA during translocation across the gastrointestinal mucosal barrier was investigated. This study was the first to demonstrate the significance of goblet cells as an entry site of this bacterial toxin.

Identification and characterization of novel Staphylococcus aureus pathogenicity islands encoding staphylococcal enterotoxins originating from staphylococcal food poisoning isolates.

AIMS: Horizontal transfer of Staphylococcus aureus pathogenicity islands (SaPIs) plays an important role in acquiring pathogenicity. This study aimed to identify novel SaPIs encoding staphylococcal enterotoxins (SEs) and to characterize their SE productivity and replication process. METHODS AND RESULTS: Four novel SaPIs (SaPITokyo12413, SaPITokyo11212, SaPITokyo12571 and SaPITokyo12381) were determined using the SaPI scanning method. These SaPIs were composed of mosaic structures containing reported sequences. Four strains harbouring novel SaPIs produced significant amounts of SEs to cause staphylococcal food poisoning (SFP). With focus on the interaction between the replication initiator protein (Rep) and the replication origin (ori sites) that are proposed to be important for the replication of SaPIs, each Rep was prepared and their two functions were confirmed: binding activity to ori sites and helicase activity. These activities were present in the Reps of SaPITokyo11212, SaPITokyo12571 and SaPITokyo12381, but were both absent in the Rep of SaPITokyo12413. CONCLUSIONS: All four novel SaPIs could give sufficient toxicity to Staph. aureus to cause SFP. However, SaPITokyo12413 may be restricted in its replication capacity, suggesting that it lacks transfer ability unlike the other SaPIs. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report to identify four novel SE-encoding SaPIs and to examine their toxicity and replication capacity. Because SaPIs deeply participate in SE acquisition, it is important to elucidate their characteristics for understanding Staph. aureus virulence and speculating regarding its evolution as a pathogen.