Food poisoning and Staphylococcus aureus enterotoxins

Abstract

Staphylococcus aureus produces a wide variety of toxins including staphylococcal enterotoxins (SEs; SEA to SEE, SEG to SEI, SER to SET) with demonstrated emetic activity, and staphylococcal-like (SEl) proteins, which are not emetic in a primate model (SElL and SElQ) or have yet to be tested (SElJ, SElK, SElM to SElP, SElU, SElU2 and SElV). SEs and SEls have been traditionally subdivided into classical (SEA to SEE) and new (SEG to SElU2) types. All possess superantigenic activity and are encoded by accessory genetic elements, including plasmids, prophages, pathogenicity islands, vSa genomic islands, or by genes located next to the staphylococcal cassette chromosome (SCC) implicated in methicillin resistance. SEs are a major cause of food poisoning, which typically occurs after ingestion of different foods, particularly processed meat and dairy products, contaminated with S. aureus by improper handling and subsequent storage at elevated temperatures. Symptoms are of rapid onset and include nausea and violent vomiting, with or without diarrhea. The illness is usually self-limiting and only occasionally it is severe enough to warrant hospitalization. SEA is the most common cause of staphylococcal food poisoning worldwide, but the involvement of other classical SEs has been also demonstrated. Of the new SE/SEls, only SEH have clearly been associated with food poisoning. However, genes encoding novel SEs as well as SEls with untested emetic activity are widely represented in S. aureus, and their role in pathogenesis may be underestimated.

Keywords: Staphylococcus aureus; emetic activity; food poisoning; gene location; staphylococcal enterotoxins; superantigens.

Figure 1

Enterotoxin and enterotoxin-like genes in plasmids pIB485 and pF5 based on sequencing data deposited under the accession numbers indicated to the right of the figure. Note thatpIB485 also contains blaZ and cad resistance genes [94] and probably ser [40,95].

Figure 2

Enterotoxin genes carried by prophages based on sequencing data deposited under the accession numbers indicated to the right of the figure.

Figure 3

Staphylococcus aureus pathogenicity islands (SaPIs) carrying enterotoxin or enterotoxin-like genes. Modified from Novick and Subedi [105] and based on the accession numbers indicated to the right of the figure.

Figure 4

Structure of two types of the vSaβ genomic island containing the enterotoxin gene cluster. Adapted from Baba et al. [108] and based on accession numbers indicated to the right of the figure.

Figure 5

Structure of egc clusters. Modified from Thomas et al [28] and Collery et al. [114], and based on the accession numbers indicated to the right of the figure.

Figure 6

Comparison of two allelic forms of SCC elements associated with seh. Modified from Noto and Archer [118] and based on the accession numbers indicated to the right of the figure.