Staphylococcal Enterotoxins (SEs): Types, Mechanisms, and Detection Methods

Classical Staphylococcal Enterotoxins (SEs)

The initial group of SEs was identified as classical enterotoxins. The major serotypes within this group consist of SEA, SEB, SEC, SED and SEE. The food poisoning outbreaks are primarily caused by SEA which stands as one of the most prevalent and dangerous serotypes. The classical toxins have received extensive research which proves their role in foodborne illnesses. The primary cause of staphylococcal food poisoning stems from Staphylococcus aureus proteins known as Staphylococcal Enterotoxins (SEs) which function as superantigens to induce emesis. All enterotoxins belong to the same category yet they exhibit different structural characteristics and varying levels of potency and disease associations.
Table 1. Unique features of some common SEs.

Novel Staphylococcal Enterotoxins (SEs)

Molecular biology techniques have enabled scientists to identify various new enterotoxins which have expanded the enterotoxin family. The new enterotoxins discovered include SEG, SEH, SEI, SEJ, SEK, SEL, SEM, SEN, SEO, SEP, SEQ, SER, SES, SET, SEU, SEV, and SEIX. Some of these novel enterotoxins, such as SE1K through SE1Q, have been shown to exhibit emetic activity in animal studies. However, compared to traditional enterotoxins, direct studies linking many novel enterotoxins to human food poisoning are still understudied. The total number of reported enterotoxins has reached 23 to 24.

Classification of SEs

The International Nomenclature Committee for Staphylococcal Superantigens (INCSS) proposed that only toxins demonstrating emetic effects after oral administration in a primate model should be specifically classified as SEs. Conversely, other toxins associated with Staphylococcal food poisoning, which either do not exhibit emetic properties in this model or have not undergone testing, should be labelled as "staphylococcal enterotoxin-like" (SEl) superantigens.

Figure 1. The structure diagram of SEs and SEls in each Group. (Shen, 2025)

The amino acid sequences and structural features of SEs and SEls enable their classification into four phylogenetic groups which include TSST-1, SElX, SElY in Group I and SEB, SEC, SEG, SEU, SElU2, SEl27, SE02 in Group II and SEA, SED, SEE, SEH, SEJ, SEN, SEO, SEP, SE01 in Group III and SEI, SEK, SEL, SEM, SEQ, SER, SES, SET, SElV, SEl26 in Group V (NB: Group IV contains superantigens from streptococcal bacteria). Staphylococcal Enterotoxins (SEs) Mechanisms of Action

Assays for Enterotoxins

The detection methods for staphylococcal enterotoxins differ in their sensitivity levels and practicality and application scope. Traditional animal bioassays for toxin detection remain expensive and raise ethical concerns while providing insufficient sensitivity for regular use but molecular techniques including PCR, qPCR and WGS enable reliable enterotoxin gene identification without direct toxin measurement and require pathogen isolation. The practical application of polymer-based biosensors and aptamers remains restricted because these detection methods are still experimental and experience interference from matrix components. The detection sensitivity of earlier immunological methods (OSP, RIA, latex agglutination) was insufficient but ELISA became the gold standard because it offers accuracy and simplicity and works with various samples and detects both traditional and non-traditional enterotoxins through sandwich formats with polyclonal and monoclonal antibodies. The commercial application of hydrogel-based immunobiochips for multiplex toxin detection remains restricted despite their demonstrated potential for this purpose.