*3.4.2 Staphylococcal enterotoxins (SEs)*

These toxins are released by pathogenic bacterial strain that are responsible for food spoilage or poisoning. These are classified as staphylococcal enterotoxins and cholera toxins (AB5 group enterotoxins) Shiga toxins and heat-labile toxins (Escherichia coli) [57]. But the most significant among all enterotoxin is *Staphylococcus aureus* enterotoxins (SEs). SEs are known as super antigen, capable to activate T lymphocytes (~20–30%), as a result overproduction of cytokines is occurred, which are responsible for inflammation [58]. *Staphylococcus aureus,* is widely spread and rapidly growing toxin producing bacterium. In humans this bacterium is colonizes in the throat, nasal cavity, and crotch/anus of human body and usually resistant to antibiotics. It is also present in meat and dairy products [59, 60].

SEs having mass of 26–35 kDa proteins, containing a single polypeptide chains. Two unequal size domains are mainly composed of alpha (α) helices and beta |(β) strand separated by a deep shallow groove and having complex tertiary structure. These SEs proteins are highly solubilized in both salt and water. It is also resistant to proteolytic enzymes including papain pepsin, rennin and trypsin, thus remain unchanged in the gastrointestinal tract. These toxins are also resistant to dehydration, gamma radiation, and a wide pH range (2 < pH < 12) [30, 61, 62]. SEs gene

coding region is present on plasmids, prophages, *S. aureus* pathogenicity islands and genomic island vSa, (SaPIs) [62]. These Super antigens are categorized in class II Major Histocompatibility Complex (MHC) molecules but the binding groove of MHC peptide-antigen is not involved. The SEs has four types A,B,C and D. A and D usually involved in natural food poisoning rarely by the B and C types [63, 64]. The most potent and lethal SEs enterotoxin is type B (SEB) and used in bioterrorism so termed as biological weapon. It is highly thermo stable heat resistant toxins and is detected even in sterilized food. In human it also cause toxic shock syndrome and severe food poisoning that leads to dehydration and ultimately death occur. If this toxin id enter into the body other via food or through inhalation, induces a septic response throughout the living organism. The toxicity levels for this type of poisoning are LD50 20 μg/ kg and ED50 400 ng/kg [61, 65, 66].
