**2.9 Endotoxin of** *Salmonella* **Typhi**

Endotoxin is a big part of Gram-negative bacteria's outer membrane (OM). Endotoxins have been found to play an important function in the pathogenicity of Gram-negative bacterial infections. It is a powerful mediator of a wide range of pathophysiological effects in humans, mainly in the gasterointestinal tracts. Therefore, these are also known as enterotoxins. These toxic behaviors, as well as many beneficial ones linked to immunostimulation, include lethal toxicity, pyrogenicity and tissue necrotizing activity [42]. Endotoxins are high-molecular weight complexes, of lipopolysaccharides (LPS) which is the major component of bacterial cell wall [42]. It's a heat stable toxic substance released by gram negative bacteria's after disruption of cell envelopes [43, 44]. The role of endotoxins in bacterial pathogenesis and their chemical characterization as lipopolysaccharide (LPS) have been studied earlier [45, 46]. Chemically, LPS consist of a hydrophilic polysaccharide covalently linked to a hydrophobic lipid portion which is termed as lipid A, which anchors the molecules in the outer membrane (OM) [47]. Endotoxins play a major role in human disease states that created interest to investigate the pathogenicity of the producing bacteria [42]. Lipopolysaccharide found to be an important activator for the activation of immune system that leads to non- specific inflammatory immune response [48].
