**2. Endotoxin**

The endotoxin is integral part of outer membrane in gram negative cell wall. The gram negative bacteria consists of the inner membrane, outer membrane and peptidoglycan layer. The inner membrane is permeable layer while outer membrane consists of lipopolysaccride layer and generally protects the cell from outer stress. So endotoxins are associated with the lipopolysaccharide (LPS). Generally endotoxin structure consist of three parts i.e., lipid A component made up of "disaccharide phosphates and fatty acids," an O-specific polysaccharide side chain (O-antigen), and a core polysaccharide chain" weighing approximately 10 kDa (**Figure 1**). The core polysaccharide added to lipid A sequentially during the formation of the lipid polysaccharide chain. The O-antigen's subunits are attached at the end of polysaccharide chain. But the most harmful' harmful part is lipid A [4]. Various gram negative bacterial species having different endotoxin structure. The different in structure is due to composition of the O-antigen or Lipid A component, bacterial strains as well as environmental conditions. The O-antigen involved in the antigensity and Lipid A determines the toxicity and inflammation by detecting the myeloid differentiation factor II and toll IV receptors (MD2/TLR4) [5]. Endotoxins are heat stable, negatively charged and hydrophobic in nature. They also form aggregate in the form of vesicles or micelles with size ranges about 10–20 kDa in monomer) and more than 1000 kDa in vesicles [6].
