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Lipopolysaccharide (LPS) is a conjugated biomolecule that consists of polysaccharides covalently bound to lipid. It is also known as lipoglycan and is prominently located in the outer membrane of Gram-negative bacteria. Liposaccharides are more notorious due to their pathogenic nature. The toxicity of LPS was first time reported by Richard Friedrich Johannes Pfeiffer who coined the name of bacterial endotoxin. The endotoxin is secreted by live bacterial cells and as well as after their cell degradation. Endotoxin acts as strong antigen and can elicit body immune response. Despite the pathogenic nature of LPS, it helps the bacteria in adhesion and bacteriophage sensitivity, etc. [57, 58].

The LPS have three further components such as: O-antigen, Core polysaccharides and lipid-A. The O-antigen is composed of the long chain of the repetitive glycans subunits and is also known as O-polysaccharides. O-antigen has been attached to the very end of the LPS molecules and it may vary from one bacterial strain to another. The core polysaccharides itself is composed of oligosaccharide sugars such as heptose and 3-deoxy-damnnnoocutlsonics acid and being attached to lipid-A. The third part of the LPS is lipid-A, which has been considered the most conserved region of the LPS and consist of disaccharides like, phosphorylated glucosamine being attached to many fatty acids. Being the hydrophobic nature of the fatty acids lead the anchoring of the lipid-A into bacterial membrane. Lipid-A is highly antigenic in nature and responsible for the pathogenicity of Gram-negative bacteria. When the cell lysed then the lipid-A set out into blood and induce septic shock, fever and diarrhea [59–61].