![]() ![]() He distinguished between exotoxins, toxins that are released by bacteria into the surrounding environment, and endotoxins, which are toxins "within" the bacterial cell and released only after destruction of the bacterial outer membrane. The toxic activity of LPS was first discovered and termed endotoxin by Richard Friedrich Johannes Pfeiffer. In lower levels and over a longer time period, there is evidence LPS may play an important and harmful role in autoimmunity, obesity, depression, and cellular senescence. In severe cases, LPS can play a role in causing septic shock. LPS is a potent activator of the immune system and pyrogen (agent that causes fever). Lipopolysaccharides can have substantial impacts on human health, primarily through interactions with the immune system. ![]() Today, the term endotoxin is often used synonymously with LPS, although there are a few endotoxins (in the original sense of toxins that are inside the bacterial cell that are released when the cell disintegrates) that are not related to LPS, such as the so-called delta endotoxin proteins produced by Bacillus thuringiensis. They are composed of an O- antigen, an outer core, and an inner core all joined by covalent bonds, and are found in the outer membrane of Gram-negative bacteria. Together, the plasma membrane and the cell wall (outer membrane, peptidoglycan layer, and periplasm) constitute the gram-negative envelope.Lipopolysaccharides ( LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. The periplasm space can act as reservoir for virulence factors and a dynamic flux of macromolecules representing the cell’s metabolic status and its response to environmental factors. It is in fact an integral compartment of the gram-negative cell wall and contains binding proteins for amino acids, sugars, vitamins, iron, and enzymes essential for bacterial nutrition. Sandwiched between the outer membrane and the plasma membrane, a concentrated gel-like matrix (the periplasm) is found in the periplasmic space. The peptidoglycan layer is non-covalently anchored to lipoprotein molecules called Braun’s lipoproteins through their hydrophobic head. It contains structures that help bacteria adhere to animal cells and cause disease. In Gram-negative bacteria the outer membrane is usually thought of as part of the outer leaflet of the membrane structure and is relatively permeable. The LPS molecule is toxic and is classified as an endotoxin that elicits a strong immune response when the bacteria infect animals. The outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS) in addition to proteins and phospholipids. The Gram-negative’s cell wall is thinner (10 nanometers thick) and less compact than that of Gram-positive bacteria, but remains strong, tough, and elastic to give them shape and protect them against extreme environmental conditions. ![]() The safranin is responsible for the red or pink color seen with a gram-negative bacteria. The gram-negative bacteria do not retain crystal violet but are able to retain a counterstain, commonly safranin, which is added after the crystal violet. In the Gram-negative Bacteria the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane. Figure: Structure of Gram-negative cell wall: Gram-negative outer membrane composed of lipopolysaccharides. The Gram-negative cell wall is composed of an outer membrane, a peptidoglygan layer, and a periplasm. Recognize the characteristics of a gram-negative bacteria. ![]()
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