 Wysłany: Czw 6:03, 31 Mar 2011 Temat postu: Puma Espera Bacterial Exotoxins an Puma Espera Sho |
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| For more information on bacterial pathogenicity, see the Suite101 article "How Bacteria Infect the Body and Cause Disease."
There are three main subtypes of bacterial exotoxin: Read on Fimbriae and Bacterial Virulence Gram Negative ( Gram- ) Bacteria Gram Negative Bacterial Stain Many exotoxins are enzymes, which work to catalyze very specific biochemical reactions. As enzymes, these chemicals are reusable. Small amounts are highly toxic because they can be used over and over, causing great harm to the host’s cells. Diseases caused by bacteria that produce exotoxins typically result from these small amounts of toxin, rather than from the presence of the bacteria themselves. Enterotoxins: Damage the lining of the GI tract.Neurotoxins: Interfere with the function of nerves.Cytotoxins: Kill or disrupt the proper functioning of the cells of the host.Disease and Exotoxins Botulism, tetanus and gas gangrene are caused specifically by members of the genus Clostridium, pathogenic bacteria able to produce very potent toxins. Clostridium botulinum, for example, produces the botulinum neurotoxin, responsible for deadly botulism. This same toxin, in minute doses, is used as Botox to prevent formation of wrinkles by paralyzing facial muscles. The lipid-A endotoxin is part of the Gram-negative cell, and, although lipid-A is not nearly as toxic as exotoxins are, high concentrations can cause problems in the host when Gram-negative bacterial cells die or are digested by phagocytic cells of the immune system. Lipid-A in the host can trigger a wide range of symptoms, including fever, inflammation, blood clotting, hemorrhaging and even shock. Bauman, R. (2007) Microbiology with Dise Bacterial Endotoxins Botulism, tetanus, gas gangrene, diphtheria, c***** Puma Espera Shoes, plague and some types of food poisoning are examples of diseases caused by bacterial exotoxins. Toxoid vaccines can expose the body to altered versions of toxins that are not harmful, but help initiate an immune response in advance, so that if infection does occur in the future, the body can produce antitoxic antibodies more quickly. Types of Bacterial Exotoxins Sources Bacteria are divided into two basic groups, Gram-positive and Gram-negative, based on their cell wall characteristics. Gram-negative bacteria have a membrane on their outer cell wall which contains lipopolysaccharide molecules, each with an endotoxin lipid portion called lipid A. The Immune System and Exotoxins Bacterial toxins cause damage either directly, by destroying tissue, or indirectly, by triggering a harmful level of immune response in the host. Toxins act at the site of infection, but can also be transported to other areas of the body via the bloodstream, a condition caused toxemia. Bacterial toxins fall into two general categories based on their position relative to the cell that produces them; exotoxins, which are secreted by bacteria, and endotoxins, which are part of the Gram-negative bacterial cell structure. Exotoxins are proteins produced by some bacteria (both Gram-positive and Gram-negative) as metabolic products that are secreted into the environment or released when the cell dies. These chemicals are highly toxic Puma Espera, and even in small doses can destroy cells of the infected host. To some extent, the body is able to defend itself from exotoxins. The immune system produces antibodies that can neutralize these toxins Puma Clyde Sneakers, but this type of immune response takes time to develop once the body is exposed to a particular toxin; so critical damage may occur before the immune system is able to respond. |
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