According to the beginning of Chapter 9, what is germ theory?
Provide an example of a pathogen. What has the pathogen developed to be particularly harmful to other organisms and more beneficial to itself? Explain how these "developments" came about. (Hint: The organisms didn't attain a selective advantage because it wanted it!) What is the bodily response against the pathogen? (elaborate on this...) Is it effective? Are there medical treatments against the pathogen? Why do they work? Are there preventative measures against the pathogen? (Ex. vaccines) Why do they work?
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Carroll explained that the germ theory established that microorganisms are the cause of diseases. Instead of the previous idea that that diseases were caused by spontaneous generation, Louis Pasteur proved that diseases were caused by microbes that “[grew] under the right conditions” (216).
ReplyDeleteAn example of a pathogen would be a virus like the Influenza virus. The influenza virus “can reproduce only in a host cell” (Campbell 330). Because the influenza virus does not have the machinery to reproduce, the virus would infect cells in an organism and utilize the machinery in the cells to create new viruses. The reproduction of the virus relates to the theme of heritable information, which deals with the passing down of genetic data. The viruses utilize the host cell to synthesize nucleic acids to form the viral DNA or RNA which get passed down to the new viruses. The influenza virus in particular has a viral envelope, which is derived from the plasma membrane of the host cells. Because the plasma membrane has the MHC glycoproteins, proteins that “mark body cells as ‘self’ ” (Campbell 907), the virus is not recognized as a foreign invader by lymphocytes and a specific immune response is not initiated. The plasma membrane of the virus better facilitates its reproduction, as the virus can infect other cells while remaining undetected by the leukocytes.
Since the influenza virus is an RNA virus, the virus can experience many mutations to create new “adaptations” (I use this term loosely because a virus is technically not alive). The RNA virus experiences a “high rate of mutation because the replication of [its] nucleic acid does not involve the proofreading of DNA replication” (Campbell 337). As we have learned, mutations may cause a selective advantage (again, this is used loosely) for the virus so the virus could better infect its host. A mutation could have resulted in the virus wrapping itself in the host’s plasma membrane.
In the body, the macrophages and some B cells will engulf the virus and display the viral proteins on its surface. The lymphocyte will form two clones, the effector cells and the memory cells. The memory cells are “long lived cells bearing receptors specific for the same [viral] antigen” (905) which aim to eliminate the viral antigen. Some B and T cells generate plasma cells, which are antibody-producing effector B cells. The plasma cells secrete antibodies, which bind to the epitope of the antigen of the virus. Antibody-mediated agglutination occurs, as the antibody binds to the antigens of several viruses, clumping them together. The clump of viruses are then phagocytosed by macrophages.
Currently, vaccines can help prevent against viruses. The vaccines are “harmless variants or derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen” (Campbell 335). In other words, after the harmless derivation of the virus is injected into the body, the immune system destroys the derivation and ‘remembers’ the derivation the leukocytes destroyed. Because the actual virus is similar to the derivation, the body would remember the protein coat of the virus and more effectively control and destroy the virus, by neutralizing the virus before it could enter target cells for example. Some drugs like AZT interfere with the viral nucleic acid synthesis, inhibiting the reproduction of the new viruses. However, current medical technology is largely lacking when dealing with viruses.
As Carrol hints, Germ theory refers to the idea that microoorganisms cause diseases. For example, germ theory asserts that cholera is caused by enterotoxin producing varieties of Vibrio Cholerae (meant to be in italics for the entire post). Vibrio Cholerae produces the enterotoxin cholera toxin. Cholera toxin causes the mucosal epithelial cells of the small intestine to secrete water into the small intestinal lumen. Thus, the victim experiences exhaustive diarrhea which can lead to dehydration, low blood pressure, and eventually shock. The bacteria of the Vibrio genus that first developed the ability to produce cholera toxin and their offspring were able to quickly move from one host to another since the watery stool of cholera victims can easily mix/flow into drinking water. This allowed Vibrio Cholerae to live in less competitive habitats because the bacteria were continuously moving from infected hosts to "vacant" non-infected hosts. Most other Vibrio genus bacteria could not change feequently move into new hosts or new environments and experienced far ore competetion for food and space than Vibrio Cholerae. Thus with more food and space than normal Vibrio, Vibrio Cholerae had a chance to survive and thus reproduce than other Vibrio strains. A non-specefic defense against Vibrio Cholerae is the gastric juice; Vibrio Cholerae cannot survive the acidity. Vibrio Cholerae produces lipopolysaccharide antigens which elicit a specific immune response from B lymphocytes. However the speed at which cholera toxin effects the mucosal epithelial cells of the small intestine reduce the effectiveness of this immune response in saving the host's life. Preventative measures consist of proper water sanitation methods and are very successful because cholera mainly spreads when stool mixes with the water supply. The principal treatment to this disease is rehydration either orally orr intravenously. Rehydration saves the victim from dehydration as much of the Vibrio Cholerae passes through the stool.Antibiotics like erythromycinare also used to reduce the severity of cholera symptoms by killing Vibrio Cholerae( destroying their cell walls).
ReplyDeleteGerm theory describes how diseases are caused and obtained through microorganisms. The germ theory was proved after Louis Pasteur shouted out that women were getting increasingly sick in hospitals due to "doctors that carry deadly microbes from sick women to healthy ones" (215).
ReplyDeleteMycobacterium tuberculosis (italicized) is the leading cause of tuberculosis. M. tuberculosis is a gram-positive aerobe. It has a cell wall with an extra layer composed of lipids, glycolipids, and polysaccharides. M. tuberculosis can withstand gram stains, so researchers cannot tell that the dangerous bacteria is there by using the gram stain. The bacteria "disrupts the health of the host by invading tissues" (Campbell 541). The bacteria resides in places with high oxygen content, mainly the lungs. Most other mycobacteria aren't harmful. M. tuberculosis has developed a resistance to penicillin because of penicillin's wide use to treat everything. M. tuberculosis has also developed a mutualistic relationship with HIV/AIDS. Because HIV causes a weaker immune system, the body is more vulnerable to tuberculosis.
When M. tuberculosis lives in the lungs, it is engulfed by alveolar macrophages (nonspecific defense) but the bacteria cannot be broken down by lysosomes within the macrophage because it blocks the fusion of phagosomes with lysosomes. Therefore, the macrophage becomes the bacteria's host and the place where the bacteria can divide (one division every 15-20 hours). So the body's nonspecific immune response to the bacterium is unsuccessful and the bacteria can divide in order to prepare for an attack on the human body.
When treated, tuberculosis has a mortality rate of less than 5%. First line drugs for tuberculosis are ethambutol, isoniazid, pyrazinamide, rifampicin, and streptomycin. Drugs are used in combination because of frequent mutations that may cause bacterial resistance to one of the drugs. Treatment must go on for at least six months. These drugs have multiple effects on Mycobacterium tuberculosis. Drugs prevent cell wall synthesis by targeting arabinogalactan, protein synthesis by targeting the ribosomes, cell respiration by targeting mycolic acid, and ATP synthase. Basically, the drugs prevent the duplication and existence of the bacteria.
Tuberculosis is received through airborne bacteria. Washing hands especially when around people with coughs is important. Having a tuberculosis skin test, a chest X-ray (to look for signs of tuberculosis in the lungs), and avoiding too much contact with people who are coughing.