ACTIVITY 12 1. Differentiate bacterial infection from bacterial intoxication. Infection refers to a condition caused by the bacteria themselves. intoxication is the result of the waste products the bacterium release 2. What are the effects of the conditions above? Specify the symptoms. BACTERIAL INFECTION: Bacterial infections are illnesses that occur when harmful forms of bacteria multiply inside the body. They range from mild to severe. Although they include such deadly diseases as plague, tuberculosis, and cholera, these and many other bacterial infections can be prevented by good sanitation or cured by antibiotics. There are many common symptoms of a bacterial infection. A common example is a fever. When the body attempts to fight infections on its own, it is common for its temperature to spike. A low-grade fever (less than 102 degrees) may go unnoticed in adults, but a high fever can make you feel worse than the actual infection. An upset stomach is another common symptom of a fever in someone exposed to salmonella or other food borne bacteria. Other digestive problems that may indicate a bacterial infection include black, tarry or bloody stools; diarrhea; and loss of bowel control. A bacterial infection can also lead to swollen lymph nodes. These are under the arms, at the base of the skull, the back of the neck and other areas through the body. The lymph nodes swell in their attempt to clear the body of bacteria. Headaches are another common symptom. While the headache is often a low grade, annoying pain, if the pain is severe or makes it difficult to think, eat or keep your eyes open, visit the doctor immediately. BACTERIAL INTOXICATION: This type of food poisoning intoxication can occur when the food eaten is contaminated with toxins (poison) or toxin producing bacteria. The bacteria multiply in the food and by-product of this multiplication is toxin, the poison that causes illness. The toxin producing bacteria can multiply in the food or in the body and not all toxins are destroyed by cooking.The most common symptom od this intoxication is vomiting. As toxin enters into human body system, the body realizes that that is not good for it and vomits the poison out.Bacterial intoxication will typically have shorter incubation period than infection (with sudden onset), which usually only lasts one day and fever is rarely present. 3. Briefly explain the mechanism of infection by the following microorganisms in the digestive tract A. Vibrio cholera When the surviving bacteria exit the stomach and reach the small intestine, they need to propel themselves through the thick mucus that lines the small intestine to get to the intestinal walls, where they can thrive. V. cholerae bacteria begin production of the hollow cylindrical protein flagellin to make flagella. These flagella are cork-screw helical fibers that rotate to propel the bacteria through the mucus of the small intestine. B. Shigella dysenteriae Each specific pathogen has its own mechanism or pathogenesis, but in general the result is damage to the intestinal lining, leading to the inflammatory immune response. This can cause elevated temperature, painful spasms of the intestinal muscles (cramping), swelling due to water leaking from capillaries of the intestine (edema), and further tissue damage by the body's immune cells and the chemicals, called cytokines, which are released to fight the infection. The result can be impaired nutrient absorption, excessive water and mineral loss through the stools due to breakdown of the
control mechanisms in the intestinal tissue that normally remove water from the stools, and in severe cases the entry of pathogenic organisms into the bloodstream. Some microorganisms – for example, bacteria of the genus Shigella – secrete substances known as cytotoxins, which kill and damage intestinal tissue on contact. Viruses directly attack the intestinal cells, taking over their metabolic machinery to make copies of themselves, which leads to cell death. C. Salmonella typhi The toxin acts on the lining of the blood vessels, the vascular endothelium. The B subunits of the toxin bind to a component of the cell membrane known as Gb3 and the complex enters the cell. When the protein is inside the cell, the A subunit interacts with the ribosomes to inactivate them. The A subunit of Shiga toxin is an N-glycosidase that modifies the RNA component of the ribosome to inactivate it and so bring a halt to protein synthesis leading to the death of the cell. The vascular endothelium has to continually renew itself, so this killing of cells leads to a breakdown of the lining and to hemorrhage. The first response is commonly a bloody diarrhea. This is because Shiga toxin is usually taken in with contaminated food or water. D. Escherichia coli EPEC induce a profuse watery, sometimes bloody, diarrhea. They are a leading cause of infantile diarrhea in developing countries. Outbreaks have been linked to the consumption of contaminated drinking water as well as some meat products. Pathogenesis of EPEC involves a plasmid-encoded protein referred to as EPEC adherence factor (EAF) that enables localized adherence of bacteria to intestinal cells and a non fimbrial adhesin designated intimin, which is an outer membrane protein that mediates the final stages of adherence. They do not produce ST or LT toxins. Adherence of EPEC strains to the intestinal mucosa is a very complicated process and produces dramatic effects in the ultrastructure of the cells resulting in rearrangements of actin in the vicinity of adherent bacteria. The phenomenon is sometimes called "attachment and effacing" of cells. EPEC strains are said to be "moderately-invasive", meaning they are not as invasive as Shigella, and unlike ETEC or EAEC, they cause an inflammatory response. The diarrhea and other symptoms of EPEC infections probably are caused by bacterial invasion of host cells and interference with normal cellular signal transduction, rather than by production of toxins.
REFERENCE
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