...4. Compare and contrast gram-positive and gram-negative cell walls with regard to (a) sensitivity to antimicrobial agents, (b) resistance to phagocytosis, (c) chemical composition, and (d) decolorization by alcohol. Gram-positive bacteria differ from gram-negative bacteria in the structure of their cell walls. The cell walls of gram-positive bacteria are made up of twenty times as much murein or peptidoglycan than gram-negative bacteria. These complex polymers of sugars and amino acids cross-link and layer the cell wall. The thick outer matrix of peptidoglycan, teichoic acid, polysaccharides, and other proteins serve a number of purposes, including membrane transport regulation, cell expansion, and shape formation. Almost all bacteria can be classified as gram-positive or gram-negative. The classification relies on the positive or negative results from Gram’s staining method, which uses complex purple dye and iodine. Because gram-positive bacteria have more layers of peptidoglycan in their cell walls than gram-negative, they can retain the dye. Both gram-positive and gram-negative bacteria have a cell wall made up of peptidoglycan and a phospholipid bilayer with membrane-spanning proteins. However, gram-negative bacteria have a unique outer membrane, a thinner layer of peptidoglycan, and a periplasmic space between the cell wall and the membrane. In the outer membrane, gram-negative bacteria have lipopolysaccharides (LPS), porin channels, and Murein lipoprotein all of which gram-positive...
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...disease, the pathogen must be isolated from the host and grown in a pure culture, the pathogen in the pure culture must cause the disease when it is inoculated into a healthy lab animal, and finally the pathogen must be isolated from the animal and must be shown to the original organism. Bassi and Pasteur were not able at that time to correlate the pathogen with the specific disease. Question 3: In 1884, Hans Christian Gram described a method of staining bacterial cells while not staining surrounding animal tissues; however, he thought the staining method he developed was faulty because not all bacteria stained. In a letter to the editor of the journal in which Gram published his findings, write your response to Gram's concern. Answer 3: Dear Editor, when staining bacteria I first heat the smear and cover with a basic purple dye, after that short time the purple dye is washed off and the smear is then colored with iodine. After the iodine is placed certain cells become purple and some become dark violet. The slide is decolorized to remove the purple from some cells but not from all. Safranin is then applied. Some bacteria were seen until...
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