Case Study

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Case Study 21: Pseudomonas aeruginosa
1) The colony morphology of our case study is gram negative bacilli (rod) and can grow on any agar media. The culture is quite unique because it produces mucoid colonies, sometimes with fringed edges, with a blue-green metallic sheen. This metallic sheen is due to the pigment pyocyanin which is produced by the organism. Under ultraviolet light, the colonies fluoresce due to the compound fluorescein also produced by the organism. The odor of the organism is unlike most other organisms because it has a grape, fruit-like scent.

2) Based on the triple sugar iron (TSI) test, this organism does not utilize lactose as an energy source therefore the slant of the TSI test remains red. Additionally, the TSI test shows that the butt of the tube is red, meaning that it is a glucose non-fermenter.

3) This organism has an arsenal of microscopic features that make it quite virulent if it can invade the first line of defense. First off this organism has flagella. The flagella are used to adhere to epithelial cells to which it will infect. The flagella are also responsible for the motility of this organism. This organism also produces many enzymes and toxins to add to its virulence. Exotoxin A is one of the main virulence factors of this organism. This toxin catalyzes ADP-ribosylation and causes the inactivation of elongation factor 2 which negates protein synthesis in the infected cell which ultimately leads to cell death. The next toxin, Exoenzyme S, is also a major virulence factor produced by this organism. This toxin is also like exotoxin A but it mainly does its damage in the lungs of an infected patient by ribosylating GTP-binding proteins such as Ras. LasA elastase, and LasB elastase are also very important in that they destroy elastin in the lungs which would prevent the lungs from expanding and contracting when breathing. Another microscopic characteristic of this organism is its capsule. The capsule is made up of...
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