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10 Cards in this Set
- Front
- Back
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What is Ziehl-Neelsen stain?
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It is the classic acid fast stain, and used to identify organisms that have waxy material(mycolic acids) in their cell walls. Most bacteria that have been stained with carbol-fuchsin can be decolorized by washing with acidic alcohol. However, certain acid fast bacteria retain this stain(carbol-fuchsin) after being washed with acid alcohol. Mycobacterium tuberculosis is a classic agent used for this.
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What is Gram stain?
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It separates bacteria into 2 classifications according to the composition of their cell walls.
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Give an example of Gram staining.
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If a clinical specimen is treated with a solution of crystal violet and then iodine, the bacterial cells will stain purple. If the stained cells are then treated with a solvent, such as alcohol or acetone, G+ organisms retain the stain, whereas G- species lose the stain, becoming colorless. Addition of the counterstain safranin stains the clear, G- bacteria pink or red. Microorganisms that lack cell walls, such as mycoplasma, cannot be identified with the Gram stain.
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Are there any limitations regarding thr Gram stain?
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The number of microorganisms required is relatively high. Visualization with the Gram stain requires greater than 10,000(10/4th power)organisms/ml.
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What is KOH preparation used for?
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Treatment with KOH dissolves host cells and bacteria, sparing fungi. One drop of sputum or skin scraping is treated with 10% KOH, and the specimen is examined for fungal forms.
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The most commonly used selective medium is MacConkey agar. TRUE/FALSE
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TRUE. It supports the growth of most G- rods, esp the enterobacteriaaceae, but inhibits growth of G+ organisms and some fastidious G- bacteria, such as Haemophilus and Neisseria species.
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List 4 types of tests that measure bacterial enzymes with regard to identification.
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1. Catalase
2. Oxidase 3. Urease 4. Coagulase |
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What is the Urease test used for/
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The enzyme urease hydrolyzes urea to ammonia and CO2(NH2CONH2 + H2O --- 2NH3 + CO2). The ammonia produced can be can be detected with pH indicators that change color in response to the increased alkalinity. It helps to identify certain species of Enterobacteriacaea, Corynebacterium and helicobacter pylori.
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What is the catalase test?
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The enzyme catalase catalyzes the degradation of H2O2 to water and molecular O2(H2O2----H2O + O2). Catalase positive organisms rapidly produce bubbles when exposed to a solution containg H2O2. This test is key in differentiating between many G+ organisms, e.g., staphylococci are catalase positive whereas strep and enterococci are catalase negative.
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What is the capsular swelling reaction/
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Some bacteria having capsules can be identified directly in clinical specimens by a swelling reaction that occurs when the organisms are treated with serum containing specific antibodies(Quellung reaction) can be used for all serotypes of S. pneumoniae, H. influenzae type b and neisseria meningitidis groups A and C.
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