Exam 1 – Microbiology Definitions – Flashcards
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| How is Tuberculosis transmitted? |
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| Droplet Nuclei via coughing, highly communicable |
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| How is the tuberculosis primary infection acquired? |
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| the person inhales the organisms and they multiply in the alveolar macrophages unaffected by the immune system Hypersensitivity and cell-mediated immunity develop in 2-6 weeks |
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| What are the typical symptoms of tuberculosis? |
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| development of a tuberule (microscopic granuloma) in the lung |
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| What is reactive tuberculosis? |
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| occurs in the lung apex via formation of pulmonary cavities |
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| What is the pathogenesis of tuberculosis |
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| chronic fever, weight loss, night sweats, blood cough along with an extra-pulmonary disease (dissemination to bones and CNS) |
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| How is tuberculosis diagnosed? |
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| skin test (PPD) which measured delayed-type hypersensitivity to tuberculoprotein. Tuberculosis can also be diagnosed by serodiagnosis in which the cell-mediated immune response is measured in whole blood samples inoculated with mycobacterial antigens |
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| What is the treatment for tuberculosis? |
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| combined prolonged drug therapy to prevent resistance (Isoniazid, Rifampin, Ethamtubol and Pyrazinamide), treatment must be directly observed therapy (watch the patient take his drugs) |
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| What is the clinical significance of NTM? |
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| bacteria can cause non-communicable chronic pulmonary diseases, disseminated diseases and cutaneous infections. |
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| What are the unique characteristics of mycobacteria |
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| growth rate and recovery time and pigment production in relation to light |
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| What are the 7 safety precautions to be followed while working in a mycobacteria laboratory? |
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| (1) negative pressure room (2) biological safety cabinet (3) face mask (4) safety cups for centrifugation (5) splash-proof discard containers (6) disposable loops/needles and (7) proper disposal of waste |
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| What is used to digest mycobacteria for processing? |
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| NALC- N-acetyl-L-cysteine |
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| What is used to decontaminate mycobacteria for processing? |
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| Sodium hydroxide or benzalkonium chloride and oxalic acid |
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| What is used to concentrate mycobacteria for processing? |
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| centrifuge |
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| What is used to stop the decontaminate process? |
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| phosphate buffer |
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| Why do you need to digest, decontaminate and concentrate mycobacteria specimens? |
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| specimen when plated with be overgrown with normal flora. |
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| What is the procedure of the auramine-rhodamine fluorochrome stain? |
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| heat fix the slides then flood with auramine-rhodamine fir 15-20 minutes, rinse with DI water, decolorized with 0.5% acid-alcohol for 2-3 minutes, rinse with DI water, flood with potassium permanganate for 2-4 minutes, rinse and allow to dry |
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| What are the advantages to the auramine-rhodamine stain? |
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| Detection is enhanced against a dark background and the slide can be viewed at a lower magnification allowing for visualization of more fields at one time. Another advantage is that you can re-stain with ziehl-nelson to confirm right on the same slide, you do not need a fresh slide |
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| What are the disadvantages to the auramine-rhodamine stain? |
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| rapid growers do not always appear fluorescent and you need to confirm with a ziehl- nelson stain. The stained bacteria can also float into the oil and off the slide yielding a false negative |
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| What is the procedure for the Ziehl-neelsen stain? |
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| heat fix the smear to the slide, flood the slide with carbol fuchsin stain and steam the slides for 1 minute, keep stain on slides for 4-5 minutes, rinse, decolorize with 3% acid-alcohol, rinse, flood with methylene blue for 1 minute, rinse, and let dry. Red is positive for ziehl-neelsen |
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| What is the procedure for the kinyoun stain? |
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| The procedure is heat fix the slide, flood with carbol fuchsin for 5 minutes, rinse, decolorize with 3% acid- alcohol, rinse, and flood with methylene blue for 1-3 minutes, rinse, let dry. |
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| What is the Runyon classification? |
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| based on growth and pigment production and is used for NTM |
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| What are schotochromogens? |
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| develop pigment in the dark or the light |
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| Examples of schotochromogens |
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| M. scrofulaceum and M. gordonae |
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| What are photochromogens? |
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| form pigment following exposure to light after being grown in the dark |
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| examples of photochromogens? |
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| M. kansasii, and M. marinum |
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| What are nonphotochromogens? |
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| nonpigmented whether grown in light or dark |
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| examples of nonphotochromogens? |
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| M. avium-intracellulare (MAC, MAI) |
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| Egg-based solid medias |
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| Lowenstein-Jensen (inhibits normal flora), Lowenstein-Jensen Gruft modification (added antibiotics) or mycobactosel (antibiotics) |
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| Serum/agar based solid medias |
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| middlebrook 7H10/7H11 |
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| liquid media |
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| Middlebrook |
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| The arylsulfatase test principle |
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| used to identify potentially pathogenic rapid growers, The enzyme arylsulfatase is present in some mycobacteria and the test is used to determine how fast the bacteria can break down phenolphthaliein disulfate into phenolphthalein which forms a pink color in the presence of sodium bicarbonate. |
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| Which bacteria are arylsulfatase positive? |
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| M. fortuitum and M. chelonae and slow-growing M. marinum and M. szulgai (14 days) |
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| The catalase test principle |
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| Most mycobacteria produce catalase which can split hydrogen peroxide into water and oxygen. The test can be used semi-quantitatively in that if the bacteria can produce 45 mm of bubbles in a test tube is in one group of mycobacteria and if it cannot it is another group. The ability of the catalase enzyme to remain active after heating also separates mycobacteria |
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| Which bacteria are catalase negative? |
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| M. tuberculosis, M. bovis, M. gastri and M. haemophilum |
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| The iron uptake test principle |
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| utilized to identify rapidly growing mycobacteria capable of converting ferric ammonium citrate to an iron oxide. An LJ slant is inoculated with the organism incubated until visible growth develops, aqueous ferric ammonium citrate added, and the slant incubated for up to 21 days at 37°C. Positive is reddish brown color in the colonies indicates production of iron oxide and Negative shows no color change. |
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| The niacin accumulation test |
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| bacterium lacks the enzyme necessary to convert niacin to another metabolite in the coenzyme pathway. A positive test is yellow, a negative is clear liquid. |
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| Which bacteria is niacin accumulation positive? |
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| M. tuberculosis |
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| The nitrate reduction test principle |
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| The presence of nitrate is detected by production of a red colored product on the addition of several reagents. Development of a pink-red color indicates the presence of nitrite, demonstrating the ability of the organism to reduce nitrate to nitrite. If there is no color then the organism cannot reduce nitrite |
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| Which bacteria is nitrate reduction positive? |
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| M. tuberculosis, M. kansasii, M. szulgai and M. fortuitum |
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| Tween 80 hydrolysis test principle |
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| detect lipase that is able to hydrolyze Tween 80 into oleic acid and polyoxyethyated sorbitol |
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| Which bacteria are tween 80 hydrolysis positive? |
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| Mycobacteria that are positive for Tween 80 hydrolysis are non-pathogenic, slow-growing scotochromogens and nonphotochromogens |
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| Tellurite reduction test principle |
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| detect species that can reduce potassium tellurite at variable rates. If the bacteria can reduce potassium tellurite in 3-4 days, it is M. avium complex. All rapid-growers reduce tellurite in 3 days. |
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| Inhibition of TCH test principle |
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| used to distinguish M. bovis from M. tuberculosis because M. bovis cannot grow in the presence of TCH. |
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| The molecular methods used to identify mycobacteria |
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| DNA hybridization, amplification with reserve hybridization, amplification and restriction enzyme analysis or DNA sequencing and DNA microarrays. |
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| Susceptibility testing methods for M. tuberculosis |
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| The proportion method uses standardized inoculums (100-300 colonies) to inoculate the agar-based media which contains antibiotics. It is incubated for 3 weeks and if more than 1% of the inoculums survive it indicated resistance. There is broth based susceptibility testing which take 5 days and probes for resistance genes |
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| Susceptibility testing methods for NTM |
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| MIC methods with aminoglycosides and sulfonamides. |
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| How do you process a sterile specimen? |
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| centrifuge and use sediment, screen by AFB smear and inoculate one liquid media and one solid media. |
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| How do you process a non-sterile specimen? |
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| Liquefaction (NALC), decontamination (NaOH), neutralization (buffer or water), centrifugation, screen by AFB smear and inoculate one liquid media and one solid media. |
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| What is the tuberculin skin test? |
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| used to measure delayed-type hypersensitivity to tuberculoprotein (PPD). A positive test indicates that the person was once infected at some time with M. tuberculosis or cross-reacting strain. The value of the test depends on the incidence of primary infections. |
