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10 Cards in this Set
- Front
- Back
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Which mycobacterial species resembles a shepherd's crook?
A. Mycobacterium tuberculosis B. Mycobacterium marinum C. Mycobacterium gordonae D. Mycobacterium kansasii E. Mycobacterium avium-intracellulare |
D. M.
M. kansasii is a photochromagen-producing species, Group I by the Runyon classification system for non-tuberculous Mycobacteria. QCCP2, Mycobacteria |
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Which of the following features identifies a mycobacterial stain as presumptive M. tuberculosis?
A. positive acid-fast staining with cording in broth culture B. NAP-sensitivity of broth-grown mycobacteria C. arylsulfatase positivity D. A & B E. A, B, C |
D. A & B.
Cording refers to the ability of Mycobacterium tuberculosis to clump when cultured, resulting in strings or cords of organisms, a feature due to cord factor - a virulence factor. Also, NAP-sensitivity is a suspicious finding that is consistent with M. tuberculosis. Arylsulfatase is used to separate fast-growing Mycobacterium between the positive M. fortuitum and M. chelonei, and the nonpathogenic and arylsulfatase-negative M. phlei and M. smegmatis. QCCP2, Mycobacteria |
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Which of the following slow-growing Mycobacterium accumulates niacin?
A. M. tuberculosis B. M. bovis C. M. africanum D. M. avium-intracellulare E. M. kansasii |
A. M.
Of all the known major species of Mycobacteria, only M. tuberculosis, M. simiae, and to a lesser extent, and M marinum, are able to accumulate niacin as demonstrated with a yellow colony on media with a detection compound (cyanogen chloride) that reacts with the free niacin. QCCP2, Mycobacteria |
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To which of the Runyon classification groups does M. tuberculosis belong?
A. Group I B. Group II C. Group III D. Group IV E. none of the above |
E. none of the above.
The Runyon classification system is expressly used for the classification of non-tuberculous mycobacteria. Group I is the photochromagens (yellow pigment when grown in the light), including Mycobacterium kansasii, M. simiae, M. marinum, and M. asiaticum, lending itself to the mnemonic, “SMAK the photographer.” Group II is scotochromagens, that is, they make pigment in the dark and include M. gordonae, M. scrofulaceum, M. thermoresistable, and M. flavescens. (They get in “FiGhTS” in the dark). Group III is the non-pigmented, and includes M. avium-intracellulare, M. hemophilium, M. terratriviale, M. malmoense, M. gastri, M. bovis, M. xenopii. Finally, Group IV is the fast growers and the only significant organisms to human infections in this group are M. chelonei and M. fortuitum. QCCP2, Mycobacteria |
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Which of the following Mycobacterium species, although technically a Runyon Group II, could also be considered a Class I organism under certain conditions?
A. M. kansasii B. M. szulgai C. M. scrofulaceum D. M. gordonii E. M. thermoresistible |
B. M .
M. szulgai is a scotochromagen at 35°-37°C and a photochromagen at 25°C. QCCP2, Mycobacteria |
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What percentage of immunocompetent people infected with primary TB infection develop active TB?
A. 0% B. 10% C. 50% D. 90% E. 100% |
B. 10%.
Actually, 10% is on the high side of estimates as the vast majority of people (90%) infected with respiratory TB resolve the infection. The remaining 5-10% (higher in the immunocompromised) go on to develop active disease, which most often is pulmonary, but can also be extrapulmonary. QCCP2, M. tuberculosis |
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Which of the following coinfections often lead to smear-negative TB and PPD anergic false-negative results?
A. HCV B. Borrelia burgdorfei C. Ascaris lumbricoides D. HIV E. methicillin-resistant Staphylococcus aureus |
D. HIV.
TB is a difficult disease to diagnose - screening tests like PPC and sputum smears have high false-negative rates and culture often takes weeks. Nucleic acid amplification tests may be more sensitive and rapid, but long-term validation is lacking. HIV makes diagnosis even more difficult. QCCP2, M. tuberculosis |
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What condition particularly predisposes toward M. kansasii pulmonary disease?
A. pneumoconiosis B. pre-existing M. tuberculosis C. squamous cell carcinoma of the lung D. diabetes mellitus E. congenital pulmonary adenomatoid malformation |
A. pneumoconiosis.
Behind Mybacterium tuberculosis and M. avium-intracellulare, M. kansasii is one of the most common causes of mycobacterial pulmonary disease. QCCP2, Mycobacteria |
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Which of the following mycobacterial species is the cause of the Buruli ulcer?
A. M. leprae B. M. ulcerans C. M. fortuitum D. M. marinum E. M. chelonei |
B. M.
The necrotizing ulcerative cutaneous Buruli ulcer is caused by infection with M. ulcerans. All the choices are notable for causing skin disease without pulmonary disease. Most are associated with penetrating trauma - M. marinum with fresh water fish tanks. QCCP2, Mycobacteria causing skin and soft tissue infections |
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Which of the following features are associated with lepromatous leprosy?
A. widespread skin infections B. superinfection with Strongyloides C. non-caseating granulomas with few AFB D. A & B E. A, B, C |
D. A & B.
Lepromatous leprosy is associated with anergy and therefore a more widespread involvement with the presence of large numbers of acid-fast bacilli and foamymacrophages. The tuberculoid form is associated with a robust granulomatous reaction to infection. In tuberculoid form, there is a small number of organisms present. Two leprosy factoids: Mycobacterium leprae grows on armadillo footpads and the most consistent signs are anesthetic skin lesions with palpable prominent peripheral nerves. QCCP2, M. leprae |
