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level: Acid Fast Bacilli and Filamentous

Questions and Answers List

level questions: Acid Fast Bacilli and Filamentous

Question	Answer
Slow-growing, aerobic rods with a lipid-rich cell wall that makes them acid fast (Mycolic acid in cell wall resists acid decolorization). A. Cell wall components 60 species, 40 pathogenic to humans M.Tuberculosis and M.Leprae	Mycobacteria
Stain-hot method Mycobacteria appear red (carbol-fuchsin) while other microbes, tissue appear blue (methylene blue)	Ziehl-Neelson (ZN)
Growth medium specially used for culture of Mycobacterium species. When grown on LJ medium, M. tuberculosis appears as brown, granular colonies sometimes called "buff, rough and tough"	Lowenstein Jensen medium
Acid fast, aerobic Spread by droplets of infected ppl (coughing) 10% will develop disease. Slow growing on Lowenstein Jensen medium (6 weeks) Produces a heat-sensitive catalase (a standard catalase test at 68oC is negative; active at body temperature) Diagnosis: PPD skin test (Mantoux) measure, ZN stain, chest X-ray	M.Tuberculosis
Slow-growing [>7 days] 1. Photochromogens, produce yellow-orange pigment when exposed to light 2. Scotochromogens, produce yellow-orange pigment regardless of light 3. Nonpigmented 4. Rapidly growing [<7 days]	Runyon Classification
Causes leprosy (Hansen's disease) No culture in vitro, on footpads of mice and armadillos Acid fast rods, obligate intracellular; optimal growth is at cooler parts of the body (skin, mucous membranes, and peripheral nerves) Spread by droplets, prolonged exposure Incubation period 2-10 years, 10% develop disease Tuberculoid leprosy and lepromatous leprosy	Mycobacterium Leprae
– High resistance – Nerves damaged – Loss of terminal phalanges – Few microbes	Tuberculoid leprosy
- Low resistance – Nerves, skin, eyes, nose, mouth etc. damaged – Bacteremia • liver, spleen, BM involved	Lepromatous leprosy
Strictly aerobic, gram +ve rods, catalase +ve Stain weakly Acid-Fast (due to mycolic acids in the cell wall) Found in the soil Not part of the human normal flora Two species are pathogenic for humans: Nocardia asteroides [Worldwide] and Nocardia brasiliensis [Central America] Form thin filaments (confused with fungus) Can grow on most non-selective media (slow, 3-5 days)	Nocardia
Presence of aerial hyphae and acid fastness	How to test for its Nocardia's presumptive identification?
Nocardia	Gram stain of which bacteria?
Gram +ve rods, facultative/strictly anaerobes Not acid fast but similar to nocarida Grow slowly Develop thin branching filaments similar to fungi No mitochondria (prokaryotic bacteria sensitive to penicillin) low virulence No person to person transmission Actinomycosis - virulent in humans	Actinomyces
Virulence of actinomyces Usually Actinomyces israelli (which is part of normal oral flora, not known what causes them to become virulent) Most infections are cervicofacial (poor oral health) Should be expected if: - Tissue swelling with fibrosis - Scaring - Draining sinus along the angle of the jaw and neck	Actinomycosis