MAHE 2006 Mycobacteria
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- M. avium intracellulare complex
- M. xenopi
- M. scrofulaceum
- M.marinum
Answer:M. avium intracellulare complex
Review:
A Quick Review of the Mycobacteria
All Mycobacteria share the following characteristics:
They are nonmotile, slim rod shaped organisms, 1-10 µm long.
They are obligate aerobes.
They grow very slowly when compared with conventional bacterial such as E. coli. They contain mycolic acid, a rare acid that is otherwise only found in Nocardia and Corynebacterium.
They stain Acid-fast with the Ziehl-Neelson stain.
A Quick Review of M. tuberculosis:
M. tuberculosis is a slender (1-4µm), unencapsulated, strongly acid-fast rod that frequently shows irregular beadingdue to vacuoles and polyphosphate content.
- M. tuberculosis has doubling time of 18 hours.
- M. tuberculosis multiplies intracellularly in phagosome and prevents phagolysosome fusion.
- M. tuberculosis produces large amounts of niacin, however, drug resistant strains can no longer do this.
- M. tuberculosis makes a heat sensitive catalase, unless it is INH resistant.
- M. tuberculosis reduces nitrate. (M. bovis does this too.)
- M. tuberculosis is virulent for Guinea pigs.
The virulence factors of M. tuberculosis include:
Waxes D, a heterogeneous group of peptidoglycolipids in cell wall with adjuvant activity.
Cord factor (Trehalose 6,6 dimycolate) which is a poorly understood determinant of pathogenicity that does manybad things in vitro.
Sulfatides which seem to be involved in the inhibition of phagolysomal fusion.
A Quick Review of the Nontuberculous Mycobacteria
The Nontuberculous Mycobacteria are soil and water organisms
The Nontuberculous Mycobacteria are noncommunicable. (i.e., There is no person to person spread.)
The Nontuberculous Mycobacteria prevents phagosome-lysosome fusion.
Disease usually develops in setting or trama/surgical disruption or immunosuppression.
The Nontuberculous Mycobacteria do not infect guinea pigs.
As a group, the Nontuberculous Mycobacteria are INH resistant. (M. kansasii is the exception to this rule.)
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Runyon Classification System of the Atypical Mycobacteria Runyon I Grown in the Dark.
Runyon I:
Members of Runyon I are slow growing.
Members of Runyon I produce a yellow-orange pigment when exposed to light.
A Few Interesting Facts About Runyon I Organisms:
M. kansasii
- On acid fast stain, M. kansasii appears as a long, banded, beaded, "barber pole", yellow bacillus due to beta carotene crystals.
- Some nonpathogenic strains of M. kansasii are catalase negative.
- M. kansasii reduces nitrate like M. tuberculosis.
- M. kansasii causes a lung disease that clinically resembles TB, especially in those with preexisting lung conditions such as COPD.
- Also males are affected more than females.
M.marinum
- Exposed to Light M. marinum causes swimming pool granulomas, and abscesses (fish fancier’s finger).
- Because M. marinum likes to grow at a lower than core body temperature, it causes disease at the site of abrasions.
- M. marinum inhabits both fresh and salt water, and infects a lot of marine organisms
Runyon II:
Members of Runyon II are slow growing.
Members of Runyon II produce yellow-orange pigment in light or dark.
Few Interesting Facts About Runyon II Organisms:
M. scrofulaceum
- M. scrofulaceum produces scrofula, a granulomatous cervical adenitis, usually in children.
- M. scrofulaceum enters through the oral pharynx and draining lymph nodes.
M. xenopi
- M. xenopi grows poorly at 37oC, but prefers temperatures of 42oC- 45oC.
- M. xenopi is isolated from water, hot and cold taps, and granulomatous lesions in swine
Runyon III
Members of Runyon III are slow growing
Members of Runyon III do not produce pigment.
A Few Interesting Facts About Runyon III Organisms:
M. avium intracellulare complex
M. avium intracellulare complex is often called MAC.
M. avium intracellulare complex is most common NTM infection in AIDS.
M. avium intracellulare complex causes:
- In middle-aged smokers with COPD or bronchiestasis, MAC can cause cough, weight loss, upperlobe x-ray changes, and cavities - all similar to TB.
- Patients with brochiectasis from old TB or cystic fibrosis can develop infiltrates from MAC infection inthe diseased lung areas.
- Non-smoking women over 50 who have a persistent cough and interstitial changes in their right middle lobe or lingula can have MAC infection.
The key to diagnosis is thinking to send sputum for AFB smear and culture. Whereas it used to be thought that these women were simply colonized with MAC, it is nowrealized that 20% will die within 5 years unless treatment is given.
- Scrofula, most common cause of cervical lymphadenitis in children. It must be treated by excision. M. avium intracellulare complex is highly drug resistant.
Runyon IV:
Members of Runyon IV are rapid growing.
They produce colonies in less than 5 days.
Members of Runyon IV do not produce pigment.
The production of arylsulfatase is used to distinguish the clinically significant rapid growers.
Members of Runyon IV have a positive test for iron uptake test
Few Interesting Facts About Runyon IV Organisms:
M. chelonei and M. fortuitum
M. chelonei and M. fortuitum cause infections in the immunocompromised (although disseminated-DZ is rare), and those with prosthetic implants.
Sometimes, M. chelonei and M. fortuitum infections can be traced to contaminated operating equipment (e.g., mammoplasty).
Areas infected by M. chelonei and M. fortuitum include soft tissue, lungs, bone, the CNS, and the eye (keratitis).
M. fortuitum reduces nitrate like M. tuberculosis
Tags: mycobacterium, mycobacteria, tuberculosis
Category: MAHE 2006 MCQs
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