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Mycobacterium

Mycobacterium. Nonmotile Non-spore-forming Aerobic bacilli Cell wall rich in lipids Hydrofobic surface resistant to many disinfectants & stains resistant to decolorizing “acid-fast bacilli” Grow slowly (every 12-24 h). Mycobacterium. Slow-growings

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Mycobacterium

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  1. Mycobacterium • Nonmotile • Non-spore-forming • Aerobic bacilli • Cell wall rich in lipids • Hydrofobic surface resistant to many disinfectants & stains resistant to decolorizing “acid-fast bacilli” • Grow slowly (every 12-24 h)

  2. Mycobacterium • Slow-growings • 3 to 8 weeks of incubation • Rapid-growings • > 3 days • Non-growing: Mycobacterium leprae

  3. Mycobacterium • Most human infections are caused by • M. tuberculosis, • M. leprae, • M. avium complex, • M. kansasii, • M. fortuitum, • M. chelonae, • M. abscessus

  4. Mycobacterium/Physiology & structure • Cell wall rich in lipids • resistant to many disinfectants & stains • resistant to decolorizing • resistant to antibiotics • antigenic • clumping or chord formation • Classification • Runyon’s

  5. Mycobacterium tuberculosis/Pathogenesis • Virulence • Capable of intracellular growth in unactivated macrophages • Disease primarily from host response to infection

  6. Mycobacterium tuberculosis/Clinical disease • Can involve any organ • Primary infection is pulmonary • In immunocompetant patients replication cease in 3-6 weeks after exposure • 5 % of patients progress to active disease in2 ys. • Another 5-10 %, sometimes later in the life

  7. Mycobacterium tuberculosis/Diagnosis • Clinical diagnosis + • Radiographic evidence of pulmonary disease • Positive skin test reactivity • The laboratory detection of mycobacteria either with microscopy or in cultures

  8. Mycobacterium leprae • Weakly Gram-positive, strongly acid-fast bacilli • Unable to be cultured on artificial media • Diagnosis made with specific skin test or acid-fast stain • Capable of intracellular growth • Disease: tuberculoid-lepromatous-intermediate forms

  9. Mycobacterium avium Complex • In environment: • Water(fresh, brackish,ocean, drinking water) • Soil • Before AIDS epidemic • Transient colonizer in asymptomatic patients • Disease in patients with compromised pulmonary function • With AIDS, a new spectrum of disease • “The most common mycobacterial disease” • disseminated

  10. Laboratory Diagnosis of Mycobacterial Disease • Detection • Skin test • Microscopy • Carbolfuchsin acid-fast stain • Fluorochrome acid-fast stain • Culture • Solid agar-based or egg-based media • Broth-based media

  11. Laboratory Diagnosis of Mycobacterial Disease • Identification • Morphologic properties • Biochemical reactions • Analysis of cell wall lipids • Nucleic acid probes • Nucleic acid sequencing

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