4. 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 h)

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

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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. 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

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