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

3 to 8 weeks of incubation Rapid-growings

> 3 days Non-growing: Mycobacterium leprae

Mycobacterium Most human infections are caused by

M. tuberculosis, M. leprae, M. avium complex, M. kansasii, M. fortuitum, M. chelonae, M. abscessus

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

Mycobacterium tuberculosis/Pathogenesis Virulence

Capable of intracellular growth in unactivated macrophages

Disease primarily from host response to infection

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

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

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

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

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

Laboratory Diagnosis of Mycobacterial Disease Identification

Morphologic properties Biochemical reactions Analysis of cell wall lipids Nucleic acid probes Nucleic acid sequencing