Mycobacterium tuberculosis and
Mycobacterium leprae
Prepared bySamira Fattah
Assis. Lec.College of health sciences-HMU
Lab 10
Mycobacterium
• A large family of bacteria that have unusually waxy cell walls that are resistant to digestion.
• The mycobacteria have two significant pathogenic species:
- Mycobacterium tuberculosis
-Mycobacterium leprae
M. tuberculosis - causes tuberculosis.
M. leprae - causes leprosy.That affect superficial tissues, especially the skin and peripheral nerves.
General character
•slightly curved or straight rods•Obligate aerobe•Non-motile•Do not form capsule •Slow generation time: 15-20 hours •Lipid rich cell wall contains mycolic acid:
•Responsible for retaining acidic stains
Mycobacterium tuberculosis
Laboratory diagnosis
Specimen:• Fresh sputum• Gastric wash• pleural fluid• cerebrospinal fluid• urine• Biopsy material
Microscopy
smears stained by the Ziehl-Neelsen method.
M. tuberculosis in urineM. tuberculosis in sputum
• sputum is the most commonly tested sample for M. tuberculosis.
• The detection of acid-fast bacilli (AFB) in stained sputum smears examined microscopically is the easiest and quickest procedure, and provides the physician with a preliminary confirmation of a TB diagnosis.
• It also gives a quantitative estimation of the number of bacilli being excreted, which makes it important clinically and epidemiologically for assessing the patient's infectiousness.
2.Culturing on egg-based media• Lowenstein-Jensen
medium -Most commonly used
media for primary isolation of M. tuberculosis.
- colonies are small and buff colored.
- It takes 4-6 weeks to get visual colonies.
3.Tuberculin Skin Test• A tuberculin skin test is done to see if the
person have ever had tuberculosis .
disadvantage • A tuberculin skin test cannot tell how long
person have been infected with TB. It also cannot tell if the infection is latent (inactive) or is active and can be passed to others.
procedure• The test is done by putting a small amount
of TB protein (antigens) under the top layer of skin on inner forearm. If the patient have ever been exposed to the TB bacteria , the skin will react to the antigens by developing a firm red bump at the site within 2 days.
4.Direct detection by using nucleic acid amplification (NAA) test
this test can reliably detect M. tuberculosis bacteria in specimens in hours as compared to weeks for culture.
Mycobacterium leprae
• Mycobacterium leprae has the same shape and size as mycobacterium tuberculosis.
• Mycobacterium leprae is an intracellular bacterium, infecting nerve, skin and mucosal cells
Mycobacterium leprae
• has the longest doubling time of all known bacteria (13-15 days) which makes doing laboratory research (in vitro) on this organism quite difficult.
• unable to be cultured on artificial media because it is obligate intracellular mycobacterium.
Lab diagnosis
M. leprae is detected from the:• tissue fluid • pathological tissue of the lesion
1. Ziehl-neelsen stain• It occurs in large numbers in the lesions• intracellular clumps or in groups of bacilli side by side.
2.Lepromin skin test• to classify the stage of leprosy based on the lepromin
reaction Procedur:• A sample of inactivated (unable to cause infection)
leprosy-causing bacteria is injected just under the skin, usually on the forearm.
• The injection site is labeled and examined 3 days, and again 28 days, later to see if there is a reaction.
3.PCR amplification• using PCR amplification is to verify the
presence of DNA specific to M. leprae.
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