lab diagnosis of Mycobacterium tuberculosis and M. leprae

1. Mycobacterium tuberculosis
and
Mycobacterium leprae
Prepared by
Samira Fattah
Assis. Lec.
College of health sciences-HMU
Lab 10

2. 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

3. M. tuberculosis -
causes tuberculosis.
M. leprae -
causes leprosy.
That affect superficial
tissues, especially the
skin and peripheral
nerves.

4. 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

5. Mycobacterium tuberculosis

6. Laboratory diagnosis
Specimen:
• Fresh sputum
• Gastric wash
• pleural fluid
• cerebrospinal fluid
• urine
• Biopsy material

7. Microscopy
smears stained by the Ziehl-Neelsen method.
M. tuberculosis in urineM. tuberculosis in sputum

8. • 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.

9. 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.

10. 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.

11. 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.

12. Mycobacterium leprae

13. • 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

14. • 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.

15. Lab diagnosis
M. leprae is detected from the:
• tissue fluid
• pathological tissue of the lesion

16. 1. Ziehl-neelsen stain
• It occurs in large numbers in the lesions
• intracellular clumps or in groups of bacilli side by side.

17. 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.

18. 3.PCR amplification
• using PCR amplification is to verify the
presence of DNA specific to M. leprae.