Mycobacteria - Prac. Microbiology


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Mycobacteria - Prac. Microbiology

  2. 2. Characters • Acid-alcohol fastness • Slow rate of growth
  3. 3. Members of the Genus Mycobacterium 1. Mycobacterium tuberculosis Complex: M. tuberculosis, M. bovis, M. africanum & M. microti. 2. Non-tuberculous mycobacteria (NTM): e.g. M. avium complex & M. fortuitum. 3. Mycobacterium leprae: causes leprosy. 4.The Bacillus of Calmette-Guerin (BCG)
  4. 4. Mycobacterium Tuberculosis Morphology: - Acid-alcohol-fast bacillus - Slender - Straight or curved - Arranged singly or in small groups - Ziehl-Neelsen (Z-N) --- pink in a blue background.
  5. 5. Lipid-Rich Cell Wall Gram Stain
  6. 6. Ziehl-Neelsen (Z-N) Stain • Carbol-fuchsin dye • Heat • Acid-alcohol (decolourization) • Methylene blue • Acid-fast = Mycobacteria
  7. 7. Cultural Characters Media include: - Lowenstein-Jensen (L-J) medium - Middlebrook's medium
  8. 8. Cultural Characters • Strict aerobe (5 - 10% CO2 stimulates its growth). • Colonies appear after 2-4 weeks of incubation at 37°C and may be delayed to 8 weeks.
  9. 9. Human Tuberculosis Mode of Infection Inhalation of droplet nuclei from a patient with open pulmonary tuberculosis. Ingestion of milk contaminated with M. bovis. TB may affect other systems (e.g. TB meningitis, lymphadenitis, renal, genital & intestinal TB).
  10. 10. Oral mainfestations of tuberculosis 1. Primary complex 2. Oral ulceration secondary to pulmonary tuberculosis 3. Lupus vulgaris 4. Tuberculous periapical infection and osteomyelitis.
  11. 11. Laboratory Diagnosis of Open Pulmonary TB Specimens: include sputum, BAL Early morning sputum specimens collected on 3 consecutive days, from a deep productive cough, give the best results
  12. 12. Direct Detection: 1. Smears: Ziehl-Neelsen (Z-N). Under the ordinary light microscope, AFB appear pink in a blue background.
  13. 13. 2. Molecular tests: • For rapid detection • Expensive
  14. 14. Cultivation: Conventional culture media: (incubated in 5 – 10% CO2 at 37o C): L-J tube - Results may be relatively delayed (2-8 weeks).
  15. 15. Fluid Medium Systems (4-14 days identification) Middle brook broth and Bactec AFB media
  16. 16. Laboratory Diagnosis of Extra-Pulmonary TB Same as mentioned for pulmonary TB, but by collecting the appropriate specimens. However, specimens collected from normally sterile sites, e.g. CSF, do not require decontamination.
  17. 17. Tuberculin Skin Test (TST) Principle: detects a delayed type hypersensitivity (DTH) response to previous exposure of the host to tubercle bacilli.
  18. 18. Interpretation of the Tuberculin Skin Test An induration of 10 millimeters or more is considered positive
  19. 19. Prevention is Always Better than Treatment 1. General Measures e.g., Pasteurization of milk. 2. Treatment of latent tuberculosis. 3. BCG Vaccine.
  20. 20. MCQ Questions 1.M. tuberculosis are characterized by being: a.Strict anaerobes b.Acid fast bacilli c.Capsulated d.Motile e.Able to grow on ordinary media
  21. 21. 2.One of the following media is used for growing M. tuberculosis: a.MacConkey’s agar b.Blood agar c.Nutrient agar d.Lowenstein Jensen medium e.Loeffler’s serum
  22. 22. 3.The following methods are used in the diagnosis of pulmonary tuberculosis except: a.Examination of ZN stained direct sputum smear b.PCR of sputum c.Culture on selective medium d.BACTEC AFB system e.Detection of specific antibodies
  23. 23. Thank You