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Mycobacteria - Prac. Microbiology
This document discusses the characteristics and diagnosis of Mycobacterium tuberculosis, the bacteria that causes tuberculosis. Key points include: - Mycobacterium species are acid-fast bacilli that grow slowly, including M. tuberculosis, M. bovis, and M. leprae. - M. tuberculosis is transmitted via inhalation of droplets from infected individuals and causes pulmonary tuberculosis as well as extra-pulmonary disease. - Diagnosis involves smear microscopy, culture, and molecular tests of sputum samples, as well as tuberculin skin testing. Lowenstein-Jensen medium and BACTEC systems can be used for culture.
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Mycobacteria - Prac. Microbiology
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- 2. Characters • Acid-alcohol fastness •Slow rate of growth
- 3. Members of theGenus 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. 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.
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- 6. Ziehl-Neelsen (Z-N) Stain •Carbol-fuchsin dye • Heat • Acid-alcohol (decolourization) • Methylene blue • Acid-fast = Mycobacteria
- 7. Cultural Characters Media include: -Lowenstein-Jensen (L-J) medium - Middlebrook's medium
- 8. Cultural Characters • Strictaerobe (5 - 10% CO2 stimulates its growth). • Colonies appear after 2-4 weeks of incubation at 37°C and may be delayed to 8 weeks.
- 10. Human Tuberculosis Mode ofInfection 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).
- 11. Oral mainfestations oftuberculosis 1. Primary complex 2. Oral ulceration secondary to pulmonary tuberculosis 3. Lupus vulgaris 4. Tuberculous periapical infection and osteomyelitis.
- 12. Laboratory Diagnosis ofOpen Pulmonary TB Specimens: include sputum, BAL Early morning sputum specimens collected on 3 consecutive days, from a deep productive cough, give the best results
- 13. Direct Detection: 1. Smears: Ziehl-Neelsen(Z-N). Under the ordinary light microscope, AFB appear pink in a blue background.
- 14. 2. Molecular tests: •For rapid detection • Expensive
- 15. Cultivation: Conventional culture media: (incubatedin 5 – 10% CO2 at 37o C): L-J tube - Results may be relatively delayed (2-8 weeks).
- 16. Fluid Medium Systems (4-14days identification) Middle brook broth and Bactec AFB media
- 18. Laboratory Diagnosis of Extra-PulmonaryTB 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.
- 19. Tuberculin Skin Test (TST) Principle: detectsa delayed type hypersensitivity (DTH) response to previous exposure of the host to tubercle bacilli.
- 20. Interpretation of theTuberculin Skin Test An induration of 10 millimeters or more is considered positive
- 21. Prevention is AlwaysBetter than Treatment 1. General Measures e.g., Pasteurization of milk. 2. Treatment of latent tuberculosis. 3. BCG Vaccine.
- 22. MCQ Questions 1.M. tuberculosisare characterized by being: a.Strict anaerobes b.Acid fast bacilli c.Capsulated d.Motile e.Able to grow on ordinary media
- 23. 2.One of thefollowing 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
- 24. 3.The following methodsare 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
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