Notes on Mycobacterium

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Genus: Mycobacterium.

• Obligate, aerobic, acid-fast rod with waxy cell wall.

• Thick, waxy cell wall resistant to desiccation, chemicals, and UV.

• Has a waxy cell wall that resists staining; acid-fast.

• Includes the harmless saprophytes that live on dead/decaying matter.

• Gram-positive pleomorphic rods.

• Two notable species include Mycobacterium tuberculosis and Mycobacterium leprae.

Mycobacterium tuberculosis.

• Auramine-rhodamine staining bacilli.

• Acid-fast.

• Grows on Lowenstein-Jensen medium.

• Produces niacin.

• Produces heat-sensitive catalase.

Initial TB infection:

Peripheral pulmonary focus of infection accompanied by mediastinal or hilar lymphadenopathy evident on chest x ray. Asymptomatic infection.

Reactivation TB tuberculosis:

Fever, night sweats, fatigue, weight loss, productive cough, hemoptysis and pleuritic chest pain. Chest x ray reveals an apical cavitary pulmonary lesion. Reaction tuberculosis occurs in the apices because the oxygen concentration is the highest there. Common in HIV patients.

Habitat:

• Human lungs.

Transmission:

• Transmitted by respiratory droplets.

Pathogenesis:

• Sulfatides: inhibit phagosome-lysosome fusion.

• Cord factor: inhibits leukocyte migration, disrupts mitochondrial respiration and oxidative phosphorylation.

• Tuberculin: delayed hypersensitivity, and invoke cell-mediated immunity.

Disease:

• TB: also caused by Mycobacterium bovis.

• Pulmonary, urinary, or any organ, or miliary.

• Organisms replicate in macrophages.

• Most people heal without disease; organisms walled off in the Ghon complex.

Diagnosis:

• Auramine-rhodamine stain; organism seen in microscope; PPD skin test; organism produces niacin and are catalase -.

• Treatment: isoniazid, rifampin, and pyrazinamide (first two months).

• Isoniazid and rifampin (next two months).

Vaccine:

• BCG vaccine.

Mycobacterium leprae.

• Acid-fast, obligate intracellular rods.

• Found on human mucosa, skin and nerves; armadillos in Texas and Louisiana.

• Transmission is by nasal discharge.

Two forms of Leprosy:

• Tuberculoid: Lepromin test+; less damaging; macular; nerve enlargement; paresthesia.

• Lepromatous: Lepromin test-; more damaging; Leonine facies, paresthesia.

Test:

• Lepromin skin test; punch biopsy or nasal scrapings; acid fast stain.

Treatment:

• Dapsone and rifampin; clofazimine added for lepromatous.

Additional Readings:

Basic Bacteriology

1. Bacterial Locations and Toxins
2. Growth Medias and Oxygen Requirements
3. Staphylococus
4. Streptococcus
5. Enterococcus
6. Bacillus
7. Listeria
8. Corynebacterium
9. Actinomyces
10. Nocadria
11. Mycobacterium
12. Clostridium
13. Neisseria
14. Pseudomonas
15. Legionella
16. Bordetella
17. Francisella
18. Brucella
19. Campylobacter
20. Escherichia
21. Shigella
22. Klebsiella
23. Salmonella
24. Yersinia
25. Proteus
26. Vibrio
27. Pasteurella
28. Haemophilus
29. Bacteriodes and Prevotella
30. Treponema
31. Borrelia
32. Rickettsia
33. Coxiella
34. Ehrlichia
35. Chlamydia
36. Mycoplasma
37. What is an ELEK's Test?
38. Causes of Orchitis
39. What is Leprosy?
40. What is Folliculitis?
41. What is Botulism?
42. How to interpret PPD (Purified Protein Derivative) results?
43. Prenatal Infections

Related Topics

1. Bacterial vs viral infections

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