1. Mycobacteria Dr Sadia Ikram

2. Mycobacteria Aerobic, acid-fast bacilli (rods). Neither Gram-positive nor Gram-negative. Stained poorly by Gram stain. Obligate aerobe: Cause disease in highly oxygenated tissues (Upper lobe of lung & kidney). Only acid-fast bacteria.

4. Acid-fast: Organism's ability to retain carbol fuchsin stain despite subsequent treatment with an ethanol–hydrochloric acid mixture. (decolorizer). High lipid content (approximately 60%) in cell wall makes them acid-fast.

5. speciesRate of growth on media Mode of transmissionSite of Infection M. tuberculosisSlow (weeks)Respiratory dropletsLungs M. bovisSlow (weeks)Milk from infected animalsIntestinal M. lepraeNoneProlonged close contactSkin, nerves M. kansasiiSlow (weeks)Soil and water- M. marinumSlow (weeks)water- M. avium-intracellulare complex Slow (weeks)Soil and waterLungs M. fortuitum-chelonei complex Rapid (days)Soil and water- Medically Relevant species of Mycobacteria

6. Mycobacterium tuberculosis Causes tuberculosis. Causes more deaths than any other microbial agent. One-third of the world's population infected with this organism. High mortality. Grows slowly (i.e., doubling time of 18 hours). Culturing time: 6 to 8 weeks.

7. Media for culture: Löwenstein-Jensen medium. Contain complex nutrients (e.g., egg yolk) Dyes (e.g., malachite green), which inhibit unwanted normal flora present in sputum samples.

8. Cell wall contains several complex lipids Long-chain (C 78 –C 90 ) fatty acids (mycolic acids), contribute to organism's acid-fastness. Wax D: Enhance immune response to many antigens. Phosphatides: Role in caseation necrosis.

9. Transmission Transmitted from person to person by respiratory aerosol. Initial site of infection: Lung. Resides chiefly within reticulo-endothelial cells. e.g., macrophages. Humans : Natural reservoir of M. tuberculosis. Some animals can be infected.

10. Pathogenesis Produces no exotoxins. Does not contain endotoxin in cell wall. Infects macrophages and other RE cells. Multiplies within a cellular vacuole called a phagosome Prevents phagosome from fusing with lysosome, thereby allowing the organism to escape the degradative enzymes in lysosome.

12. IL-2

13. Lesions Exudative lesions: consist of acute inflammatory response. Occur chiefly in lungs at initial site of infection. Granulomatous lesions: consist of a central area of giant cells containing tubercle bacilli surrounded by a zone of epithelioid cells. Giant cells, called Langhans' giant cells. A tubercle is a granuloma surrounded by fibrous tissue that has undergone central caseation necrosis. Tubercles heal by fibrosis and calcification.

15. Primary and Secondary Lesions Primary lesion of tuberculosis occurs in lungs. Parenchymal exudative lesion and draining lymph nodes together are called a Ghon complex. Primary lesions usually occur in lower lobes. Reactivation lesions usually occur in apices and other well-oxygenated sites like kidneys, brain, and bone. Seen primarily in immuno- compromised or debilitated patients.

17. Spread of the organisms occurs by two mechanisms: A tubercle can erode into a bronchus, empty its caseous contents, and spread organism to other parts of lungs, gastrointestinal tract if swallowed, and to other persons if expectorated. Can disseminate via bloodstream to many internal organs. Dissemination can occur at an early stage if cell-mediated immunity fails to contain the initial infection or at a late stage if a person becomes immuno-compromised.

18. Clinical Features Fever, fatigue, night sweats, and weight loss. Pulmonary tuberculosis causes cough and hemoptysis. Gastrointestinal tuberculosis: characterized by abdominal pain and diarrhea, intestinal obstruction or hemorrhage. Renal tuberculosis, dysuria, hematuria & flank pain. "Sterile pyuria" a characteristic finding.

19. Laboratory diagnosis 1. Acid-fast staining of sputum. 2. Culture: Digestion of the specimen by treatment with NaOH and concentration by centrifugation, and cultured on Löwenstein- Jensen agar for up to 8 weeks. 3. Organism identified by biochemical tests. M. tuberculosis produces niacin, whereas almost no other Mycobacteria do. 4. Catalase positive.

21. AFB Acid Fast Bacilli

22. Culture on L J medium

23. 5. PPD skin test. 6. Interferon-gamma release assay (IGRA) called Quantiferon-TB: blood cells from the patient are exposed to antigens from M. tuberculosis and the amount of interferon-gamma released from the cells is measured. 7. Histopathology.

24. Treatment Multidrug therapy: Used to prevent emergence of drug-resistant strains. 6- to 9-month duration of treatment. Isoniazid (INH). Rifampin. Pyrazinamide. Ethambutol.

26. Prevention BCG vaccine can be used to induce partial resistance to tuberculosis. The vaccine contains a strain of live, attenuated M. bovis called Bacillus Calmette-Guérin. Effective in preventing appearance of tuberculosis as a clinical disease, especially in children, Does not prevent infection by M. tuberculosis. Pasteurization of milk and destruction of infected cattle important in preventing intestinal tuberculosis.