DPT - Microbiology II (Acid fast Bacilli) - Mycobacteria

DPT - Microbiology II (6th semester)

1. PATHOLOGY & MICROBIOLOGY - II by, Miss Areesha Ahmad Lecturer Microbiology B.Sc (H), M.Sc , M.Phil and Ph.D scholar (Microbiology) Medical Microbiology Acid fast Bacilli Mycobacteria

2. The high lipid content (approximately 60%) of their cell wall makes mycobacteria acid-fast.

3. Acid-fast bacilli (AFB) Acid-fast bacilli (AFB) refer to bacteria that are resistant to decolorization by acids during staining procedures, particularly the Ziehl-Neelsen or Kinyoun acid-fast stain. This property is mainly due to the high lipid content (particularly mycolic acid) in their cell walls. The term "acid-fast" means these bacteria can retain the primary stain ( carbolfuchsin ) even after being treated with an acid-alcohol solution, which removes the stain from non-acid-fast cells.

4. Important Properties: This organism causes tuberculosis. Worldwide, M. tuberculosis causes more deaths than any other single microbial agent. Mycobacterium tuberculosis grows slowly . Because growth is so slow, cultures of clinical specimens must be held for 6 to 8 weeks before being recorded as negative . Mycobacterium tuberculosis is relatively resistant to acids and alkalis. M. tuberculosis is resistant to dehydration and therefore survives in dried expectorated sputum; this property may be important in its transmission by aerosol. The organism also contains several proteins, which, when combined with waxes, elicit delayed hypersensitivity. These proteins are the antigens in the purified protein derivative (PPD) skin test (also known as the tuberculin skin test).

5. Transmission Mycobacterium tuberculosis is transmitted from person to person by respiratory aerosols produced by coughing. The portal of entry is the respiratory tract and the initial site of infection is the lung . In tissue, it resides chiefly within reticuloendothelial cells (e.g., macrophages ). Macrophages kill most, but not all, of the infecting organisms. The ones that survive can continue to infect other adjacent cells or can disseminate to other organs . Humans are the natural reservoir of M. tuberculosis.

6. Pathogenesis Mycobacterium tuberculosis produces no exotoxins and does not contain endotoxin in its cell wall . The organism preferentially infects macrophages and other reticuloendothelial cells. Mycobacterium tuberculosis survives and multiplies within a cellular vacuole called a phagosome . The organism produces a protein called “ exported repetitive protein ” that prevents the phagosome from fusing with the lysosome, thereby allowing the organism to escape the degradative enzymes in the lysosome.

7. Lesions are dependent on the presence of the organism and the host response. There are two types of lesions: ( 1) Exudative lesions , which consist of an acute inflammatory response and occur chiefly in the lungs at the initial site of infection . ( 2) Granulomatous lesions , which consist of a central area of giant cells ( fusion of various cells such as macrophage, epithelioid cells, monocytes, etc ) containing tubercle bacilli surrounded by a zone of epithelioid cells. These giant cells, called Langhans ’ giant cells, are an important pathologic finding in tuberculous lesions. A tubercle is a granuloma surrounded by fibrous tissue that has undergone central caseation necrosis . Tubercles heal by fibrosis and calcification.

8. The primary lesion of tuberculosis usually occurs in the lungs . The exudative lesion and the draining lymph nodes together are called a Ghon complex. Reactivation lesions also occur in other well-oxygenated sites such as the kidneys, brain, and bone. Reactivation is seen primarily in immunocompromised or debilitated patients.

9. Clinical findings Clinical findings are protean; many organs can be involved . Fever, fatigue, night sweats, and weight loss are common. The main findings in pulmonary tuberculosis are cough and hemoptysis. Scrofula is mycobacterial cervical lymphadenitis that presents as swollen lymph nodes . Erythema nodosum , characterized by tender nodules (small, raised lumps or bumps on the skin) along the extensor surfaces of the tibia (Shin Bone) and ulna (Forearm Bone), is a manifestation of primary infection seen in patients who are controlling the infection with a potent cell-mediated response.

10. Miliary tuberculosis is a form of tuberculosis that occurs when the Mycobacterium tuberculosis bacteria spread from the lungs to other parts of the body through the bloodstream . This type of TB is characterized by a widespread distribution of small, nodular lesions (about 1-5 mm in size) resembling millet seeds (small, round), hence the name " miliary ." Tuberculous meningitis and tuberculous osteomyelitis , especially vertebral osteomyelitis (Pott’s disease), are important disseminated forms. Gastrointestinal tuberculosis is characterized by abdominal pain and diarrhea accompanied by more generalized symptoms of fever and weight loss .

11. R enal tuberculosis , dysuria (painful or difficult urination) and hematuria (blood in the urine). Sterile pyuria (presence of white blood cells (WBCs) in urine. M ost (approximately 90%) infections with M. tuberculosis are asymptomatic. Asymptomatic infections, also known as latent infections, can reactivate and cause symptomatic tuberculosis.

12. Laboratory diagnosis Specimen : Fresh sputum P leural fluid (fluid found in the pleural space eg ., the membranes lining the lungs and the chest cavity). C erebrospinal fluid U rine Biopsy material 1) Microscopy: S mears stained by the Ziehl-Neelsen method. M . tuberculosis in urine M . tuberculosis in sputum

13. Laboratory diagnosis S putum 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 .

14. Laboratory diagnosis 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 . 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.

15. Laboratory diagnosis

16. 4.Direct detection by using nucleic acid amplification (NAA) test : T his test can reliably detect M. tuberculosis bacteria in specimens in hours as compared to weeks for culture. Chest X-Ray Laboratory diagnosis

17. Prevention To reduce infection risk, E nsure good ventilation . U se natural light. Wear Mask P ractice good hygiene by covering mouth and nose when coughing or sneezing .

18. LN infections: Lymphadenitis is an infection in one or more lymph nodes

19. Ozonization is a chemical process that uses ozone (gas) to treat water and remove pollutants Pseudo - outbreaks  are defined as an increase in identified organisms but without evidence of infection.

20. Lab diagnosis Mycobacterium avium complex

21. Mycobacterium avium complex

22. (lymph nodes in the neck to become enlarged)

23. Bacillus Calmette -Guerin (BCG) vaccine is a live attenuated vaccine that's used to prevent tuberculosis (TB) and other mycobacterial infections

24. Isoniazid (INH) is an antibiotic indicated in the first-line treatment of active Mycobacterium tuberculosis (TB) infection.

25. (Cell-mediated immunity)

26. I ntraperitoneal (thin membrane that lines the abdominal cavity and contains the abdominal organs)

27. Case Mix Index (CMI) The leprosy test involves injection of an antigen just under the skin to determine if your body has a current or recent leprosy infection.

28. Case Mix Index (CMI)

29. Tuberculoid Leprosy Lepromatous Leprosy

30. Delayed-type hypersensitivity (DTH) is a type of immune response that occurs when the body's T cells are activated by an antigen-presenting cell

31. A lepromin test is a skin test that helps determine the type of leprosy a person has by measuring their body's reaction to an inactivated extract of the leprosy bacillus: An extract of the leprosy bacillus is injected under the skin, and the injection site is examined after 3 and 28 days Skin changes at the injection site indicate the presence of leprosy

32. ( Tuberculoid Leprosy) ( Lepromatous Leprosy) Anti-phenolic glycolipid-1 (PGL-1) antibodies are  a marker for Mycobacterium leprae (M. leprae ) infection and can help diagnose leprosy

33. Dapsone is an antibiotic medication used in multidrug regimens  Multidrug therapy (MDT) Case mix indexes  The only available vaccine for leprosy is the Bacille Calmette-Guérin (BCG) vaccine, which is also used to protect against tuberculosis (TB).