Mycobacteria TB, is a causative agent of Tuberculosis.
Characteristics:
Morphology:
- Organism is rod shaped, thin and commonly straight, but may be found in bent or club shaped appearance.
- They appear in the form of microscopic "serpentine cords"
- They are not encapsulated..
- They are non motile
- They don't form spores.
Staining:
They are not stained by ordinary Gram staining technique. The are stained by Ziehl-Nelson Staining. it is also called acid fast staining.
one of the characteristic of mycobacterium is that it retain dye even after washing with alcohol.
Growth Characteristics.
These are obligate aerobes that is why the infect highly oxygenated tissues like lungs, kidney brain etc.
They use carbon compounds as a source of energy.
the optimum temperature is 37 degree centigrade.
Growth is inhibited by heat or pasteurization.
Growth is increased by 5 - 10 percent carbondioxide.
Doubling time is 18 hours.
They are resistant to drying, many chemicals, dyes and many antimicrobial agents.
Antigens:
Glycolipids, that is mycolic acid bound to carbohydrates.
these include, cord factor, sulfatides and wax D
Phospholipids, these induce caseation necrosis.
Polysacharides (cause hypersensitivity.)
Protein antigens; non virulent, induce host immunity, induce tuberculin reaction and antibody formation.
Habitat.
They are found in highly oxygenated tissues of human body. forexample, lungs, kidney, brain and bones.
Transmission.
Transmission is person to person through droplets produced by coughing.
Pathogenesis:
Mycobacterium TB is inhaled to the lungs where it reaches to alveoli. In the alveoli it proliferate and produce following type of lessions.
Exudative Lession;
It is acute inflamatory response to infiltrating bacteria. It consist of neutrophill infilration, edema formation in the alveoli. it may heal by resolution with absorption of exudate or lead to necrosis of lung tissue or may proceed to the granulomatous lesion.
Granulomatous lesion:
This is an inflammatory pattern consisting of three zones.
1. central zone of necrosis and giant cells containing mycobacteria.
2. Middle zone of epitheliod cells.
3. Peripheral zone of fibroblasts, lymphocytes and monocytes.
Spread of Mycobacterium TB to other Organs.
1. A tubercle may erode in to bronchus and enter the blood stream and spread to other organs.
2. It may be swallowed and enter into GIT and can cause TB of GIT.
3. To other parts of lungs.
4. To other persons through droplets.
Clinical Findings / Signs and symptoms of TB.
Granulomatous lesion:
This is an inflammatory pattern consisting of three zones.
1. central zone of necrosis and giant cells containing mycobacteria.
2. Middle zone of epitheliod cells.
3. Peripheral zone of fibroblasts, lymphocytes and monocytes.
Spread of Mycobacterium TB to other Organs.
1. A tubercle may erode in to bronchus and enter the blood stream and spread to other organs.
2. It may be swallowed and enter into GIT and can cause TB of GIT.
3. To other parts of lungs.
4. To other persons through droplets.
Clinical Findings / Signs and symptoms of TB.
- Fever, intermittent, low grade, appear at late afternoon than subsides,
- night sweats
- malaise
- weakness
- Anorexia (loss of appetite)
- Cough , first with white sputum than yellow and still later becomes bloody.
- Pain in chest
- Scrofula that is presence of non tender unilateral cervical lymph nodes.
- Erythma nodosum, charachterized by presence of tender nodules along the extensor surfaces of tibia and ulna.
- Pott's disease that is tuberculous osteomytitis of the vertebral bodies.
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