Mycobacteria Flashcards
Non-motile, non-spore forming and aerobic bacilli. They are slightly curved, sometimes filamentous and branching. Weakly gram-positive but stain poorly with gram stain.
Cell wall is thick which makes it resistant to commonly used disinfectants and laboratory staining reagents and difficult to stain. Once stained, they resist decolourization with acid and alcohol solution. Therefore, they are also called acid-fast bacilli (AFB).
Ziehl-Neelsen staining is used to demonstrate acid fastness of the bacteria and stain bright red.
Mycobacterium
What are the two human pathogens under Mycobacterium?
Mycobacterium tuberculosis
Mycobacterium leprae
How is Mycobacterium different from Gram-positive and negative bacteria?
They have mycolic acids and arabino galactan.
Which component of the lipids of the Mycobacterium cell wall is responsible for:
a) acid fastness
b) slow growth by delaying permeation of nutrients
c) resistance to commonly used antibiotics
d) resistance to detergents
e) unusual resistance to killing by acids and alkaline
Mycolic acid
- cause tuberculosis
- slow growing than average bacteria
- obligate aerobes
- long chain fatty acids called mycolic acids in the cell wall
- strong acid fast bacteria
Mycobacterium tuberculosis
- most widely used medium is Lowenstein-Jensen (LJ) medium
- produces yellowish or buff-coloured colonies
Mycobacterium tuberculosis
Which mycobacterium causes these populations at the greatest risk:
- immunocompromised patients (especially those with HIV)
- drug and alcohol abusers
- homeless people
- individuals exposed to infected patients
Mycobacterium tuberculosis
The followings are the virulence factors for Mycobacterium…
- intracellular growth in alveolar macrophages
- does not produce any toxin
- cord factors and sulfolipids are toxic substances produced by the mycobacterium
Tuberculosis
The followings are the virulence factors for Mycobacterium…
- intracellular growth in alveolar macrophages
- does not produce any toxin
- cord factors and sulfolipids are toxic substances produced by the mycobacterium
Tuberculosis
- Human beings are the only source and natural reservoir for Mycobacterium…..
- Transmitted by inhalation of infectious aerosolized droplets
Tuberculosis
Explain the pathogenic life cycle of M. tuberculosis
- M. tuberculosis enters the respiratory airways
- Infectious particles penetrate the alveoli and phagocytized by alveolar macrophages
- Bacteria able to invade the immune system and replicate
- Granuloma is formed, where alveolar macrophages, epithelioid cells, and Langhans giant cells with intracellular mycobacteria form the central core of a necrotic mass that is surrounded by a dense wall of macrophages and CD4, CD8, and NK T cells.
- The cavities may rupture into blood vessels, causing dissemination of mycobacteria in the body or these may rupture into airways, releasing mycobacterium in aerosol or sputum.
Productive cough, fever, weight loss, hemoptysis or chest pain, night sweats, fatigue, anorexia, and the sputum may be scanty or bloody and purulent. necrosis in lung tissue.
Pulmonary tuberculosis
A result of spread of the bacilli through blood circulation during the initial stage of multiplication.
Extrapulmonary tuberculosis
- Genitourinary tuberculosis
- Miliary tuberculosis
- Gastrointestinal tuberculosis
- Skeletal tuberculosis
- Tubercular lymphadenitis
- Other conditions
- Erythema nodosum
Infections of extrapulmonary tuberculosis
Mantoux test / Tuberculin skin test
A screening test done on the skin for diagnosis of TB using Purified Protein Derivative (PPD)
A positive skin test indicates hypersensitivity of the individual to protein (small bleb) which suggests infection with M. tuberculosis or immunization by BCG vaccination
