Etiology
This bacterium is the causative agent of tuberculosis.
What is Mycobacterium tuberculosis
This waxy molecule in the cell wall makes M. tuberculosis resistant to desiccation and disinfectants.
What is mycolic acid?
The thick lipid-rich cell wall containing mycolic acids contributes to the organism’s environmental persistence and acid-fastness.
These immune cells are the primary site of bacterial replication during early infection.
What are alveolar macrophages?
M. tuberculosis infects and multiplies within alveolar macrophages after inhalation into the terminal airways.
In this stage of tuberculosis, the infection is contained by the immune system, there are no symptoms, and the person is not contagious, though viable bacteria remain dormant in granulomas.
What is latent tuberculosis infection?
Latent TB occurs after the immune system successfully walls off Mycobacterium tuberculosis within granulomas. The bacteria remain viable but inactive. Individuals are asymptomatic and non-infectious, but reactivation can occur if immunity declines.
This special staining method is used to visualize M. tuberculosis under the microscope.
What is the Ziehl–Neelsen acid-fast stain?
The Ziehl–Neelsen stain detects acid-fast organisms whose waxy cell walls resist decolorization by acid alcohol. Acid-fast bacilli appear red against a blue background.
This lipid, also called trehalose dimycolate, is responsible for the “serpentine” appearance of the bacteria in culture.
What is cord factor?
Cord factor promotes virulence by inhibiting neutrophil migration and stimulating TNF-α release, aiding granuloma formation.
This T-helper subset plays a central role in activating macrophages to kill intracellular mycobacteria.
What are Th1 cells?
Th1 cells release a cytokine that enhances macrophage bactericidal activity and supports granuloma maintenance.
This initial pulmonary lesion forms in the mid- or lower lobes during primary TB infection.
What is the Ghon focus?
The Ghon focus is the first area of inflammation and granuloma formation after primary infection in the lungs.
This component of the bacterial cell wall is responsible for the acid-fast property of M. tuberculosis.
What is mycolic acid?
Mycolic acids are long-chain fatty acids in the cell wall that confer resistance to acids, detergents, and many antibiotics.
This glycolipid inhibits phagosome–lysosome fusion inside macrophages.
What are sulfatides?
Sulfatides block phagolysosomal fusion, allowing intracellular survival of M. tuberculosis within macrophages.
This cytokine, secreted by Th1 cells, enhances macrophage microbicidal activity.
What is interferon-gamma (IFN-γ)?
IFN-γ promotes phagosome maturation and production of reactive nitrogen intermediates for bacterial killing.
The combination of the Ghon focus, lymphatic vessels, and regional lymph nodes is called this.
What is the Ghon complex?
The Ghon complex reflects the spread of infection to regional lymphatics and lymph nodes.
This test, based on a delayed-type hypersensitivity reaction, can indicate prior exposure to M. tuberculosis.
What is the tuberculin skin test (Mantoux test)?
The test measures immune response to purified protein derivative (PPD) and reflects prior sensitization to mycobacterial antigens.
This cytokine promotes granuloma formation and limits infection spread, but excessive amounts cause tissue damage.
What is tumor necrosis factor-alpha (TNF-α)?
TNF-α recruits immune cells and maintains granuloma structure, but overproduction contributes to caseous necrosis and lung injury.
Reactivation TB typically occurs in these parts of the lungs, which have higher oxygen tension.
What are the upper lobes?
M. tuberculosis is an obligate aerobe, so reactivation favors oxygen-rich upper lung zones.
These two bacterial species are part of the Mycobacterium tuberculosis complex and can also cause human TB.
What are Mycobacterium bovis and Mycobacterium africanum ?
Both belong to the M. tuberculosis complex. M. bovis can infect humans via unpasteurized milk, while M. africanum is mainly seen in West Africa.
This type of hypersensitivity reaction, mediated by T cells and macrophages, is responsible for granuloma formation in TB.
What is a type IV (delayed-type) hypersensitivity reaction?
The Th1-mediated immune response leads to macrophage activation and granuloma formation, characteristic of TB pathology.
This disseminated form of TB is characterized by tiny granulomas throughout many organs.
What is miliary tuberculosis?
Miliary TB results from hematogenous spread of M. tuberculosis, producing numerous small nodules in multiple organs.