Tuberculosis Flashcards
TB is caused by bacteria of the ____
Mycobacterium tuberculosis complex.
TB most often affects the ____
lungs
Mode of transmission of TB
Airborne spread of droplet nuclei
The most common and important agent of human disease by far is ___
M. tuberculosis (sensu stricto)
It is resistant to pyrazinamide and historically caused TB from unpasteurized milk.
M bovis
Morphology and structure of M Tuberculosis
Rod-shaped, non-spore-forming, thin aerobic bacterium
Size: 0.5 μm by 3 μm.
Acid fastness attributed to high ____ and lipid content in the cell wall.
mycolic acid
Low permeability due to ____ and ____reducing antibiotic effectiveness
arabinogalactan and peptidoglycan
ALso contains _____, which aids in survival within macrophages.
lipoarabinomannan
High ____ content (65.6%), indicative of an aerobic “lifestyle.”
guanine-plus-cytosine
Most commonly transmitted from a person with infectious pulmonary TB by ________ containing M Tuberculosis bacteria
droplet nuclei
Droplets dry rapidly and the smallest (____) remain airborne for hours and may reach terminal air passages
<5–10 μm
A single cough may release up to ____ infectious droplet nuclei.
3000
Who are the most likely to transmit the infection>
Sputum smear–positive cases with visible AFB
The most infectious patients have cavitary pulmonary TB or much less commonly laryngeal TB and produce sputum containing ____
105–107 AFB/mL
Smear-negative/culture-positive TB patients are less infectious but responsible for ~___% of transmissions in some studies.
20
T/F
Culture-negative pulmonary TB and extrapulmonary TB are essentially noninfectious.
T
Persons with BOTH HIV Infection and TB are less likely to have cavitations and may be less infectious than persons without HIV Infection T/F
T
One of the most important factors in transmission of tubercle bacilli because it increases the intensity of contact with a case
Poorly ventilated, crowded settings
In high-prevalence settings, up to___ contacts may be infected per AFB-positive case before diagnosis.
20
Most potent risk factor for TB among infected individuals, directly related to degree of immunosuppression
HIV co-infection
Incidence of TB is highest during ___
late adolescence
early adulthood
Clinical illness following initial infection is classified as
Primary TB
In the early phases of infection, the predominant cells infected by M Tuberculosis
Myeloid dendritic cells
Plays a role in determining susceptibility to TB
NRAMP 1
Used primarily for the diagnosis of M tuberculosis infection in persons without symptoms.
TST
T/F
TST positive persons are less susceptible to a new M Tuberculosis infection than TST negative persons
T
Which cell type is primarily responsible for the initial phagocytosis of Mycobacterium tuberculosis in the alveoli?
A. CD4+ T lymphocytes
B. Dendritic cells
C. Alveolar macrophages
D. Neutrophils
C
Alveolar macrophages are the first immune cells to phagocytose M. tuberculosis in the alveoli, although they are initially unactivated and susceptible to bacillary growth.
Which protein antigen of Mycobacterium tuberculosis is critical for granuloma formation by inducing the secretion of matrix metalloproteinase 9 (MMP9)?
A. Lipoarabinomannan
B. ESAT-6
C. 19-kDa lipoprotein
D. CFP-10
B
ESAT-6 induces epithelial cells in contact with infected macrophages to secrete MMP9, which recruits naïve macrophages and promotes granuloma maturation.
What is the main cytokine produced by TH1 cells that activates macrophages in TB immunity?
A. IL-10
B. TNF-α
C. IL-4
D. IFN-γ
D
TH1 cells produce IFN-γ, which is crucial for activating macrophages to kill M. tuberculosis and initiate bactericidal responses.
Which component of M. tuberculosis inhibits phagosome-lysosome fusion within macrophages?
A. Phosphatidylinositol 3-phosphate
B. Lipoproteins
C. Lipoarabinomannan
D. Cyclic AMP
C
Lipoarabinomannan interferes with the Ca²⁺/calmodulin pathway, blocking phagosome-lysosome fusion and enabling bacillary survival within macrophages.
Which gene product of M. tuberculosis is responsible for its persistence during chronic infection in mice by facilitating growth on fatty acid substrates?
A. katG
B. RD1
C. icl1
D. carD
C
What is the function of the NRAMP1 gene in resistance to Mycobacterium tuberculosis?
A. Phagosome-lysosome fusion
B. Regulation of reactive oxygen intermediates
C. Resistance to oxidative stress
D. Regulation of macrophage susceptibility
D
Which term is increasingly used to describe bacilli that remain active but undetectable during the so-called “latent” stage?
A. Biofilm bacilli
B. Dormant bacilli
C. Persisters
D. Latent bacilli
C
In HIV-infected individuals, which T-cell defect is most responsible for uncontrolled M. tuberculosis proliferation?
A. CD8+ T-cell lysis
B. CD4+ T-cell quantitative and qualitative defect
C. Regulatory T-cell dysfunction
D. Natural killer cell depletion
B
Which cytokines are primarily produced by TH2 cells?
A. IFN-γ and IL-2
B. IL-4, IL-5, IL-10, and IL-13
C. TNF-α and IL-1
D. IL-17 and IL-22
B
What is the role of the 19-kDa lipoprotein of M. tuberculosis?
A. Inhibits macrophage apoptosis
B. Triggers Toll-like receptor signaling in dendritic cells
C. Promotes granuloma formation
D. Blocks phagosome-lysosome fusion
B
How do granulomas inhibit bacillary growth in their necrotic centers?
A. By recruitment of CD8+ T cells
B. By maintaining low oxygen tension and pH
C. By inducing TNF-α secretion
D. By phagolysosome fusion
B
Which cytokine is most critical for macrophage activation during the macrophage-activating response?
A. IL-1
B. IFN-γ
C. TNF-α
D. IL-10
B
Which type of T cell has been associated with cytotoxic responses and lysis of M. tuberculosis-infected cells?
A. TH1 cells
B. TH2 cells
C. CD8+ T cells
D. γδ T cells
C
- What mechanism allows M. tuberculosis to prevent autophagy within infected macrophages?
A. Inhibition of phagosome acidification
B. Blockade of Ca²⁺/calmodulin pathway
C. Reduction in phosphatidylinositol 3-phosphate production
D. All of the above
D
Which member of the Mycobacterium tuberculosis complex is most commonly associated with zoonotic transmission through unpasteurized milk?
A. Mycobacterium africanum
B. Mycobacterium bovis
C. Mycobacterium caprae
D. Mycobacterium orygis
B
What characteristic of M. tuberculosis justifies its classification as an acid-fast bacillus (AFB)?
A. Its high lipid content in the cell wall, including mycolic acids
B. Its rod shape and non-spore-forming nature
C. Its aerobic metabolism
D. Its ability to grow on fatty acid substrates
A
The high content of mycolic acids and other lipids in the M. tuberculosis cell wall makes it resistant to decolorization by acid alcohol, a defining feature of acid-fast bacilli (AFB).
What genomic feature of M. tuberculosis contributes to its persistence and adaptability in the host?
A. High guanine-plus-cytosine content
B. Absence of an environmental reservoir
C. Limited genetic variability among global strains
D. Lack of a complete vesicular proton-ATPase
A
The M. tuberculosis genome has a high guanine-plus-cytosine content (65.6%), reflecting its aerobic lifestyle and ability to adapt to hostile environments, which aids its persistence in the host.
Which of the following organisms is part of the Mycobacterium tuberculosis complex and infects marine animals such as seals and sea lions?
A. Mycobacterium africanum
B. Mycobacterium pinnipedii
C. Mycobacterium mungi
D. Mycobacterium microti
B
What is the role of the katG gene in M. tuberculosis?
A. It encodes the catalase/peroxidase enzyme that activates isoniazid.
B. It is required for the glyoxylate shunt in chronic infections.
C. It facilitates the secretion of ESAT-6 and CFP-10 antigens.
D. It enhances the resistance of M. tuberculosis to acid-fast staining.
A
What is the primary route of transmission of Mycobacterium tuberculosis?
A. Skin contact with infected individuals
B. Inhalation of droplet nuclei containing bacilli
C. Ingestion of contaminated food
D. Direct blood contact with infected individuals
B
The primary mode of M. tuberculosis transmission is via inhalation of droplet nuclei (<5–10 μm) that remain suspended in the air for hours after being expelled by coughing, sneezing, or speaking by individuals with infectious TB.
Which factor most strongly influences the likelihood of transmission of M. tuberculosis?
A. The type of immune response in the exposed individual
B. The virulence of the transmitted organism
C. The shared environment and duration of contact with an infectious patient
D. The nutritional status of the exposed individual
C
The likelihood of transmission depends on factors such as the shared environment, the intimacy and duration of contact, and the infectiousness of the TB patient, especially sputum smear–positive cases.
What is the role of sputum smear–positive cases in TB transmission?
A. They are less infectious but account for the majority of TB cases.
B. They are the most infectious and primarily responsible for disease spread.
C. They are only minimally infectious but can cause reactivation in latent cases.
D. They are noninfectious but can trigger hypersensitivity reactions.
B
Why are HIV-infected individuals with TB generally less infectious than non-HIV-infected individuals with TB?
A. They produce fewer droplet nuclei during coughing.
B. They lack cavitary disease, which reduces bacillary load.
C. Their immune suppression eliminates transmission risk.
D. They typically have extrapulmonary TB, which is noninfectious.
B
In high-prevalence settings, how many individuals might an undiagnosed AFB-positive TB case infect before diagnosis?
A. 1–5 contacts
B. 3–10 contacts per year, up to 20 total contacts
C. 50–100 contacts per year
D. None, as they are typically noninfectious until symptoms develop
B
Why is the incidence of tuberculosis highest during late adolescence and early adulthood in infected individuals?
A. Poor nutrition during this period
B. Immunologic changes associated with puberty
C. Reasons for this age-specific peak remain unclear
D. Increased risk of reinfection due to high social activity
C
What is the primary difference between primary and secondary (postprimary) tuberculosis?
A. Secondary TB is less infectious than primary TB.
B. Primary TB occurs years after infection, while secondary TB occurs immediately.
C. Secondary TB often involves cavitation and is more infectious.
D. Primary TB occurs only in immunocompromised individuals
C
How does reinfection contribute to the development of active TB in high-prevalence areas?
A. It is the primary mechanism of TB disease in low-prevalence areas.
B. Reinfection is uncommon in areas with high TB transmission.
C. Reinfection leads to the development of active disease in previously infected individuals.
D. It is responsible for less than 5% of active TB cases in endemic regions.
C
In which lung zones is primary pulmonary TB most commonly located?
A. Apical and posterior segments of the upper lobes
B. Middle and lower lung zones
C. Superior segments of the lower lobes
D. Anterior and basal segments of the lungs
B
What is the characteristic lesion formed during primary pulmonary TB called?
A. Caseating granuloma
B. Ghon focus
C. Cavitary lesion
D. Miliary nodule
B
What is the cause of pleural effusion in primary pulmonary TB?
A. Lymphatic spread of bacilli
B. Bacillary penetration into the pleural space from a subpleural focus
C. Hematogenous dissemination of infection
D. Compression of pulmonary vessels
B
What radiographic finding may indicate healed primary TB?
A. Consolidation with air bronchograms
B. Cavitation in the upper lobes
C. Small calcified nodule
D. Reticulonodular pattern
C
What is the most common site of involvement in postprimary (adult-type) pulmonary TB?
A. Middle lung zones
B. Apical and posterior segments of the upper lobes
C. Lower lung zones
D. Superior mediastinum
B
What is the most common origin of postprimary TB in endemic areas?
A. Endogenous reactivation of distant infection
B. Exogenous reinfection
C. Reactivation of latent TB in immunocompromised individuals
D. Recent infection (primary or reinfection)
D
. Which of the following is a hallmark feature of cavitary postprimary TB?
A. Necrotic contents are contained within the lesion.
B. Liquefied necrotic contents are discharged into the airways.
C. Lesions heal by fibrosis without cavitation.
D. Cavities are rarely involved in bronchogenic spread.
B
What is the most common symptom in postprimary pulmonary TB?
A. Night sweats
B. Persistent cough
C. Hemoptysis
D. Weight loss
B
Which hematologic abnormality is commonly associated with postprimary pulmonary TB?
A. Leukopenia
B. Thrombocytopenia
C. Mild anemia and thrombocytosis
D. Pancytopenia
C
Mild anemia.
Leukocytosis.
Thrombocytosis.
Elevated erythrocyte sedimentation rate (ESR).
Increased C-reactive protein (CRP).
What is Rasmussen’s aneurysm in the context of postprimary TB?
A. An aspergilloma forming in an old cavity
B. A dilated vessel in a cavity wall that can rupture
C. A necrotic lymph node rupturing into a bronchus
D. A granuloma forming in the lung parenchyma
B
Typical Chest Radiograph Findings (Immunocompetent Patients):
Upper-lobe infiltrates with cavitation.
Cavitary disease more likely with delayed diagnosis.