TB Flashcards
Describe the composition of an acid-fast cell wall and indicate the advantages and disadvantages of this structure for the bacterium.
- Cell Envalope made from:
- Waxes
- Mycolic Acids
- Polysaccharides
- Peptidoglycan (murein)
- Phenolic Glycolipid I (PGL-I) • Lipoarabinomannan (LAM)
- Cell Wall made of:
- Lipoarabinomannan
- Glycolipid
- Mycolic acids
- Arabinogalactan
- Peptidoglycan: only a small amount/single layer
- Acid fast staining b/c of these structures-Don’t stain w/ gram stain
- These structures protect the bacterium from the environment
Mode of Transmission
- Respiratory
- Inhalation of droplet nuclei (< 10 μmdiameter)
- man-to-man transmission
- Ingestion
- Intestinal route via ingestion of M. bovis in contaminated milk and milk products
- animal- to-man transmission
Pulmonary TB – Stage 1
- Inhalation of droplet nuclei- seeding into mid to lower lung
- Bacteria multiply in alveolar spaces
- Bacteria are ingested by alveolar macrophages
- Bacteria are destroyed or
- Bacteria grow in macrophages and kill them
Pulmonary TB – Stage 2
- Logarithmic growth of bacteria inside macrophages
- Arrival of circulating macrophages
- Bacteria spread to arriving macrophages
- Dissemination via infected macrophages into lymphatics and blood stream
- No host defense during first few weeks after infection
Pulmonary TB – Stage 3
- Bacteria growth in macrophages countered by immune response
- Activated macrophages ingest bacteria and destroy them
- Cytotoxic T-cells recognize infected macrophages and destroy
- Formation of granulomas and Ghon complexes (primary lesions) at site of primary infection
Life Cycle:
- Droplets enter the respiratory system and M. tuberculosis taken up by alveolar macrophages
- Macrophage goes to blood
- Becomes a foamy macrophage w/ lipids and blood vessels and lymphocytes surround
- Fibrous cuff forms around the foamy macrophage and the infected macrophages
- Caseum forms in the center of the surrounded mass
- Mass bursts through the airway releasing necrotic granuloma and mycobacterium
Describe the principle underlying the tuberculin test and how the results of the test should be interpreted in normal and AIDS patients.
-Tuberculin Test:
-Intradermal injection of 5 TU PPD-T in 0.1 ml of solution
-Produces wheal 6 mm to10mm diameter
-Reaction is usually read in 48-72 hrs
>5mm positive in:
-HIV infected patient
-Close contact to TB case
-Fibrotic changes on CXR consistent with old TB
-Patients immunosuppression
>10mm positive in:
-Recent immigration from countries w/ high incidence of TB
-IV drug users
-Residents and employees in high risk congregate settings
-Workers in mycobacteria labs
-Clinical Conditions putting at risk
-Children 15mm positive in:
-Persons w/ no know risk factors for TB
-False positive if
-Non- TB mycobacteria
-BCG vaccine
-False Negative
-Anergy
-Recent TB infection
-Very young <6m
-Live virus vaccine
-Overwhelming TB infection
Explain the treatment of tuberculosis.
- Isoniazid
- Rifampin
- Pyrazinamide
- XDR TB = TB whose isolates are resistant to isoniazid and rifampin plus resistant to any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin)
Primary TB
- Infection in nonimmune host
- Presentation: hilar nodes
- Gohn complex affects the lower lobe
- Results:
- heal by fibrosis-Immunity and hypersensitivity (PPD +)
- Progressive lung disease (HIV/malnutrition)-> death
- Severe bactermia- miliary TB-> death
- Preallergic lymphatic or hematogenous dissemination
- dormant tubercle bacilli in several organs
- Reactivation in adult life
Secondary TB
- Reactivation TB
- Fibrocaseous cavitary lestion
- Usually affects upper lobe
- Extrapulmonary TB:
- CNS (parenchymal tuberculoma or meningitis)
- Vertebral body: Pott’s disease
- Lymphadenitis
- Renal
- GI
