TB and Atypical Mycobacteria Flashcards
Who discovered TB and when?
Dr. Robert Koch March 24th
The close relatives of M.Tuberculosis
- M.bovis (in humans and bovines)
- M. africanum
Explain the importance of the cell wall of M. tuberculosis
- Contains long chain fatty acids and waxes that is an important virulence factor. The waxy walls allow it to survive when engulfed by macrophages
- Structural importance: rigidity
3.Can’t be stained with normal gram staing methods and requires an acid fast stain
Why is TB difficult to cultivate in the lab?
1Its slow growing with a generation time of 15-20 hrs
- Obligate aerobe (low Os conditions)
How is TB spread?
In droplets through viral shedding : coughing sneezing
What make TB easily transmissible through the air?
-Droplet nuclie
-10um particle size
-stay suspended in air
-travel lower down the airway due to size
What is the infectious dose of Tb?
1-10 bacilli
Tb is contagious but not easy to acquire. What is necessary to acquire tb?
-Prolonged exposure
8hrs/day for up to 6 months
-Significant exposure
Crowded close communities: school, prisons, families, boarding houses
Who are more likely to spread tb?
Those with a higher bioburden
-immunocompromised
-lung disease patients
What are the steps to the prepathogenesis of tb?
- Source case
- Aerosolization
- Airborne survival
- Inhalation
What are the steps for the pathogenesis of TB
1,Inhaled aerosols
2. Engulfed by alveolar macrophages
3 Local lymph nodes
4. Primary complex (Ghon’s focus + draining LN)
5. Initial Containment of infection
6. Latent infection
7. Heals self or Post primary tb/Reactivation
Diagnostic test for TB in the lungs
- positve TST (tb skin test) and IFN test (interferon gamma test)
- Chest xray abnormal
- Positive sputum smears
- Symptoms: Cough, fever, weight loss
What is the disadvantage of using an IFN test?
This would test positive for both latent and active tb and does not distinguish between
Features of Primary Tb
- asymptomatic
-Ghon’s focus/ Primary complex
-limitted cell mediated immunity
-Occasionally miliary
-Erythema nodosum
Risk factors for Reactivations
-Immunosuppression (HIV, chemo patients)
-Alcoholism
-Chronic illness (diabetes, chronic kidney disease)
-malnutrition
-old age
Where can TB be located outside of the lungs?
Larynx
Lymph nodes
Pluera
Brain
Kidneys
Bones and joints
Genital
Steps for the clinical approach with a probable tb case
- High index of suspicions
- Suggestive symptoms w/ a detailed history
- Investigations
4.Treatment
5.Preventing onward transmission
Symptoms of Pulmonary TB
Fever
Night sweats
Weight loss and anorexia
Tiredness
Cough
Breathlessness (pleural effusion)
Abnormal CXR
What are the four types of investigations done on TB
- Radiology
- Microbiology
- Immunology
- Histology
Abnormalities in a CXR when TB is suspected
Patchy consolidation
Cavitation usually with consolidation in the apex of the lung
Pleural effusion
Solid media used to inoculate tn
LJ slopes (Lowenstien Jensen)
Liquid Media for TB inoculation
MGIT: Mycobacteria Growth Indicator Tube
Pros of LJ slants compared to MGIT liquid
-shorter incubation time (2-6 weeks)
