Mycobacterium Flashcards
What is the metabolism of M.tuberculosis?
- Aerobic
- Catalase (+)
- Slow growth rate
What is the morphology of M.tuberculosis?
- 40% of total cell dry weight is lipid.
- Composed of mycolic acids.
- Thin rods.
- Non motile.
What is the role of mycosides in the virulence of M.tuberculosis?
- Cord factor
- Sulfatides - inhibit phagosome-lysosome fusion.
- Wax D - acts as an adjuvant
Besides mycosides, what other virulent factors does M.tuberculosis utilize?
- Iron Siderophore - mycobactin.
2. Facultative intracellular growth - Can survive and multiply in macrophages.
Has M.tuberculosis toxins?
Neither exotoxin nor endotoxins. It has lipopolysaccharide, but no lipid A.
What happens in primary TB?
- Asymptomatic
2. Overt disease, involving lungs or other organs.
What happens in secondary TB?
- Pulmonary problems
- Pleural or pericardial lesions
- Lymph node infection
- Kidney
- Skeletal
- Joints
- CNS
- Miliary TB
How do we diagnose M.tuberculosis?
- Acid-fast stain of specimen.
- Rapid culture
- PPD skin test
- IGRA (interferon gamma release assay)
- Chest X ray
- Gene Xpert MTB/RIF (and similar PCR based studies)
What happens in rapid culture of M.tuberculosis?
- Bactec radio metric culture, a liquid broth in a bottle, with radioactive palmitate as a carbon source.
- Mycobacteria grow and use carbon, allowing early detection (1-2 weeks), even before colonies can be seen.
What happens in PPD?
Measure of zone of induration:
>5mm: immunocompromised host.
>10mm: chronic disease or risk factors for exposure to TB.
>15mm: all others.
When do we get false negatives PPD?
In patients with AIDS or malnourished individuals.
What is useful to remember about the virulence of M.tuberculosis?
- Non motile
- No capsule
- No attachment pili
What is the metabolism of M.leprae?
- Catalase (+)
- Grows best at low temperatures
- Phenolase (+) - converts dopa into pigmented product (used for diagnosis).
What is the virulence of M.leprae?
- Non motile
2. Facultative intracellular growth
What happens in lepromatous leprosy?
- Low cell-mediated immunity
- Organisms found everywhere (organs and blood)
- Skin, nerves, eyes and testes involved bilaterally.
What happens in tuberculoid leprosy?
- Intact cell-mediated immunity
- Difficult to isolate M.leprae from skin or blood.
- Skin and nerves involved: 1-2 unilateral superficial lesions.
How do we diagnose M.leprae?
- Can not be grown on artificial media. Only be cultured in certain animals, such as mice foot, pads, armadillos, or monkeys.
- Skin or nerve biopsies - will reveal acid-fast bacilli (lepromatous) or granulomas (tuberculoid).
What is the usefulness of lepromin skin test?
Not in diagnosis, but in positioning of patients on the immunologic spectrum.
What are the common clinical presentations of M.avium complex?
- In AIDS patients –> disseminated infection with fever, weight loss, diarrhea, hepatitis.
- In immunocompetent host –>
a. Upper lung cavitary disease in elderly smokers.
b. Middle and lower lung nodular and bronchiectatic disease in middle-aged female non-smokers. - Lymphadenitis –> in children.
What should you suspect when you see fever of unknown origin in AIDS patients?
M.avium complex.
What is the MCC of non tuberculosis mycobacterial lung disease?
M.avium complex.
What are the common clinical presentations of M.kansasii?
- Pulmonary: upper lung cavitary disease (resembles TB).
2. Disseminated diseased in immunocompromised.
What is the 2nd MCC of non tuberculosis mycobacterium lung disease in the US?
M.kansasii
What are the common clinical presentations of M.abscessus?
- Pulmonary disease
2. Skin, soft tissue, and bone disease
