Mycobacteria Flashcards
What species causes Tuberculosis
M. tuberculosis
What species causes Chronic lung infection
MAC
M. Kansasii
What species causes fish tank granuloma
M. Marinum
What species causes Buruli ulcer
M. ulcerans
What species causes leprosy
M. leprae
Are mycobacteria aerobic or anaerobic
Aerobic
Can mycobacteria be destained by acid and alcohol
No
Shape of mycobacteria
bacillus
Define bacillus
Rod-shaped, Gram-positive and aerobic
Where are mycobacteria found
Inside macrophages
Relative growth rate of mycobacteria
Slow REPRODUCTION
Slow GROWTH in Human
Slow GROWTH IN CULTURE
Slow RESPONSE TO TREATMENT
4 aspects of Koch’s postulates
- Bacteria should be found in all people with disease
- Bacteria should be isolated from the infected lesions in people with the disease
- Pure culture inoculated in a person should show symptoms of the disease
- Same bacteria should be isolated from the intentionally infected individual
Why are mycobacteria resistant to gram-stain
High lipid content with mycelia acids in the cell wall causing them to become v-shaped
What stain is needed for acid fast bacilli
Ziehl-Neelsen stain (AFB)
What are the three elements of the Ziehl-Neelsen stain
- Carbol fuchsin
- Acid Alcohol
- Methylene Blue
How much AFB is needed per ml sputum
10,000 AFB
Difference between Fluorochrome stains and AFB stain
Fluorochrome stains aid screening at lower power objective lenses
What colour does the Ziehl-Neelsen stain give when the test is positive for acid-fast bacilli
Red/Pink
How do we analyse nucleic acid of mycobacterium
PCR
Produces rapid results
What bacteria is PCR used for diagnosis and why
TB
Fast and specific
How do mycobacteria cause disease
- Acid fast bacilli are phagocytose and placed in phagolysosome
- Bacteria adapts to intracellular environment and withstands phagolysosomal killing
- Escapes to cytosol
- Host tries to kill mycobacterium via microbicidal molecules
- These assist in digestion and degradation by bacterial proteases
- Degraded into antigens for T cell presentations
Ignored by immune system
Describe the normal immunological process that take place following invasion of a pathogen
- CD4 cells produce INF-gamma
2. IL-12 further stimulates the release of INF gamma
What are granulomas
Lesions that arise in response to containing mycobacteria
How does mycobacteria granulomas form
- Macrophages become epithelioid cells
- Macrophages fuse together to form giant multinucleate cells
- T cells infiltrate the granuloma
- Central tissues necrose to form caveating granuloma
- Granuloma prevents nutrients from entering - starving the mycobacteria forming cavities
Why is a granuloma dangerous for a bacteria and how is this overcome by mycobacteria
- Nutrients can’t enter the granuloma
2. Mycobacteria goes into dormant state (TB) until conditions are better
Role of CD8 cells
Lyse infected macrophages
Why would we get a disorganised granuloma
- TNF neutralisation causes cells within the granuloma to no longer be as tightly clustered
In what individuals is TB activation with a greater risk
- Age
- Malnutrition
- Intensity of exposure
- Immunosuppression
Why does M. tuberculosis cause activation of the immune system
Lipid-rich cell wall stimulates T-cell response 3-9 weeks after exposure
Positive effects of immunological stimulation from TB
- Macrophages kill mycobacteria
- Containment of infection
- Granuloma
Negative effects of immunological stimulation from TB
- Hypersensitivity Type 4
- Skin lesions
- Eye lesions
- Swelling of joints
How can immunological reactivity to TB be measured
Tuberculin skin test
INF gamma release assays
Describe the tuberculin skin test
- Intradermal injection of purified protein derivatives induce skin swelling and redness
What is Tuberculoid leprosy
- Associated with type 4 hypersensitivity and granulomata
- Paucibaccillary lesions with low mycobacteria no.
- Tissue damage
- Involves Th1 CD4 cells and IFN-gamma and TNF-alpha
What is the lepromatous leprosy
- Lesions full of bacilli but no granulomata
- Skin lesions
- Predominant Th2 biased CD4 T-cell responses with IL-4,5,10 production
What are the three categories of leprosy
- Tuberculoid
- Lepromatous
- Borderline
Tuberculoid vs Lepromatous leprosy
Tuberculoid - immune response is good and only few lesions + mildly contagious
Lepromatous - Immune response poor + affects skin, nerves organs + widespread lesions + more contagious
Where do bacilli settle in primary TB
- Apex of the lungs
How are bacilli removed from apex in primary TB
Lymphatics to hilar lymph nodes
Why do bacilli settle at the apex in primary TB
- More air and less blood supply thus few defending white cells
What is the primary complex
Granuloma
Lymphatics
Lymph Nodes
Why is caseous material coughed out from the lung in pulmonary TB
- Cell-mediated immunity and necrosis = abscess of bacilli which is coughed up
Can TB spread beyond the lung
Yes:
Pleura
Bones
Genito-urinary tract
What is latent TB
- Cell mediated response from T-cells
2. Primary infection is contained but cell-mediated immunity persists
What can be seen on an X-ray in an individual with latent TB
Normal chest
How can we detect Latent TB
Tuberculin skin test
When does pulmonary TB take place
Following primary TB
