Mycobacteria Flashcards
What is the background to mycobacteria?
- Non-motile
- non-spore forming
- aerobic or microaerophillic
- Gram Positive but hard to stain due to abundant lipid
What does the thick layer of mycolic acids contribute to?
Environmental and antimicrobial resistance
When is m.avium most commonly seen?
Most commonly causes mycobacteriosis in birds
Where is m.bovis most commonly seen?
Persists in soil, remains infective for weeks
* high doses are required for oral transmission
What is the normal pathogenesis of mycobacterium?
- Mycobacterium are phagocytosed by alveolar macrophages
- they prevent fusion of the phagosome with lysosomes
- they replicate and persist within macropahges
What happens if mycobacteria is not phaocytosed immedietly?
- release of TNF-a, IL-12 and cytokines to recruit other macrophages and lymphocytes
- IL-12 drives a type I immune response
What is the function of the tuberculoid granuloma?
- It prevents spread to other sites and other hosts
- Cell mediated response kills infected macrophages and forms the caseous centre
What is the clinical presentation of mycobacterium bovis?
Most animals that are infected never develop clinical signs- they either eliminate or contain the bacteria
How would you use an intradermal skin test to test for mycobacterium bovis?
Purified protein derivatives can produce delayed type hypersensitivity reactions in a sensitized animal
What is the function of glycolipids in mycobacteria?
they induce a macrophage response and prevent lysosomal degredation
What is tthe purpose of the granuloma formation during infection?
- helps contain the infection
- prevents spread
What is the downside to the cell mediated response when the infection is large?
may cause extensive tissue damage
What does the mycobacterium tubercle look like?
- Circumscribed, often encapsulated
- Pale, yellow-white nodule
- Granulomatous inflammation with central caseous necrosis
- large ones may liquefy
- Fibrosis increases over time
What is the most common infection for humans?
M.Tuberculosis
What is the most common route of infection for mycobacterium bovis?
Inhalation is the most common, this causes lesions in the lungs, airways and associated lymph nodes
When does oral infection of mycobacterium bovis occur?
Occurs when there is coughing up and swallowing of sputum from infected lungs
How does respiratory mycobacterium bovis occur?
- Tubercles spread into airways and release bacteria that can spread within the lung/ be coughed up and swallowed
- they can also erode into the pleura and spread in the pleural cavity
What are the differences in lesions between cervids and cattle?
Cervids
* develop superficial lymphadenitis that drains to the skin surface
* Disease progresses faster
* they are less able to contain the infection and more susceptible
* suppurative inflammation is more prominent than caseous necrosis
What do mycobacterium bovis lesions look like in carnivores?
- Discrete tubercles are uncommon
- instead they form granulation tissue
What do mycobacterium bovis lesions look like in cats?
- nonhealing wounds with central necrosis
- low numbers of bacteria differentiate from feline leprosy
What do mycobacterium bovis lesions look like in dogs?
rapid dissemination through bronchi, causing tuberculous bronchitis
Why is M.bovis hard to culture?
Culture takes a long time due to slow growth (4-6 weeks)
How are humans likely to be infected with M.bovis?
- Immunosuppression
- Contaminated Milk
- Aerosol or Wound Infections are also common
What are the 4 routes of infection for m.bovis?
- Inhalation
- Oral Infection
- Transplacental
- Percutaneous
