Mycobacteria Flashcards
Give three examples of mycobacteria:
1- M. tuberculosis
2- Atypical mycobacteria
3- M. leprae
Explain the acid fast staining procedure
1- smear sample on glass slide 2- Dye with Carbofuchsin 3- Steam over boiling water 4- Cool and decolorize with Alcohol 5- Rinse with water to stop decolorization 6- Counterstain with methylene blue 7- Rinse 8- Blot dry and examen
What color do acid fast bacteria show up on an acid fast stain?
pink
What is a distinctive feature of acid fast bacterial cell wall?
mycolic acids and arabinogalactan
What type of respiration do mycobacteria undergo?
obligate aerobes
Do mycobacterium grow in culture?
M. tuberculosis can, but grows VERY slowly!
M. leprae cannot grow in cultre
What does M. tuberculosis need to grow in culture?
Time and special nutrients
Is M. tuberculosis an intracellular or extrcellular pathogen?
Both
Where is M. tuberculosis drug resistance encoded?
plasmids (easy transfer)
What are three main virulence factors of M. tuberculosis? And what is the function of each factor?
1- Mycolic acid (helps evade the immune system)
2- Phosphatides (stop necrosis)
3- Cord factor (contributes to virulence)
Describe the ID of M. tuberculosis:
Extremely low ID50. Less than 10 organisms needed for infection
What is the pathogenesis of TB?
1- Inhalation of infected particles
2- Alveolar macrophages phagocytose the bacteria
3- Bacteria prevents the fustion with a lysozome
4- Bacteria uses macrophage as a trojan horse
5- Bacteria can proliferate in macrophage and continue to cause disease (systemic)
What types of symptoms can M. tuberculosis cause when they proliferate in macrophages?
1- Exudative lesions
2- Granulomatous lesions
3- Tubercule
4- Reactivation lesions
What are exudative lesions?
These are typically found in the lungs/ initial site of infection with TB. It is an acute inflammatory response of a Ghon complex.
What is a ghon complex?
exudative lesion and draining lymph nodes
What is a tubercule?
this is an older granuloma that is surrounded by fibrous tissue and has a central caseation necrosis
How does a tubercule heal?
fibrosis and calcification
What allows lesions to be reactivated?
immunosuppression or infection with Measles, varicella, or pertussis
Where can reactivation lesions occur?
neck, kidney’s, brain, spine, lower lung
How is an infection with M. tberculosis controlled by the immune system?
cell mediated immunity. CD4 helper t cells activate some infected macrophages to kill intracellular bacteria and CD8 t cells lyse other infected macrophages
What is the result of the cell mediate immune response to tuberculosis infection?
caseating granuloma (latency)
What is an important factor in maintaining latency?
TNF-alpha
What are the different presentations of TB infection?
1- Classic active pulmonary TB 2- TB scrofula 3- GU TB 4- CNS TB 5- Skeletal TB 6- GI TB 7- Miliary TB 8- TB memingitis
What is indicative of classic active pulmonary TB?
cavity formation in the lung, fever, night sweats, weightloss, cough
What is TB scrofula and what is indicative of this condition?
This is reactivation of TB in a lymph node
Symptoms include a painless, enlarging, or persistent mass. Usually the cervical lymph nodes.
What is the most common etrapulomary site of TB infection? And what are the symptoms?
GU Track
Reaches the kidneys but can be latent for 20 years
How is CNS TB diagnosed?
MRI and spinal tap
What are the two main manifestations of skeletal TB?
joint arthrtitis and potts diease
How does pott’s disease present?
back pain, stiffness, paralysis or lower extremities
What is a major symptom of GI TB?
obstruction or hemorrhage of the iliocecal region
What is miliary TB?
Hematogenous spread of TB throughout the body. There are many tiny NON-calcified foci of infection in the lungs.
When is miliary TB most likely to occur?
After a primary infection, rather than during reactiviation
What is a diagnostic sign of TB meningitis?
Brudziniski’s sign (cranial nerve palsies)
What is the difference between a PPD for TB and one for leprosy?
TB tests exposure whereas leprosy tests you immune response
What are the typical characteristics of atypical mycobacteria?
Acid fast wall, do not cause TB or leprosy, usually environmentally acquired
How many groups of atypical TB is there?
4 main groups
What is the reservoir for M. leprae?
Humans and armadillos
What is the pathogenesis of M. leprae?
unclear transission method with an extremely long incubation period.
What type of cells does M. leprae cause an intracellular infection?
skin histocyes, endothelial cells, schwann cells
what are the two forms of leprosy? What is the difference between the two ?
Tuberculoid leprosy and Lepromatous leprosy
Tuberculoid is a strong CMI response with few bacilli. There is typically immunogenic nerve damage and granuloas form
Lepromatous leprosy is a poor CMI response with a lot of bacilli. Nerves are damaged by bacteria and foamy histocytes form
