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What are the general characteristics of mycobacterium
- aerobic
- non spore
- non motile
- rods
- difficult to grow in culture
- arrangement may be in cords: mediated by cord factor
- slow growing
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what is significant in the DNA of mycobacterium
high G+C content in DNA making it more thermostable
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what type of specialized medium does mycobacterium tuberculosis grow in
- lowenstein jensen (green) medium
- contains inhibitory malachite green dye
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mycobacterium cell wall is rich in and typically seen in what kind of stain
- lipid rich: full of mycolic acids
- "weak gram (+)"
- strong acid fast
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what is the significance of the lipid rich mycolic acid cell wall of mycobacteria?
resistant to; antibiotics, disinfectants, detergents, host immune response
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How are proteins in mycobacterium used as a diagnostic tool
antigens on cell wall can be extracted and purified as purified protein derivatives (PPDs) to measure exposure to M. Tuberculosis
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what is cord factor in mycobacterium
- modified mycolic acid found in the surface of mycobacteria
- a virulence factor that prevents phagosome lysosome function
- causes "cord" arrangement of cells
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what are the 4 mycobacterium classified as mycobacterium tuberculosis complex (strictly pathogenic)
- M. tuberculosis
- M. leprae
- M. Africanum
- M. Bovis
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what are the 4 mycobacteria classified as slow growing non tuberculous and are usually pathogenic
- M. avium complex
- M Kansasii
- some strains are yellow
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what are the 5 bacteria classified as rapidly growing nontuberculous mycobacteria
- M. abcessus
- M. fortuitum
- M. Chelonae
- M. Smegmatis
- M. Gordonae
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what are the characteristics of M. Tuberculosis that makes it pathogenic
- lipid rich cell wall: resistant to antibiotics
- slow growth
- life long infection can be dormant/active
- intracellular pathogen and cord factor: makes bacteria avoid being phagocytized
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what structure is formed from M. Tuberculosis infected cells as an inflammatory response
- granuloma: organized collection of tightly clustered macrophages- including immune cells and collagen that is walled off from bacteria.
- may be necrotic
- bacteria may survive inside granulomas and reemerge if the immune system becomes compromised
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what are the type of granulomas
- caseous
- necrotizing: associated with M. Tuberculosis
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what is the size of granulomas when there are few M. Tuberculosis cells
- granuloma is small
- infection can be cleared with minimal tissue damage
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what is the size of the granuloma when there are a lot of M. Tuberculosis cells
- large (caseous) granulomas
- encased in firbin/collagen that protect bacteria from macrophage killing
- bacteria may be dormant when not cleared, then will turn active if immune function decreases
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describe the cycle of how M. Tuberculosis can be latent and reactivate
- M. tuberculosis bacteria becomes encased in granulomas that protects the bacteria from macrophage. This attributes to dormant stage, consisting of 90-95% of infections.
- once bacteria reactivates due to decreased immune function, bacteria can spread and tissue damage occurs. Patients are contagious at this stage
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what are the reservoir of M. Tuberculosis
- disease is spread through person to person by respiratory droplets
- 1/3 of world's population is infected
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what are the populations at greatest risk for disease
- immunocompromised patients
- drug/ alcohol abusers
- prisoners
- homeless
- people exposed to diseased patients
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what are the 2 resistant M. tuberculosis strains
- MDR TB: multi-drug resistant M. Tuberculosis
- XDR TB: extensively drug resistant to at least one second line drug. Potentially untreatable
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What is tuberculosis
- restricted to lungs in immunocompromised patients
- can involve any organ if bacteria disseminates
- nonspecific symptoms: malaise, weight loss, cough, night sweats
- primary disease: cavitation (holes) in alveoli.
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what are the laboratory techniques used to diagnose TB
- specimen: sputum
- radiographic evidence of lung infection
- positive skin test
- microscopic/ culture based evidence
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how is M. Tuberculosis treated?
prolonged treatment with combination of INH, ethambutol for 2 months followed by INH, rifampin for 4-6 months
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what are the disease symptoms of mycobacterium leprae
- leprosy
- tuberculoid (paucibacillary) leprosy
- lepromatous (multibacillary leprosy)
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how is leprosy transmitted
- person to person contact
- inhalation
- skin contact
- incubation may be as long as 20 years after infection
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what is tuberculoid leprosy
- induces strong immune reaction: cytokine production, phagocytosis
- hypopigmented skin macules
- peripheral nerve damage at site of skin lesion
- low infectivity
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what is lepromatous (multibacillary) leprosy
- serious skin disease with skin lesions, nodules, plaques, thickened dermis
- highly infectious
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how is lepramotous leprosy treated
rifampicin, dapsone, for at least 12 months
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how is tuberculoid leprosy treated
rifampicin and dapsone for 6 months
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leprosy is endemic in what areas
- not as widespread
- in india, brazil, madagascar
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what are the two species of mycobacterium avium complex (MAC)
- M. avium
- M. intracellulare
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how is MAC (mycobacterium avium complex) acquired
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who are the patients at greatest risk for M. Avium complex
- AIDs
- those with long standing pulmonary disease
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what is the clinical disease associated with M. Avium complex for immunocompetent patients
- chronic localized pulmonary disease
- "lady windermere syndrome"
- slowly evolving cavitary disease
- solitary pulmonary nodule
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what are the clinical diseases with associated with M. Avium complex for immunocompromised patients
disseminated disease, affecting all organs and impairing normal organ function
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what does IFN-y do
activates macrophages, thus increases intracellular killing of M. Tuberculosis cells
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what does TNF-a do
stimulates production of nitric oxide, which increases intracellular killing of bacterial cells
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what are the cytokines released by macrophages and T cell in response to M. Tuberculosis infection
- macrophage: IL-12, tumor necrosis factor alpha (TNF-a)
- T cell: IFN-y (gamma)
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what are the tests for mycobacterium to diagnose?
- mycobacterial antigen skin test (PPD)
- Measuring IFN-gamma by T cells in whole blood
- acid fast bacteria
- truant fluorochrome method: most sensitive
- Mycobacterial cultures: ex] MODs, special egg based agar, antimycobacterial
- PCR: used when culture is not available or microscopy is inaccurate
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