Mycobacterium Flashcards
What is a disease caused by mycobacteria?
TB
What is the rate of growth of M. tuberculosis? What does it invade? What is its oxygen requirement?
Slow growing
Macrophages
Obligate aerobe
What are two forms of TB?
primary and secondary
Describe primary TB
mild
starts from the lung
formation of granulomas, followed by caseation
Describe secondary TB
caused by reactivation of dormant organism.
Delayed-type hypersinsitivity reaction to the reactivated org
How does primary TB differ in immunocompromised individuals?
the granuloma/caseation proceeds to miliary TB with dissemination to other body sites, bone marrow, spleen, kidney and CNS
How does the x-ray differ in two forms of TB?
primary - outline, macrophage
secondary - apex, mid lung
What is the Ghon complex?
Granuloma caused by multinucleated cells, fused macrophages, T cell, fibroblast –> caseous necrosis
What is Miliary TB? What type of patients is this seen in?
White nodules, smaller than granulomas. Seen in HIV patients
How are MTB infections transmitted?
aerosols
What is significant about MTB cell wall? What does it do?
Waxes in cell wall. provides resistance to drying and chemicals, germicides
affects permeability of cell - nutrients can’t get in - slow growth
What is used to ID Mycobacteria?
Acid fast stain
What are two main chemicals used in acid fast stain?
Carbolfuchsin
Acid alcohol
What color is Mycobacteria seen as after acid fast stain? What is the reason for that?
Bright red because of the wax that does not get destained with acid alcohol
What is a medium used to ID M. tuberculosis?
Lowenstein-Jensen
Middlebrook 7H10
What component of the acidic wax is toxic?
Mycolic acid (beta-hydroxy fatty acid linked to murein)
Where does MTB grow?
Macrophages and monocytes
What two things allow MTV to escape phagosomes?
- prevents acidification via NH4 production –> no phagosome/lysosome fusion/acidification
- Hemolysin
What cytokine provoked by cell wall components cause lung damage?
TNF-a
TB is associated which group of immuno compromised patients?
AIDS
Patients with AIDS and TB are more likely to develop what?
extrapulmonary disease, lymph nodes, genitourinary CNS
What is the consequence of reduced CD4+ T cell in AIDS/TB patients? Explain the process
no macrophage activation
Macs release IL-12 –> Th1 recruited –> Th1 releases IFN-g –> Mac activation
Without Th1, the activation cannot occur
What specific infection are patients with AIDS susceptible to?
MAI
What is the current therapy for TB/AIDs a combination of ?
Macrolides Rifabutin Ethambutol Clofazimine FQN
What are the four Anti-TB drugs? How long?
Isoniazid (INH) *
Rifampin
Streptomycin
Ethambutol
6 months
Treatment for TB
Anti-TB drugs
Prophylaxis
Vaccine
What is MAI?
faster growing acid-fast bacilli found in macrophages
How does co-infection of MAI occur in AIDS patients?
Fruit in GI of immunosuppresant patients can spread – systemic infection
What is seen in cultures with MAI?
MAC (MAI complex)
- wax, miliary, macs
Can M. leprae be grown in lab medium?
No
How is M. leprae confirmed?
skin test reactivity to lepromin
presence of acid-fast bacilli in skin lesions
What are the two different presentations of M. Leprae?
- Tuberculoid leprosy: milder, self-limiting disease (cell mediated)
- Lepratomous leprosy: severest form (not cell mediated)
Which T cell is involved in Tuberculoid leprosy? what is the infectivity?
Th1
low infectivity
What T cell response is seen in Lepromatous Leprosy? what is the infectivity?
Th2
High infectivity
How does Lepromatous leprosy differ from Tuberculoid in terms of immunity?
Lepromatous is Autoimmune
Due to lack of Th1 response, Lepromatous leprosy is ______ to lepromin.
nonreactive
What is analogous to miliary TB?
Lepromatous leprosy
What is the effect of Lepromatous leprosy?
extensive tissue destruction
CNS damage - schwann cells
Treatment for M. leprae
how long?
Dapsone
rifampin
clofazimine
minimum of 2 years
Why is M. kansasii atypical?
yellow pigmented in presence of light
Who can have M. kansasii?
HIV patients with CD4 count less than 200 cells/ml
How does M. kansasii present?
PPD positive
resembles tuberculosis
Treatment of M. kasasii
chemotherapy with isoniazid, rifampin, ethambutanol
What is the most significant point made in lecture about mycobacterium?
HIV co-infection