Mycobacterial Infections Flashcards
Mycobacteria
Cell walls contain large amounts of lipid- Acid Fast
Grow more slowly, chronic disease, slowly progressive disease
Replicate w/in monocytes/macrophages, elicit granulomatous inflammation.
High lipid content of cell wall inhibit the fusion of phagosome w/ lysosome
Mycobacteria tuberculosis hominis
Chronic, communicable disease in which the lungs are the primary target.
Can be reactived- most common in the elderly
M. tuberculosis bovis (rare)
Drinking unpasteurized milk from infected cows
TB Infection
The organism is growing in a person, whether or not there is symptomatic disease
Active TB
Denotes the subset of TB infections manifested by destructive symptomatic disease
Primary TB
Occurs on first exposure to the organism and can pursue either an indolent or aggressive course
Replicated within alveolar macrophages, initiate a hypersensitivity** & cell-mediated immune response that eventually contains the infection. Infected macrophages present mycobacterial ag to Tcells. Clones of sensitized Tcells proliferate, INF-y produced & activate macrophages, increasing lytic enzymes, which damage host tissue
*characteristic cheese-like “caseous granuloma “consistency
Ghon focus-lung lesion
90% healthy adults self-limited
Secondary TB
Develops long after a primary infection, mostly due to reactivation of a primary infection. Can also be produced by exposure to exogenous organisms and is always an active disease.
T cell mediated immune response leads to tissue necrosis and production of tuberculous cavities- which are optimal for multiplication, surrounded by granulomatous response.
*Untreated is fatal
Progressive Primary Tuberculosis
Found in immunologically immature or compromised subjects.
Granulomas are poorly formed or not formed at all & infection may progress at the primary site in the lung.
Ghon focus gets larger and may even erode the bronchial tree, middle lobe syndrome
Miliary TB
Infection disseminates to produce multiple, small yellow, nodular lesions in several organs.
Lesions ressemble millet seeds
M. leprae
Leprosy (Hansen Disease)- chronic, slowly progressive, destructive process involving peripheral nerves, skin and mucous membranes.
**Cannot be cultured in artificial media
Like to replicate in areas below normal body temp
Mode of infection is unclear.
Anergic patients: have little or no resistance and develop lepromatous leprosy
Hyperergic patients: highest resistance, contract tuberculoid leprosy
Tuberculoid Leprosy
Characterized by a single lesion or very few lesions of the skin, dermal granulomas (lack caseation)
Sensory deficit due to swollen nerve fibers infiltrated by lymphocytes
Lesions cause minimal disfigurement and are not infectious
Lepromatous Leprosy
Exhibits multiple tumor like lesions
Nodular or diffuse infiltrates of foamy macrophages contail myriad bacilli.
Dermal infiltrates expand slowly to distort and disfigure.
Mycobacterium avium
Mycobacterium intracellulare
Similar species that cause identical disease MAI complex, causes 2 types of disease
Found in soil, water and fod
MAI Granulomatous Pulmonary Disease
Found in immunocompetent & many suffer preexisiting pulmonary disease (COPD)
Resembles TB that progesses more slowly
Pulmonary nodules and cavities and caseating granulomas.
MAI Disseminated Infection in AIDS
In AIDS the depletion of helper Tcells cripples immune response that normally prevents MAI.
Phagocytes cannot kill, this is where MAI replicates
Expanding nodular lesions due to recruitment of macrophages that keep getting filled w/ MAI. Progressive small bowel involvement
