Mycobacteria Flashcards
Mycobacteria (stain)
Gram-positive structure but stains acid-fast (carbol fuchsin stain), mycolic acid in cell envelope, grow very slowly
M. tuberculosis characteristics (where does it grow, metabolism)
Facultative intracellular, strictly aerobic
M. tuberculosis pathogenesis
Exposure, infection (bacteria taken up by alveolar macrophages), disease (spreads to local lymph nodes -> dissemination)
How does host immune response control TB?
Cellular immune response (delayed type hypersensitivity)
What increase risk of reactivation in TB?
HIV infection, advanced age, alcoholism, malnutrition, immunosuppression
TB Histopathology
Macrophages undergo transformation as try to contain bacteria, lymphocytes surround macrophages, fibrous layer forms around macrophages (granuloma), necrosis of center of granuloma (caseating granuloma)
M. tuberculosis bacterial factors
Mycolic acid and lipid, slow growth leads to antibiotic resistance (antibiotics work best against rapidly dividing bacteria)
Tuberculosis 2 types
Pulmonary TB: Chronic productive cough, cavitation in the apex of the lung (higher concentration of oxygen in upper lobes of lung)
Extrapulmonary TB: Particularly common in HIV-infected patients, referred to as Pott’s Disease when involve vertebrae of back
M. bovis
Infect cattle, acquired by drinking unpasteurized milk, causes tuberculosis
Miliary TB
Widely disseminated TB not controlled by the immune system, systemic infections, organism in vasculature, not airways
“Snowstorm” pattern
TB Diagnostic Tests (Including active disease)
Tuberculin skin testing, Interferon-gamma release assays
Active disease: Acid-fast staining of sputum, Gold standard: Growth from clinical specimens, Nucleic acid amplification tests (NAAT)
TB Treatment (Latent TB)
Small loads of organisms in body - Rifampin, isoniazid
TB Treatment (Active TB)
High bacterial loads - risk of antibiotic resistance
Usually treated with multiple drugs (4 -> 2 drugs for 6 months)
Rifampin
Isoniazid
Pyrazinamide
Ethambutol
MDR TB Definition
Multiple-drug-resistant
Resistance to rifampin and isoniazid, results from noncompliance
XDR TB Definition
Extensively drug resistant
MDR-TB with additional resistance to quinolones and at least one 2nd line injectable agent (amikacin, capreomycin, kanamycin)
TB Prevention
BCG vaccine derived from attenuated strain of M. bovis
Respiratory isolation for patients with AFB-positive sputum
M. leprae (where does it grow, what does it cause)
Obligate intracellular pathogen, cause of leprosy (Hansen’s disease)
M. tuberculosis versus M. laprae (where do they grow)
Facultative versus obligate intracellular
M. laprae DP
Human-to-human transmission, directly kill Schwann cells
2 extremes of leprosy
Tuberculoid (intense cell-mediated immune response, very few bacteria in tissues, Th1 response)
Lepromatous (no cellular immune response, many bacteria present, Th2 response)
Leprosy CD
Hypopigmented skin lesions (cooler tissues, often raised along edges), affects peripheral nerves
Interesting manifestations - leonine facies, saddle-nose
Leprosy DLT
Does not grow on artificial media or cell culture
Cultured in armadillos
Extremely slow grower
Diagnosis made by histologic examination of a biopsy of a skin lesion
Leprosy treatment
Dapsone and rifampin +/- clofazimine for 6-12 months
MAC (what does it cause)
M. avium-intracellulare complex
- Disseminated and GI disease in immunocompromised patients
- Pulmonary disease in elderly and individuals with cystic fibrosis
M. kansasii (what does it cause)
Pulmonary infections similar to TB
M. abscessus and M. fortuitum (what does it cause)
Rapid-growers
Pulmonary, skin, soft tissue infections
M. marinum (what does it cause)
Soft tissue infections following contact with fish tanks, fish, salt-water, spread up lympathics
Know for boards: Cuts finger while cleaning aquarium, develop soft tissue infection
M. marinum
TB Signs and Symptoms
Fever and chills, night sweats, weight loss
What medium does TB grow on
Lowenstein-Jensen medium
M. tuberculosis virulence factors
Cord factor, sulfatides (prevent fusion with lysosome)
TB Reactivation symptoms
Cough, night sweats, hemoptysis
Reactivation can affect which systems
Skeletal system - Pott’s disease
Cavitary lesion - Tuberculoma
What results after primary TB infection
Ghon complex
