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102 Cards in this Set
- Front
- Back
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What are mycobacteria?
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Acid-fast, long, slender, nonmotile, nonspore-forming, filamentous rods.
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What are the oxygen requirements of mycobacteria?
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Obligate aerobes.
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What test distinguishes mycobacteria from the majority of other bacteria?
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Ziehl-Neelsen stain
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Why is the Ziehl-Neelsen stain used on mycobacteria?
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Mycobacterium spp. contain a complex lipid coat, they are difficult to stain with Gram stain.
Furthermore, once stained, mycobacterium retain the dye and do not decolorize easily, even with acid, hence they are "acid-fast". |
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How do mycobacteria appear?
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As red rods growing in a cord-like fashion.
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What property accounts for the appearance of mycobacteria?
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High (60%) lipid content of mycobacterial cell walls.
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What is the name of the branched, long-chain fatty acids of the mycobacteria cell wall?
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Mycolic acids
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What are two major Mycobacterium species that cause disease in humans?
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M. tuberculosis
M. leprae |
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What are four minor species of mycobacterium?
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M. avium-intracellulare (MAC)
M. bovis M. kansasii M. scrofulaceum |
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What type of organism is M. tuberculosis?
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Strictly aerobic, acid-fast, intracellular, filamentous rod.
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Which cells do M. tuberculosis show tropism for?
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Macrophages (cells of the reticuloendothelial system)
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What are two mechanisms employed by M. tuberculosis to evade host cell defenses?
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1) Pathogen resides within intracellular vesicles called phagosomes
2) Encodes proteins that prevent fusion of phagosomes wiht lysosomes. |
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What form of immunity is important in fending off M. tuberculosis?
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Cellular immunity
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Why is cellular immunity important in regards to m. tuberculosis?
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Because M. tuberculosis is an intracellular organism.
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Is there an antibody response to M. tuberculosis?
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YES
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Is the antobody response to M. tuberculosis protective?
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NO
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Why isn't the antibody response to M. tuberculosis protective?
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M. tuberculosis are intracellular pathogens that are protected from antibody activity.
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What are five complex lipids and factors that contribute to the hardiness and virulence M. tuberculosis?
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1) Mycolic acids, which enable acid-fastness
2) Wax D, which enhances immunogenicity 3) Phosphatides, which result in caseous necrosis 4) Cord factor, which correlates with virulence 5) Arabinogalactan, which is a cell wall component (M. tuberculosis produces neither exotoxins or endotoxins). |
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How long must M. tuberculosis be cultured for growth to occur?
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6-8 weeks on solid media because it is an extremely slow-growing organism.
There is a new, faster liquid media in which growth occurs in 2-4 weeks. |
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Which is the special culture medium for M. tuberculosis?
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Lowenstein-Jensen agar
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how is M. tuberculosis transmitted?
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Respiratory aerosol
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Why is person-to-person transmission common with M. tuberculosis?
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It can persist in the environment for prolonged periods, partly because the organism is resistant to desiccation.
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What is the reservoir for M. tuberculosis?
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Humans
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What percentage of the world's population is infected with M. tuberculosis?
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33%
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What is the overall percentage of developing reactivation disease after M. tuberculosis infection?
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10%
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When is the risk for reactivation of M. tuberculosis the greatest?
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In the first 2 years after primary infection?
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What is the overall percentage of developing reactivation disease after M. tuberculosis infection in patients with acquired immune deficiency syndrome (AIDS)?
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33-50%
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How does the yearly percentage of M. tuberculosis correlate to developing reactivation disease?
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Increases 10% annually
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What are the possible clinical manifestations of tuberculosis?
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1) Primary disease or initial host infection
2) Secondary disease or reactivation tuberculosis 3) Granuloma formation 4) Granuloma rupture with dissemination. |
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What is the primary infection of M. tuberculosis?
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An infection, usually asymptomatic, often confined to the lungs and occurring after the first exposure to M. tuberculosis.
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Where is the site of primary tuberculosis infection?
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Usually the lower lobes of the lung.
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What is the reactivation tuberculosis?
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A secondary infection resulting from reactivation of dormant M. tuberculosis that persisted in inactive primary lesions.
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What causes reactivation of tuberculosis?
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Age
Malnutrition Other causes of decreased cell-mediated immunity. |
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Where is the site of secondary tuberculosis infection?
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Usually the upper lobes of the lung.
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Why does tuberculosis secondarily infect the upper lobes of the lung?
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It prefers the higher oxygen tension found there.
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What is a granuloma?
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A central area of multinucleated giant cells (macrophages that eventually necrose and fibrose, surrounded by a rim of epithelioid cells
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What is another name for granuloma?
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Tubercle
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Why does the body form granulomas?
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To attempt to sequester teh infectious process.
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What type of necrosis is seen inside a granuloma?
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Caseous necrosis
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What is caseous necrosis?
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A combination of liquefaction and coagulation necrosis resembling cottage cheese
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What is a fibrosed granuloma called?
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A Ghon complex, visualized as a solitary nodule on chest x-ray.
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What are the clinical manifestations of a ruptured granuloma?
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Localized pulmonary involvement (chronic pneumonitis)
Disseminated systemic involvement |
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Why does a ruptured granuloma cause these diseases?
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Spread of infectious, caseous material
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What is miliary tuberculosis?
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Disseminated tuberculosis in which multiple organs are seeded with small M. tuberculosis tubercles that resemble millet seeds.
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What are four extrapulmonary manifestations of miliary tubercuosis?
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1) Osteomyelitis
2) Meningitis 3) Intestinal infection 4) Erythema nodosum |
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What virus predisposes individuals to reactivating tuberculosis?
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HIV
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When are HIV patients most susceptible to reactivating tuberculosis?
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When their CD4 count drops below 500.
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Why are HIV patients susceptible to developing tuberculosis?
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Defective cell-mediated immunity.
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What test is uesd to screen for exposure to M. tuberculosis?
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Purified protein derivative (PPD) test
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Does a positive PPD test indicate active disease?
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NO
PPD tests detect prior infection or exposure to M. tuberculosis, NOT active disease |
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What are exampes of a positive PPD test not caused by active disease?
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History of vaccination, as well as for patients born in certain other countries.
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What is measured when evaluating a PPD test?
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Diameter of induration, or skin elevation, at the injection site.
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What should not be measured?
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Diameter of erythema
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What type of reaction is responsible for induration?
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Delayed (type IV) hypersensitivity
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Under what conditions can a PPD test be positive?
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1) Exposure to M. tuberculosis
2) Atypical mycobacteria present |
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What criteria are used for determinig a positive PPD?
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1) >15mm of induratin is considered positive in those without risk factors
2) >10 mm is positive for those with risk factors (homeless, immigrants from high-risk countries, health care workers) 3) >5mm is positive in those with defective cell-mediated immunity (AIDS patients, or close contacts of those with active TB) |
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Under what conditions can a PPD test be negative?
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1) No previous exposure to M. tuberculosis.
2) Exposure withing 4-6 weeks of PPD test (it takes this long to mount an immune response) 3) Anergy (defective cell-mediated immunity) |
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How can a negative PPD be distinguished from anergy?
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By placing a common allergen on the other arm when admistering a PPD.
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What are the most common symptoms of tuberculosis?
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Fatigue
Night Sweats Weight loss Cough Hemoptysis (90% of M. tuberculosis infections are asymptomatic). |
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What three laboratory tests are used to diagnose M. tuberculosis infection?
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1) Acid-fast staining of sputum
2) PCR amplification of m. tuberculosis RNA/DNA 3) DNA probes |
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What are two major obstacles in the treatment of M. tuberculosis?
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1) Emergence of multiple-drug-resistant strains of M. tuberculosis.
2) Need for long therapy, which decreases compliance and selects for resistant strains. |
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What are five drugs used to treat M. tuberculosis infection?
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RIPE
1) Rifampin 2) Isoniazid (INH) and Vitamin B6 3) Pyrazinamide 4) Ethambutol |
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What is the time course for M. tuberculosis treatment?
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6-9 months, depending on the drug regimen and local resistance rates to the drugs used
Note: treatment time course is in constant flux. |
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How long does it take for an infected patient to be rendered noninfectious with treatment?
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2-3 weeks
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What drug regimen is used for active M. tuberculosis prophylaxis?
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INH for 6-9 months with supplemental vitamin B6
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Who gets prophylaxis for M. tuberculosis?
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1) Asymptomatic persons with a positive PPD
2) Children exposed to patients with active TB 3) Patients with a positive PPD who will become immunosuppressed (HIV patients). |
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What is one complication of INH prophylaxis?
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Hepatitis
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Who is at increased risk for this complication?
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1) Persons >35 year of age
2) Persons with a history of alcohol abuse. |
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Is there a vaccine for M. tuberculosis?
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YES
BCG vaccine |
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Is the vaccine for M. tuberculosis given in the US.
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NO
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What type of vaccine is M. turberculosis?
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Live-attenuated vaccine containing M. bovis.
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Should the TB vaccing be given to the immunocompromised?
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NO
It's a live vaccine |
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What do atypical mycobacteria cause?
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Tuberculosis, usually with disseminated rather than pulmonary manifestations
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What are four atypical mycobacteria?
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M. avium-intracellulare (MAC)
M. kansasii M. scrofulaceum M. bovis |
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Do M. avium-intracellulare (MAC)
M. kansasii M. scrofulaceum M. bovis cause a positive PPD? |
YES
but not always |
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Which atypical mycobacterial opportunistic infection classically affects AIDS patients?
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MAC
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What CD4 counts are usually associated with MAC infection in AIDS patients?
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CD4<50
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What is a common complication of MAC in the immunocompromised?
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Disseminated, or miliary disease.
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What diseaseis associated with MAC infection in teh non-AIDS population?
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COPD
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What disease is M. scrofulaceum associated with?
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Scrofula
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What physical finding is seen in Scrofula?
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Cervical lymphadenitis
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What patient population is scrofula commonly seen in?
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Children
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What is the etiology of scrofula?
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M. tuberculosis
M. scrofulaceum |
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What is the source of M. bovis?
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Unpasteurized milk
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What makes M. bovis useful?
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Attenuated strains of M. bovis are used to make a vaccine against tuberculosis.
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What are M. leprae?
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Obligate, intracellular, acid-fast bacilli indistinguishable from other mycobacteria.
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What is an animal reservoir for M. leprae?
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Armadillos
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What temperatures does M. leprae prefer?
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Cool temperatures (30C)
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What areas of the body does M. leprae infect?
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Superficial areas that are cooler
(skin, superficial nerves) |
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What are two clinical manifestations of M. leprae?
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Tuberculoid leprosy
Lepromatous leprosy |
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How is M. leprae transmitted?
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Prolonged contact with patients infected with lepromatous leprosy.
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What is the eponym for leprosy?
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Hansen disease
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What are the major differences between the two forms of leprosy?
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Tuberculoid leprosy:
1) Cell-mediated immune response 2) Granuloma formation 3) Containment Lepromatous leprosy: 1) Humoral response 2) NO granuloma formation 3) Dissemination |
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Clinically, what is the significance of the differences between the two forms of leprosy?
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Tuberculoid leprosy has few lesions and little tissue destruction.
Lepromatous leprosy has many lesions with extensive destruction of bone and overlying soft tissues, resulting in the typical "leonine facies" |
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Which form of leprosy has the worse prognosis?
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Lepromatous leprosy
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What is a feared complication of lepromatous leprosy?
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Erythema nodosum leprosum
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What is the treatment for erythema nodosum leprosum?
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Thalidomide
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In which form of leprosy is the lepromin skin test positive?
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Tuberculoid form
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Can M. leprae be grown in culure?
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NO
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How is M. leprae diagnosed?
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Acid-fast stain of infected tissue samples.
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What is the treatment for leprosy?
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Dapsone
Rifampin Clofazimine for approximately 2 years. |
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What are two complications of this prolonged coure of treatment for leprosy?
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Hemolysis
Methemoglobinemia |
