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28 Cards in this Set
- Front
- Back
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What are the two species of Mycobacterium?
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1. M. tuberculosis
2. M. leprae Humans are the only species infected with these critters. Their high lipid content makes them acid-fast. |
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Name 2 species that are acid fast.
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Mycobacterium/Nocardia
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What does acid fast mean?
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Example stain:
a smear of sputum is covered with the red stain, "carbolfuchsin" and heated to aid dye penetration. Acid alcohol(95% ethanol and 3% HCL) is poured over the smear, and a counterstain of methylene blue is applied. The cell wall lipids of the mycobacterium do not dissolve when the acid alcohol is applied, and the red stain does not wash off. Acid fast organisms resist decolorization with acid alcohol, holding fast to their red stain. |
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The acid fast bacillus rod is an obligate aerobe(lungs). TRUE/FALSE
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TRUE. Infact, it grows very slowly taking up to 6 weeks for visible growth.
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Mycosides is one class of lipid that only acid fast organisms have and that is involved in mycobacterial virulence. TRUE/FALSE
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TRUE.
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What is Mycolic acid?
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It is a large fatty acid.
Mycoside is a mycolic acid bound to a carbohydrate, forming a glycolipid. |
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What is Cord factor?
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It is a mycoside formed by the union of 2 mycolic acids with a disaccharide(trehalose). This is only found in virulent strains of M. tuburculosis(bacterial growth appears as cords.
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Why is Cord factor virulent?
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Cord factor inhibits neutrophil migration and damages mitochondria. Infact, its injection into mice results in the release of TNF or cachectin, resulting in rapid weight loss.
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What are sulfatides?
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They are mycosides that resemble cord factor with sulfates attached to the disaccharide. They inhibit the phagosome from fusing with the lysosome that contains bacterial enzymes.
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What is Wax D?
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It is a complicated mycoside that acts as an adjutant(enhances antibody formation to an antigen) and may be part of M. tuburculosis that activates the protective cellular immune system.
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Regarding pathogenesis, what is facultative intracellular growth?
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With first exposure(lungs), the host has no specific immunity. Bacteria cause a local infiltration of neutrophils and macrophages. Phagocytosed bacteria are not destroyed. The bacteria cruise through the lymphatics and blood to set up camp in distant sites.
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What is Mycobacterial cell mediated immunity?
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Some macrophages succeed in phagocytosing and breaking up the invading bacteria. these macrophages will present parts of the bacteria to T helper cells. T cells will release lymphokines to attract other macrophages.
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What causes caseous necrosis?
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Macrophage attack results in local destruction and necrosis of lung tissue. The soft caseous center is surrounded by macrophages and giant cells and fibroblasts with collagen. These deposits frequently calcify.
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What is the PPD test?
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Following induction cell mediated immunity against M. tuburc., any additional exposure to this organism will result in a localized delayed type sensitivity reaction(type 1V).
Intradermal injection of antigenic protein particles from killed M. tuburc. called PPD(Purified protein derivative) results in localized skin swelling and redness. PPd should reveal whether a person has been exposed to M. tuburc. |
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What causes the skin reaction?
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Macrophages in the skin will take up the antigen and deliver it to the T cells. The T cells move to the skin site, release lymphokines, that activate macrophages and within 1-2 days the skin will become red raised and hard. A positive test is considered when area of induration is bigger than 10mm after 48hrs(5mm in AIDS patients)
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Do false positive M. tuburculosis tests exist?
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Yes. Some people from other countries have had the BCG(bacillus Calmette -Guerin vaccine. Though it may prevent tbc, it usually causes a positive PPD.
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Do false negative tests exist?
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Yes. Some people do not react to the PPD even if they have been infected with tbc.These patients are usually anergic, which means that they lack a normal immune response due to steroid use, malnutrition, AIDS etc.
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What is primary tbc?
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It is usually a subclinical lung infection. In an asymptomatic primary infection the acquired cell mediated immunity will wall off and suppress the bacteria. These bacteria lie dormant, but can be reactivated at a later date. Close contacts have a 30% chance of being infected.
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M. tbc. is usually transmitted via aerosolized droplet nuclei from the aerosolized respiratory secretions. TRUE/FALSE
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TRUE.
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What is asymptomatic primary infection?
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The cell mediated defenses kick in, and the foci of bacteria become walled off in the caseous granulomas.
A calcified turburcle in the middle or lower lung zone is called a GHON focus. When it is accompanied by perihilar lymphnode calcified granulomas, it is referred to as a Ghon, or Ranke complex. |
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Most adult cases of tbc occur after the bacteria have been dormant for some time. This is reactivation tbc, and may be a result of a weakened immune system. TRUE/FALSE
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TRUE.
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What other organ systems can tbc affect?
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Pulmonary
Pleural Lymph node- most common. This condition is called Scrofula. Kidney Skeletal Joints CNS Miliary tbc-Millet sized tuburcules are disseminated all over the body. Occurs in the elderly and children. |
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What is Mycobacterium avium intracellulare(MAI)?
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This organism only infects birds avium and other animals. It has now become one of the major systemic bacterial infections of AIDS patients. Infact, 50% of AIDS patients examined at autopsy are found to be infected with MAI. It causes a chronic wasting illness.
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What is Mycobacterium leprae?
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It is an acid fast rod. It cannot be grown on artificial media. It has been grown in the footpads of mice, in armadillos and in monkeys. It causes leprosy. The bacteria appear to grow better in cooler body temperatures closer to the skin surface.
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Clinically, leprosy is broken up into 5 subdivisions based on the level of cell mediated immunity. What are they?
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1. Lepromatous leprosy(LL)
2. Tuburculoid leprosy(TL) 3. Borderline lepromatous(BL) 4. Borderline(BB) 5. Borderline tuburculoid(BT) |
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What is Lepromatous leprosy?
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This is the severest form of leprosy, because patients cannot mount a cell mediated immune response. Defective T suppressor cells(T-8) cells block thr T helper cells response to the mycobacterium leprae antigens.
Skin lesions cover the body with lumps. facial skin is very thickened(leonine facies) |
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What is Tuburculoid leprosy?
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Patients with TL can mount a cell mediated defense against the bacteria, thus containing the skin damage so it is not excessive. This is a milder and occasionally a self limiting disease.
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What is the Lepromin skin test?
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This test is similar to the PPD used in tbc. IT measures the ability of the host to mount a delayed hypersensitivity reaction against antigens of Mycobacterium leprae.
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