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39 Cards in this Set

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  • Back
What two bacteria that are important in the acid-fast category?
Mycobacterium tuberculosis and leprae
Mycobacterium are what kind of bacteria?
Obligate aerobe, that are thin rods with lipid-laden cell walls, making them acid-fast on staining.

They are also facultative intracellular that seek refuge in macrophages.
Since acid fast bacillus is an obligate aerobe, where does it commonly infect?
The lungs, where oxygen is abundant--in the upper lobes.
What is the one class of lipids involved in mycobacterial virulence?
Mycosides, a mycolic acid (large fatty acid) bound to a carbohydrate, forming a glycolipid.
What is cord factor, where is it found, and what does it result in?
It is a mycoside formed by the union of 2 mycolic acids with a disaccharide. It is only the virulent strains of Mycobacterium tuberculosis. It results in parallel growth of the bacteria, making them appear as cords.
Cord factor may cause what?
Inhibits neutrophil migration and damages mitochondria. Injection into mice, results in the release of TNF (or cachectin), resulting in rapid weight loss (which occurs with TB).

It also stimulates formation of granulomas.
What are sulfatides?
Mycosides resembling cord factors with sulfates attached to the disaccharide. They inhibit phagosome from fusing with the lysosome that contains bactericidal enzymes.
What is wax D?
A mycoside that acts as an adjuvant (enhances AB formation to an antigen) and may activate the protective cellular immune system.
When M. TB enters, what occurs?
The host has no specific immunity initially. TB survives in the neutrophils and macrophages due to virulence factors. The host the acquires its prime defense against the TB, cell-mediated immunity. Some of the macrophage succeed in breaking up the bacteria, and they then can present the antigens on their cell surface in the lymph node to helper T-cells. When T-cells then secrete lymphokines upon encountering their antigenic target; therefore, macrophages are activated and can now destroy the bacteria.
When the macrophages are activated against TB, what results?
Caseous necrosis results. This is when the macrophage attack and cause necrosis of lung tissue. This soft caseous center is surrounded by macrophages, multi-nucleated giant cells, fibroblasts, and collagen deposits and frequently calcifies. This granuloma keeps the bacteria at bay but it remains viable.
What type of hypersensitivity is the PPD (Purified Protein Derivative) test?
Type IV
A person with a positive PPD test, is considered to have?
Latent tuberculosis
What can give a false positive test for PPD?
BCG (Bacillus Calmette-Guerin) vaccine for TB. This vaccine is debatably effective in preventing TB, but may result in positive PPD.
What can give a false-negative test?
PTs who are usually anergic, which means that they lack a normal immune response due to steroid use, malnutrition, AIDS, etc.
What is primary TB?
The bacteria is transmitted from aerosolized droplet nuclei form infected individuals. It lands in the area of greatest air flow in the lungs: middle and lower lobes. The bacteria then enters macrophages, multiply and spread to regional lymph nodes.
Cell-mediated immunity can result in asymptomatic primary infection or systematic primary infection. Explain both.
With asymptomatic infection, the bacteria is walled off in caseous granulomas, which heal with fibrosis, calcification, and scar formation. The bacteria decrease in numbers, but remain viable.

Symptomatic occurs less frequently, but in children, elderly, and immunocompromised individuals. Organisms are not suppressed.
A calcified tubercle is called?
A Ghon focus.
A Ghon focus accompanied by perihilar lymph node calcified granulomas is called?
A Ghon or Ranke, complex.
What is secondary or reactivation TB?
Most adult cases of TB occurs as latent TB after the bacteria have been dormant for some time. It is presumed that a temporary weakening of the immune system may precipitate reactivation.

Sometime after reactivation, the material within the granulomas becomes caseous. The central area of the granulomas undergoes necrosis, and may break into a bronchus discharging M. tuberculosis into exhaled air.
What organs are involved in TB?
Lung, pleural and pericardial infection; lymph nodes (mainly cervical; kidney (sterile pyuria); skeletal (chronic arthritis of 1 joint typically); CNS (subacute meningitis and granulomas in the brain); and miliary tuberculosis.
What is scrofula?
Lymph node tuberculosis: swollen, matted together, and drain.
What is sterile pyuria?
PTs will have RBC and WBC in urine, but no TB will be seen on Gram stain or grow in culture (M. TB takes weeks to grow).
What is Pott's disease?
Disseminated TB that invades skeletal tissues, resulting in IV discs and adjacent vertebral bodies being destroyed, causing osteomyelitis.
What is miliary tuberculosis?
Tiny millet-seed-sized granulomas (tubercles) disseminated all over the body like a shotgun blast: kidneys, lungs, liver, and other organs.
How do you diagnosis TB?
PPD skin test, chest x-ray, and sputum acid-fast stain and culture.

Culture: Lowenstein-Jensen agar

+ PPD: >15 mm; with AIDS >5 mm.
How do you treat Mycobacterium tuberculosis?
Treat with RIPES (multiple drugs to avoid resistance): rifampin, isoniazid (INH), pyrazinamide, ethambutol, streptomycin.

Prophylaxis (for PPD +), INH
What is a major pathogen of AIDS PTs, resistant to multiple drugs, results in chronic wasting illness, bacteria dissemination, and chronic watery diarrhea?
Mycobacterium avium-intracellulare
What causes leprosy?
Mycobacterium leprae
Can M. leprae grow on artificial media?
No, only on footpads of mice, armadillos, and in monkeys.
Who can catch leprosy?
Only those who are susceptible, with exposed skin lesions from an infected individual or respiratory secretions (more likely).
What is dependent for leprosy to result in an infection?
1) The bacteria grows better in cooler body temperatures closer to the skin surface; 2) Severity of disease is dependent on host's cell-mediate immune response to the bacilli.
What does leprosy affect?
Damages skin (sparing warmer areas, such as the armpit, groin, and perineum) and superficial nerves, eyes, nose, and testes.
What is the severest form of leprosy, because the PT cannot mount a cell-mediated immune response.
Lepromatous leprosy
What occurs with Lepromatous leprosy?
Leonine facies (facial skin becomes thinkened, like a lion); saddlenose deformity (nasal cartilage destroyed); internal testicular damage (infertility); anterior segment of eyes damaged (blindness); peripheral nerves are thickened (loss of sensation in glove and stocking distribution); inability to feel fingers and toes (leading to trauma and secondary infections); contraction and resorption of fingers and toes.
What is tuberculoid leprosy?
PTs can mount an immune response, so skin damage is not excessive, and sometimes results in a self-limiting disease.

Localized superficial, unilateral skin and nerve involvement. 1 - 2 skin lesions. Well-defined, elevated blotches. Enlarged nerves can be palpated that are close to the skin (greater auricular, ulnar, posterior tibial, and peroneal)
Who would have a true positive result from a lepromin skin test, and who would have a false negative, and why?
PTs with tuberculoid leprosy would have a true positive since they have a cell-mediated immune response. PTs with lepromatous leprosy would have a false negative, since they cannot mount a cell-mediated immune response.
How do you treat leprosy?
Dapsone, rifampin, clofazamine. Used in combination to prevent resistance.
What contributes to enhance virulence of Mycobacterium tuberculosis?
LAM, which is recognized by macrophage mannose receptor.
What is a tubercle?
Fibrotic, calcified scars, OR:

Chronic granuloma encapsulated with fibrin. It has a central area of large, multinucleated giant cells containing tubercle bacilli, midzone of epithelioid cells, and a peripheral zone of fibroblasts, lymphocytes, and monocytes.