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36 Cards in this Set

  • Front
  • Back
What characterizes Mycobacterium tuberculosis?
- Long, slender, straight or curved
- Acid fast bacilli
- Slow grower
- Obligate aerobes
- Intracellular bacterium
What is unique about the cell wall of Mycobacterium?
It is composed of high molecular weight acidic waxes; mycolic acid, Wax D, cord factor, and sulfatides.
What is the purpose of the complex cell wall of Mycobacterium?
- Resists phagocytosis, disinfectants, dessication, and antibiotics.
What are the virulence factors associated with Mycobacterium tuberculosis?
- Complex Cell Wall
- Intracellular (hidden from humoral response)
- Siderophores - iron acquisition
- Antibiotic Resistance (via chromosomal mutations and genges
- Inhibits phagolysosome formation
What proteins are responsible for inhibition of phagosome-lysosome fusion in macrophages?
ESAT-6 and CFP-10 (Both are found encoded RD1 region of the chromosome).
How does transmission of TB occur?
Inhalation of respiratory mucus droplets in the air (inoculum size is high, repeated exposures are typically required except in susceptible individuals).
What is the pathogenesis of primary course of TB?
Inhalation of bacteria --> bacteria are small enough to proceed to the alveoli where they invade alveolar macrophages ---> migrate to the lymph nodes where they initiate immune response --> in the lungs, lesions form and granulomas develop --> activate macrophages fight the infection --> bacteria stop growing, and calcification of the lesion occurs.
What is meant by a secondary TB infection?
Reactivation of bacteria already present in the host (more common) or re-infection with M. tuberculosis (in endemic areas; less common).
What characterizes the tubercles seen in TB?
They are granulomas with a central core of M. tuberculosis surrounded by macrophages and T-cells (bacilli cause caseous necrosis); the granulomas can calcify at which point they are known as Ghon complex.
What describes the immune response regarding TB?
CD4+ T-cell response --> they secrete INF-gamma and TNF which activate macrophages --> macrophages secrete inflammatory cytokines (TNF, IL-1, IL-6, IL-8, and GM-CSF) which cause inflammation and granuloma formation.
What signs/symptoms are associated with active TB infection?
- Fever
- Night Sweats
- Weight Loss
- Cough
- Hemoptysis
- < appetite
- Abnormal CXR
What damage is seen in disseminated tubercuolosis (miliary and extrapulmonary)?
- Renal Necrosis and scarring
- Degeneration of spine (Potts' Disease)
- Damage to reproductive organs
- Meningitis
What stain is used for the direct identification of acid-fast bacilli from bronchoalveolar lavage (BAL) or sputum?
Ziehl-Neelsen Stain (Acid Fast) or Fluorescent Dye
What method of detection is now used for the cultivation of Mycobacterium tuberculosis in the laboratory?
Fluorometric Dectection (4-8 days), isolation of bacteria (3-6 days), drug susceptibility (2-3 days) - total time 10-14 days.
What is the old method of cultivation of Mycobacterium tuberculosis in the laboratory?
Lowenstein-Jensen Media (4-8 weeks)
How is the diagnosis of latent TB made?
Tuberculin Skin Testing (PPD) - measure the induration, not the erythema. A positive PPD means there is a current or prior infection.
For which group of individuals is a 5 mm induration with a PPD interpreted as positive for TB?
- HIV patients
- Close contact to case of infectious TB
- Patient with abnormal CXR
- Immunosuppressed
- Organ transplant recipients
For which group of individuals is a 10 mm induration with a PPD interpreted as positive for TB?
- Person with clinical conditions that place them at high risk.
- Children < 4 yrs of age
- Adolescents exposed to adults at high risk
For which group of individuals is a 15 mm induration with a PPD interpreted as positive for TB?
- Individuals with no known risk factors for TB.
What type of reaction is the response to a PPD?
Type IV, delayed-type hypersensitivity
How does QuantiFERON (TB Gold) work?
In vitro assay that uses whole blood from a patient to measure cell-mediated immune response to ESAT-6 and CFP-10 antigens by looking for IFN-gamma production through ELISA. If you possess antigen specific T-cells they will respond to ESAT-6 and CFP-10 producing IFN-gamma.
What are the advantages of using QuantiFERON (TB Gold)?
- Single Patient visit
- Only response to M. tuberculosis
- No "booster phenomena"
- Eliminates subjectivity
- Safe, uses whole blood and results w/in 24 hrs
What is the treatment for active TB infection?
Four Drug Treatment Until known susceptibilities:
- Isoniazid
- Rifampin
- Pyrazinamide
- Ethambutol
Length of Treatment 6-24 months
What is the meaning of the mnemonic DOTS?
Directly Observed Treatment, Short-Course - means that a health care worker directly observe the patient take their anti-TB drugs.
What characterizes M. avium complex (MAC)?
- Major cause of death in AIDS patients
- Can colonize the GI and respiratory tract and then disseminate
- Very drug resistent
What characterizes M. kansasii?
- Causes pulmonary infection
- Non-communicable
- Treat with Isoniazid and Rifampin
What characterizes M. marinum?
- "Swimming pool granuloma," ulcer
- Non-communicable
- Treat with Rifampin and Ethambutol
What type of mycobacteria is considered to be a rapidly growing mycobacteria?
Mycobacterium fortuitum
What characterizes the Runyon Group IV mycobacteria?
Rapidly growing mycobacteria such as M. fortuitum; they are ubiquitous in the environment and opportunistic pathogens (skin lesions, abscesses) - can be a problem following plastic surgery.
What bacteria is the causative agent of leprosy (Hansen's Disease)?
Mycobacterium leprae - intracellular bacterium that grows in macrophages and Schwann Cells (long incubation period).
What is the transmission associated with M. leprae?
Transmitted via aerosolized droplets
What are the two major forms of leprosy?
- Tuberculoid
- Lepromatous
Describe the Tuberculoid form of M. leprae?
- Less Severe
- Cell-mediated Immunity (TH1)
Describe the Lepromatous form of M. leprae?
- More Severe
- Poor cell-mediated immunity (TH2)
- Damage to sensory nerve; loss of feeling leads to injury and secondary infections.
What is the treatment for the Tuberculoid form of M. leprae?
- Rifampin
- Dapsone
What is the treatment for the lepromatous form of M. leprae?
- Dapsone
- Rifampin
- Clofazimine