CRRAB Microbiology - HIV and Tb Flashcards Preview

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Flashcards in CRRAB Microbiology - HIV and Tb Deck (16)
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1
Q

What important properties distinguish Mycobacterium from other genera of gram-positive rods?

A

Lipid-rich cell wall responsible for important distinctions:

  • acid fast
  • slow growth
  • resistance to detergents
  • resistance to common anitbacterials
2
Q

Why is one third of the world population infected with M. tuberculosis?

A

M.Tb can establish chronic infections that persist for life. As immunity wanes in old age or disease the organism can activate and produce disease. Highly infectious, so spreads person to person quickly.

3
Q

What populations are at risk for infection with M. avium or M. fortuitum?

A

M. Avium infects immunosuppressed and those with chronic pulmonary disease (like bronchiectasis)

M. Fortuitum is introduced into wounds or IV catheters

4
Q

What is unique about the cell wall of mycobacteria, and what biologic effects can be attributed to the cell wall structure?

A

Cell wall is unique in that it has long chain mycolic acids.
The unique lipid-rich cell wall renders the organisms acid-fast and resistant to detergents, common antibacterial antibiotics, and many disinfection procedures.

5
Q

Why is M. tuberculosis more virulent in patients with HIV infection than in non–HIV-infected patients?

A

Normally, mycobacterium replication triggers CD4 helper and CD8 cytotocic T-cells. T cells then release IFN-gamma and other cytokines to activate macrophages that can destroy the mycobacterium.
HIV positive patients have depressed CD4 cells, which allows mycobacterium to go crazy.

6
Q

What are the two clinical presentations of M. leprae infections? How do the diagnostic tests differ for these two presentations?

A

Clinical spectrum ranges from mild tuberculoid leprosy to severe lepromatous leprosy.

Tuberculoid

  • hypopigmented skin macules
  • few bacilli in the tissue
  • strong cellular immune reaction (positive skin test)

Lepromatous

  • disfiguring skin lesions, nodules, plaques, thick dermis
  • abundance of bacilli in infected tissue
  • strong antibody response, but weak cellular immunity
7
Q

Why do mycobacterial infections have to be treated with multiple drugs for 6 months or more?

A

They replicate slowly. Prolonged therapy is required to eliminate them completely. 1 per 100,000 or million bacteria develop resistance. So if there are a ton of bacteria, it’s easy to see how resistant bacteria could be selected for.

8
Q

What cell types does HIV infect, and why does this have such an impact on the patient’s immune response?

A

HIV cells infect CD4 cells on the CCR5 or CXCR4 chemokine receptors.
Includes CD4 Tcells, macrophages, and dendritic cells

9
Q

How does the HIV virus replicate?

A
Virus binds to chemokine receptor, fuses envelope with cell membrane, and delivers the virion and genome into the cytoplasm.
Next the (+)RNA is reverse transcribed into DNA and integrated into the host DNA.
mRNA is transcribed including full-length (+)RNA which becomes the new viral genome and viral protease cleaves virion proteins into individuals proteins in the viral envelope.
10
Q

To what other opportunistic infections is this woman susceptible?

A

Other intracellular bacteria (M. Avium, Salmonella), viruses (herpes), fungal infections, and malignancies (lymphoma, kaposi sarcoma)

11
Q

What are risk factors for HIV infection?

A

Unprotected sex, exposure to blood, IV drug use.

12
Q

How do you treat HIV?

A

HAART combines multiple antiretroviral drugs to limit the potential selection of resistant mutants.
The drugs target the reverse transcriptase, integrase, protease, CCR5 co-receptor, or block the fusion event.

13
Q

Lab tests to support and confirm HIV diagnosis?

A

Dx: Presence of HIV and CD4 count under 200/microL

HIV presence:
-antibodies to HIV by ELISA/Western
OR
-HIV genome by RT-PCR

CD4 Count:
-flow cytometry

14
Q

Immunological basis for increased susceptibility to opportunistic infection with HIV?

A

Reduced CD4 cells, reduces body’s ability to make interferon-gamma to activate macrophages and other protection

15
Q

What precautions should be taken in handling samples from this patient?

A

Universal blood precautions,

Gloves, protective eyewear, clothes

16
Q

Several forms of HIV vaccines are being developed. What are possible components of an HIV vaccine? Who would be appropriate recipients of an HIV vaccine?

A

Important viral component is gp120 glycoprotein. The viral attachment protein - antobodies to this protein neutralize the virus.
Maybe Gag a possibility too
Persons who would benefit most from vaccine:
healthcare workers, promiscuous homosexuals/heterosexuals, drug addicts