Infectious Diseases part 3

Question 1

Microbial damage depends on what?

Answer 1

• The ability of the infecting bacteria to adhere to host cells, invade cells & tissues or deliver toxins.

Question 2

What are pathogenicity islands?

Answer 2

• Clusters of virulence genes in microbial genome.

Question 3

What is quorum sensing?

Give example

Answer 3

Coordinated virulence factors expression by autoinducer peptides. occurs in large bacterial populations.
- S.aureus

Question 4

What are Adhesins?

Answer 4

Adhesinsare bacterial surface proteins that bind bacteria to host cells or extra­cellular matrix.
- Pili for example.

Question 5

S. pyrogens (GAS) adhesins?

Answer 5

• Protein F and Teichoic acid, which binds to fibronectin on the surface of host cells and ECM.

Question 6

There is a specific E.coli strain that cause urinary tract infections. what special about this strain?

Answer 6

• This strain express unique P-pilus that binds to epithelial cells of the urinary tract.

Question 7

Endotoxin is

Answer 7

LPS that is a component of gram negative membrane.

Question 8

LPS composed of..

Answer 8

• Lipid A connected to a core sugar. attached to the core sugar there is “O antigen” which is used to serotype specific strains.

Question 9

How LPS works to establish inflammatory response?

Answer 9

Lipid A binds to CD14 and the complex then binds to TLR4.

Question 10

Exotoxins are secreted proteins that cause cellular injury. Classify them to broad categories:

Answer 10

• Enzymes - degrades host components
• A-B toxins (a-active, b-binding) - alter intracellular signaling and regulatory pathways.
• Superantigens causing massive response of T cells (Toxic Shock Syndrome)
• Neurotoxins
• Enterotoxins - affect the GI tract.

Question 11

What are the symptoms of the enterotoxins of the following microbes:

• S.aureus
• V. cholera
• C.difficile

Answer 11

• S.aureus -> vomiting and nausea
• V.cholera -> watery diarrhea
• C. difficile -> bloody diarrhea

Question 12

Host immune response sometimes can be the cause of tissue injury.
give example of T cells mediated inflammation which damage specific tissue type

Answer 12

• The damage to hepatocytes following HBV and HCV infection in mainly due to immune response to the infected liver cells and not to cytopathic effects of the virus.

Question 13

There are 5 major histological patterns of tissue reaction in infections. what are they?

Answer 13

• Purulent (Suppurative) Inflammation
• Mononuclear and Granulomatous Inflammation
• Cytopathic-Cytoproliferative
• Necrosis
• Chronic Inflammation/ Scaring

Question 14

Purulent (Suppurative) Inflammation characterized by:

Answer 14

• Exudate consisting of neutrophils, liquefied necrotic cells and edema.
• The neutrophils are attracted to the site of infection by release of chemoattractants from the “pyogenic” (pus-forming) bacteria that evoke this response, mostly extracellular gram-positive cocci and gram-negative rods. Masses of dying and dead neutrophils and liquefactive necrosis of the tissue form pus.

Question 15

Mononuclear Inflammation characterized by:

Answer 15

• Diffuse mononuclear interstitial infiltrates are common features of chronic inflammation.
• When they appear acutely is often due to viral infection, intracellular bacteria or parasites.

Question 16

Granulomatous inflammation is?

Answer 16

A distinctive form of mononuclear inflammation usually evoked by infectious agents that resist eradication and are capable of stimulating strong T cell–mediated immunity

Question 17

Cytopathic-Cytoproliferative

Answer 17

• Usually occurs by viruses.
• Necrotic cells / Cellular proliferation (HPV).
• Blisters (focal cell damage in the skin)
• Viral aggregates that are visible as inclusion bodies (e.g., CMV or adenovirus)
• Multinucleated cells called polykaryons (e.g., measles virus or herpesviruses).
• Can contribute to malignant neoplasia.

Question 18

Necrosis Tissues…

Answer 18

• Clostridium perfringensand other organisms such asC. diphtheriaecause such rapid and severe necrosis (gangrenous necrosis) by toxins secretion.
• The parasiteE. histolyticacauses colonic ulcers and liver abscesses characterized by extensive tissue destruction with liquefactive necrosis and little inflammatory infiltrate.
• Some viruses can cause widespread and severe necrosis of host cells associated with inflammation, as exemplified by total destruction of the temporal lobes of the brain by herpesvirus or the liver by HBV.