Professional Pathogens

Question 1

What are the 5 mechanisms of virulence for Staph Aureus? (5)

Answer 1

1. Surface proteins in cell wall - adhesins (tissue adherence, colonisation and deep infection)
2. Secreted Proteins based on phase
3. Capsule
4. Coagulase Enzyme
5. Quarum-Sensing Accessory Gene regulator to control gene expression.

Question 2

What are the cell wall adhesins in Staph Aureus? (4)

Answer 2

1. Fibronectin binding protein
2. Collagen binding protein
3. Elastin Binding protein
4. Protein A - this has immunoglobins wrong way around to help immune evasion.

Question 3

What are the main secreted proteins (exotoxins) in S. Aureus? (3)

Answer 3

1. Cytotoxins - Form pores to lyse host cell
2. Exfoliative toxins - proteases which target epidermal structural proteins
3. Enterotoxins (superantigens) - stimulate massive T cell activation

Question 4

What is the role of Coagulase in S. Aureus? (2)

Answer 4

Stimulates clotting and helps immune evasion.

Used as test to distinguish S. Aureus from other staphylococci

Question 5

What is role of the thin polysaccharide capsule in S. Aureus? (2)

Answer 5

Masks cell surface features from immune system to avoid phagocytosis by neutrophils.

Question 6

What are examples of S. Aureus Infections? (3)

Answer 6

1. Skin infections: Impetigo; Staphylococcal abscess; Furunculosis
2. Sepsis: In patients with with vascular treatment line (e.g heart valves, cancer treatment, bone and joints etc) can cause sepsis as can seep into blood.
3. Food poisoning: If enterotoxins are ingested can cause vomiting and some diarrheoa.

Question 7

Why is innate immune system very sensitive to Lipopolysaccharide and what is response? (4)

Answer 7

1. Lipopolysaccharide interacts with “Toll-like receptors” on Monocyte/macrophage lineage cells and the vascular endothelium.
2. Results in Systematic activation of:
   * Inflammatory pathways
   * Coagulation and clotting pathways
   * Makes blood vessels leaky
   Clinically manifests as Sepsis

Question 8

Where in the body are adhesins in Gram-Negative Neissera Meningitidis (Meningococcal) specially adpated to? (2)

Answer 8

1. Respiratory Epithelium

2. Meninges - Around Brain and Spinal cord

Question 9

Where in the body are adhesins in Gram-positive Streptococcus Pneumoniae specially adpated to? What can it cause? (3)

Answer 9

1. Respiratory Mucosa. It binds to cell membrane cholesterol.

Can cause:

1. Upper resp infections.
2. It can cause heart valve infections and meningitis if gets into blood and travels.

Question 10

What is the mechanism of virulence for streptococcus Pneumoniae? (3)

Answer 10

1. Pneumolysin - Uses Forms pores and lyses ciliated and phagocytic cells.
2. Secretes Protease which breaks down secreted immunoglobin A, preventing mucosal clearance.
3. Other General Bacterial virulence mechanisms (like S. Aureus)