FRCS Surgical Microbiology & Immunology 1

Question 1

Which organism is the most common cause of surgical site infections?

Accepted Answer

Staphylococcus aureus

Answer

Staphylococcus aureus, including MRSA, is the most frequent causative organism in surgical site infections due to its prevalence on skin and in nasal carriage.

Question 2

Which type of hypersensitivity reaction is responsible for anaphylaxis?

Accepted Answer

Type I (IgE-mediated)

Answer

Anaphylaxis is a Type I (immediate) hypersensitivity reaction mediated by IgE antibodies bound to mast cells and basophils, triggering rapid degranulation.

Question 3

What is the mechanism of action of beta-lactam antibiotics?

Accepted Answer

Inhibition of bacterial cell wall synthesis by binding penicillin-binding proteins

Answer

Beta-lactam antibiotics inhibit cell wall synthesis by covalently binding to penicillin-binding proteins (PBPs), preventing cross-linking of peptidoglycan chains.

Question 4

Which Clostridium species is the primary causative organism of gas gangrene (clostridial myonecrosis)?

Accepted Answer

Clostridium perfringens

Answer

Clostridium perfringens produces alpha-toxin (phospholipase C), which destroys cell membranes and is the primary virulence factor in gas gangrene.

Question 5

Which cells are the primary effector cells of innate immunity?

Accepted Answer

Neutrophils and macrophages

Answer

Neutrophils and macrophages are the principal effector cells of innate immunity, providing immediate non-specific defence through phagocytosis and release of inflammatory mediators.

FRCS Part A Practice Test

FRCS Part A Practice Test

FRCS Surgical Microbiology & Immunology 1