Surgical Microbiology & Immunology Flashcards

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

Answer: Staphylococcus aureus

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

Which type of hypersensitivity reaction is responsible for anaphylaxis?

Answer: Type I (IgE-mediated)

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

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

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

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

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

Answer: Clostridium perfringens

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

Which cells are the primary effector cells of innate immunity?

Answer: Neutrophils and macrophages

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

What is the precise definition of bacteraemia?

Answer: The presence of viable bacteria in the bloodstream

Bacteraemia is defined as the presence of viable bacteria in the bloodstream, which may be transient (e.g. following a dental procedure) or persistent.

Which sterilisation method is most appropriate for heat-sensitive surgical equipment such as fibreoptic endoscopes?

Answer: Ethylene oxide (ETO) gas sterilisation

Ethylene oxide gas achieves sterilisation at low temperatures (37–63°C) and is therefore suitable for heat-sensitive equipment that would be damaged by autoclaving.