MCQs: Staphylococcus aureus: Answers

1) Most people are colonised with Staphylococcus aureus? T/F

False, most people colonised with coagulase negative staphylococci. Colonisation rate for Staphylococcus aureus probably 10-20% of the population.

2) The nuc gene is found in Methicillin Resistant Staphylococcus aureus? T/F

True: The nuc gene found in all Staphylococcus aureus but is not the resistant determinant for MRSA, which is MecA, coding for the PBP2A protein.

3) Methicillin is a commonly used antibiotic in many parts of the world? T/F

False: Essentially historical antibiotic, superseded by flucloxacillin, cloxacillin and dicloxacillin

4) Staphylococcus aureus can ferment mannitol? T/F

True: This creates acid by-product and turns phenol indicator in Mannitol Salt Agar to yellow, giving yellow colonies.

5) Coagulase is not thought to be an important virulence factor for Staphylococcus aureus? T/F

True: However useful for discriminating between Staphylococcus aureus and “coagulase negative staphylococci”

6) Staphylococcus aureus bacteraemia has a 30 day mortality of 15-20%? T/F

True: One of the hishest mortality rates for any bacterial species.

7) Staphylococcus aureus can cause food poisoning? T/F

True: Through the production of enterotoxins, usually with a short incubation period and short duration of symptoms.

8) Staphylococcus aureus is a motile organism? T/F

False: As far as I am aware, it is non-motile.

9) Staphylococcus aureus can be intracellular in nasal epithelial cells? T/F

True: Explaining why Staphylococcus aureus colonisation can be difficult to eradicate, and the lack of decolonisation activity of antimicrobials with little intracellular activity, such as flucloxacillin.

10) Staphylococcus aureus is a common contaminant in blood cultures? T/F

False: Most of the time when found in blood cultures, is pathogenic. Occasionally a contaminant. If only cultured from one bottle after a significant time period (ie >15hrs), this can be a pointer towards it being a contaminant.



6 thoughts on “MCQs: Staphylococcus aureus: Answers

  1. Actualy coagulase is important because it ables S. aureus to produce fibrin and create a “clot” that allows proliferation and prevents antibiotics from reaching the bacteria

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