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Gram Stain VAP Organism Identification — FRCA Final MCQ

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EasyIntensive Care MedicineGram Stain VAP Organism IdentificationFRCA Final

A 55-year-old man (ASA III) in ICU develops ventilator-associated pneumonia. Gram stain shows gram-positive cocci in clusters. The most likely organism is:

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Correct answer: B — Staphylococcus aureus

Gram-positive cocci in clusters on Gram stain of respiratory specimens are characteristic of Staphylococcus species, most commonly S. aureus. In the ICU setting, both methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus are common causes of VAP. Empirical antibiotic choice depends on local MRSA prevalence: if MRSA risk is low (no prior colonisation, short ICU stay), flucloxacillin is appropriate; if MRSA risk is high, vancomycin or linezolid is added. Streptococcus pneumoniae forms chains or pairs (diplococci), not clusters.

Reference: NICE – 2022 – NG139 Hospital-acquired pneumonia; ICS – 2023 – VAP management