A 42-year-old man with subacute endocarditis has three blood culture sets negative after the standard 5-day incubation protocol. Echocardiography shows a mitral vegetation. Which organism pair should the laboratory specifically suspect, requiring extended incubation up to 21 days or special conditions?
- A HACEK group organisms and Brucella species ✓
- B Viridans streptococci and Enterococcus faecalis
- C Staphylococcus aureus and coagulase-negative staphylococci
- D Streptococcus bovis and Abiotrophia defectiva
Correct answer: A. HACEK group organisms and Brucella species
Explanation
HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella) are fastidious gram-negative bacilli needing CO2 and up to 21 days of incubation, and Brucella may require prolonged culture or specific media. Viridans streptococci, enterococci and staphylococci grow within the routine 5-day window, so they cannot explain culture negativity under standard protocols.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.