skip to main content

C. acnes Extended Blood Culture — SCE Infectious Diseases MCQ

Instant feedback + full explanation. One question, done properly.

ModerateBone & Joint InfectionC. acnes Extended Blood CultureSCE Infectious Diseases

A 55-year-old man with a prosthetic aortic valve develops endocarditis with Propionibacterium (Cutibacterium) acnes. Blood cultures took 12 days to become positive. This organism is slow-growing. What is the key laboratory requirement for detecting C. acnes endocarditis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Extended blood culture incubation (≥14 days) — standard 5-day culture protocols will miss C. acnes; the lab must be informed of suspected endocarditis to extend incubation

C. acnes is a slow-growing anaerobic Gram-positive rod that requires prolonged incubation (typically 7–14 days, sometimes longer) for isolation from blood cultures. Standard automated blood culture systems with 5-day incubation protocols will frequently miss C. acnes. When endocarditis is suspected clinically (especially prosthetic valve with culture-negative endocarditis), the microbiology laboratory must be informed to extend blood culture incubation to ≥14 days. C. acnes endocarditis predominantly affects prosthetic valves and can cause indolent but destructive disease.

Reference: ESC 2023 – Endocarditis; BSAC 2012 – Culture-negative endocarditis