C. acnes Spinal Implant Infection — SCE Infectious Diseases MCQ

Correct answer: C — IV Benzylpenicillin (or Amoxicillin) for 2–6 weeks IV then oral Amoxicillin for a total of 3–6 months

Cutibacterium acnes isolated from intraoperative deep samples in a patient with a deep surgical site infection after spinal fusion should be treated as a true low-virulence, biofilm-associated implant pathogen, not dismissed as contamination. Because the isolate is highly susceptible to benzylpenicillin, the preferred targeted regimen is a penicillin-class beta-lactam: IV benzylpenicillin or IV amoxicillin initially, usually after debridement/source control, followed by oral amoxicillin to complete a prolonged implant-associated course. A total duration of 3–6 months is used when spinal metalwork is involved or retained, with the IV phase typically 2–6 weeks before oral step-down if clinically improving. Vancomycin or daptomycin are alternatives mainly for beta-lactam allergy/resistance and are unnecessarily broad here; 2 weeks alone is inadequate for deep implant-associated infection. Metronidazole is not appropriate therapy for C. acnes.

Reference: NHS Lothian Right Decisions. Guidelines for the use of antibiotics in adult trauma and orthopaedic surgery, Version 18, review date September 2024: Cutibacterium spp treated with IV benzylpenicillin followed by oral amoxicillin, with prolonged therapy for implant-associated infection. https://rightdecisions.scot.nhs.uk/media/2345/orthopaedic-surgery.pdf