Periprosthetic knee joint infection caused by Sneathia sanguinegens

Sneathia sanguinegens is a fastidious, Gram-negative, rod-shape organism rarely isolated from human specimens. In the present report, we describe a case of periprosthetic knee joint infection due to the organism, which occurred in a female patient receiving immunosuppressants for underlying lupus nephritis. The causative organism was isolated from the synovial fluid in the affected knee joint through inoculating the material on chocolate agar and incubation for 15 days under 5% CO₂. Moreover, the organism was capable to be subcultured on chocolate agar with incubation for a few days under 5% CO₂, demonstrating that this uncommon organism, although generally considered as a strict anaerobe, is culturable in aerobic condition if appropriate media and a sufficient incubation time are given. The patient was treated with intravenous cefepime, an antibiotic highly active to the isolated organism in an in vitro study, in addition to intraarticular debridement and exchanging a polyethylene insert in the affected joint. The antimicrobial therapy with cefepime was given for 19 days and, thereafter, changed with oral levofloxacin. Although the patient showed full recovery after administration of levofloxacin for 100 days, an in vitro study conducted later revealed that levofloxacin was inactive to the isolated organism.