In October 2009, a 55-year-old male with diabetes mellitus, probably since 2007, peripheral artery occlusive disease (PAOD) without any notion of peripheral neuropathy, and a history of alcoholism in 2003 presented with right lower leg pain accompanied by local hyperthermia, swelling, and reddening without fever. The medical history revealed that, in August 2000, the patient had suffered from a grade III open comminuted tibia fracture associated with a compartment syndrome. The fracture had been fixed using intramedullary nailing and fasciotomy at the lower leg had been performed. An intraoperative swab had yielded aerobic spore-forming bacteria after enrichment culture without further differentiation, but no anaerobic bacteria. In August 2001, the patient presented with a pus-filled fistula at the distal third of the lower leg. At this time point, the intramedullary nail was removed and the tibia was reamed for the treatment of osteomyelitis. Staphylococcus aureus (S. aureus) was grown from intraoperative specimens with resistance to penicillin and ampicillin only. Intravenous cefuroxime was given for 34 days. After removal of the implant, including reaming of the long bone and aggressive debridement, the fistula at the lower leg healed slowly. In the following 8 years, no event of trauma, manipulation, or surgery to the right lower leg was recorded. Upon readmission, plain radiographs of the right lower leg showed the radiological sequelae of comminuted lower leg fracture with full consolidation of the fracture lines. Typical signal alterations were found at magnetic resonance imaging (MRI) scanning within the medullary canal, including enhancement after the application of contrast agent, suggesting osteomyelitis within the distal third of the tibia. The tibia was opened proximally and a phlegmon of the medullary cavity was drained. Aggressive wound debridement, including reaming and jet lavage, was done. A rod was formed from polymethylmethacrylate (PMMA) bone cement and introduced as a local drug delivery system for gentamicin. Intraoperative swab of the right tibia and tissue specimens taken from the medullary cavity tissue revealed a Gram-positive anaerobic rod. The bacterium was identified as Clostridium clostridioforme (C. clostridioforme) at 99.8% using API rapid 32 A strips (bioMerieux, France). In contrast, matrix-assisted laser desorption/ionization timeof-flight (MALDI-TOF) identification detected C. sphenoides with an identification score of 1.6. For exact species determination, 16S rRNA gene sequence comparisons were performed (GATC, Germany), and the isolated bacterium was identified as C. celerecrescens (99% identity from a 512-nt fragment). Antibiotic susceptibilities were determined by Etest (bioMerieux, France). The bacillus was susceptible to amoxicillin/clavulanic acid (minimum inhibitory concentration [MIC] 2 mg/L), clindamycin (MIC 2 mg/L), imipenem (MIC 2 mg/L), and metronidazole (MIC 0.06 mg/L). To provide broad coverage, a treatment including cefuroxime (1,500 mg three times/day) plus metronidazole (400 mg three times/day) with intravenous administration for 15 days was begun. Twelve days later, the tibia was revised. The bone cement rod was removed and repetitive surgical debridement, including A. Mischnik (&) S. Zimmermann I. Bekeredjian-Ding Department of Infectious Diseases, University of Heidelberg, Medical Microbiology and Hygiene, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany e-mail: alexander.mischnik@med.uni-heidelberg.de