A 67-year old woman with a past medical history significant for chronic kidney disease and hypertension, sustained a fracture of her right femur in December 2015 requiring a distal femur ORIF. Approximately one month later, the patient was seen for signs of hardware failure and a small superficial abscess at the distal end of her incision. She underwent revision of the ORIF on 20 January 2016. Repeat X-rays demonstrated healing of the fracture. The patient was non-weight bearing and primarily used a wheelchair thereafter.
On 13 May 2016, approximately six months from initial hardware placement, the patient reported to an urgent care clinic with three days of flu-like symptoms associated with aches and chills. She developed swelling in her right leg tracking from her thigh to her knee. She was discharged on oral clindamycin. Over the next several days the lateral lower thigh became swollen and fluctuant. The patient presented to her orthopedic surgeon and underwent an incision and drainage (I&D) of the developing distal femur abscess. Copious amounts of purulent fluid was noted deep in the wound concerning for an infection of her implants. Gram stain yielded gram-positive cocci however cultures remained negative, potentially due to oral antimicrobial exposure prior to sampling. The patient completed a six-week course of intravenous daptomycin dosed at 6 mg/kg every 24 h on 22 June 2016. She received three months of oral doxycycline 100 mg twice daily thereafter.
Radiographic studies revealed signs of a nonunion of the femur, and a fractured rod was noted in July 2016. Antimicrobials were held for two weeks and she was admitted to our hospital on 17 August 2016. The patient was taken back to the operating room for right femur deep hardware removal and debridement of deep tissue and bone. Seven cultures were obtained at multiple sites along the femur bone, hardware plate and tissues surrounding the hardware. On admission, the patient was afebrile and demonstrated a white blood cell count of 11,300 cells/mm3. C-reactive protein was 7.3 mg/L, and the erythrocyte sedimentation rate was 61 millimeters per hour (mm/h).
Vancomycin was initiated on day one of admission and adjusted by serum trough levels accordingly. On day five of hospitalization ampicillin/sulbactam 3 g IV every 6 h was initiated. Six out of the seven cultures obtained from the surgical procedure were all positive for R. peoriensis identified by the 16S ribosomal RNA sequencing. The organism was initially reported by the clinical microbiology lab as an anaerobic gram-positive bacilli. The lab routinely uses MALDI-TOF (matrix assisted laser desorption ionization-time of flight), a mass spectrometry based technology for bacterial species identification. However, it couldn't provide the further result on the isolate most likely due to the limitation of the mass spectrometry database. On day seven the patient had several febrile episodes with a maximum temperature of 101.1  F. The patient's antimicrobials were converted to ertapenem 1 g IV daily and she was discharged on day eight after the fevers resolved. The patient was maintained on a non-weight bearing status. A peripherally inserted central catheter was placed and the patient was then followed by Infectious Disease in an outpatient setting.
The isolate was sent to ARUP laboratories to establish minimum inhibitory concentrations. There are no currently established susceptibility breakpoints specifically for Robinsoniella spp. Antimicrobial susceptibility was tested via a custom panel broth microdilution panel and evaluated using the Clinical and Laboratory Standards Institute (CLSI) breakpoints for gram-positive anaerobes. The strain revealed elevated minimal inhibitory concentrations (MIC) against penicillin (8.0 mcg/mL), and clindamycin (4 mcg/mL) after 48 h of anaerobic incubation using both the Etest and ATB ANA strip. Low MIC's were found for ampicillin/sulbactam (1/0.5 mcg/ml), piperacillin-tazobactam (8/4 mcg/mL), meropenem (0.5 mcg/mL), and metronidazole (0.5 mcg/mL) (Table 1). The patient responded well and completed a six-week course of Ertapenem on 5 October 2016. Laboratory values obtained 14 November 2016 were improved with an ESR of 43 mm/h and C-reactive protein of 0.3 mg/L. On 7 December 2016 the patient underwent a right intramedullary rodding that was uneventful.