Ruminococcus gnavus, an unusual cause of surgical site infection following vertebral posterior instrumentation: a case report

BACKGROUND: Ruminococcus gnavus (R. Gnavus) is an anaerobic Gram-positive coccus, common commensal of the gastrointestinal tract of animals and humans. Anaerobic organisms as etiologic agents of bone and joint infections (BJI) are uncommon and frequently underestimated. New technologies, such as mass spectrometry techniques and molecular techniques like 16S rRNA, allow for more efficient diagnosis of these anaerobic bacteria. We present the first case report of deep surgical site infection (SSI) due to R. Gnavus, following spinal surgery. CASE DESCRIPTION: We report the case of a deep SSI caused by R. Gnavus following posterior spinal instrumentation in an 81-year-old woman. The patient underwent extension of her previous fusion L2-L5, due to adjacent segment disease (ASD). We performed a T10 to S2-alar-iliac instrumentation. During the postoperative period, the patient presented with a paralytic ileus that required the placement of a nasogastric tube followed by gastrointestinal bleeding and two gastroscopies. Subsequently the patient showed signs of deep SSI. We performed surgical irrigation and debridement. All six cultures in anaerobic media showed short Gram-positive diplococci, using matrix-assisted laser desorption/ionization time of flight mass spectrometry (Maldi-TOF MS) all six strains were identified as R. Gnavus. The patient was treated with amoxicilin 1 g/8 h and ciprofloxacin 750 mg/12 h for 4 weeks. Six months postoperative, she was asymptomatic. CONCLUSIONS: As is the case with our patient, all previously described cases of R. Gnavus infection had a history of intestinal disease or immunosupression. We believe the isolation of R. Gnavus should raise the possibility of intestinal injury. Immunosuppression is also an important risk factor for the development of R. Gnavus infection.