Unique presentation of an intramuscular abscess caused by Bacteroides pyogenes in the setting of a cat bite: A case report.

Cat bites are a relatively common emergency department presentation. The most common species isolated from cat bite wounds is Pasteurella multocida . In this case report, we discuss a unique case of an intramuscular abscess caused by Bacteroides pyogenes . Antibiotic resistance in Bacteroides species is a growing concern and thus should be treated with caution. We present an 81-year-old female who presented to the emergency department with left calf pain that began 3 weeks prior to the emergency department presentation. She was initially seen by her primary care provider and was prescribed oral Trimethoprim/Sulfamethoxazole and Amoxicillin/Clavulanate. Despite oral antibiotics, she began to have worsening swelling, erythema, and fevers. In the emergency department, the patient's left calf was noticeably erythematous and tender to palpation. Lab work showed a C-reactive protein of 12.4 mg/dl, erythrocyte sedimentation rate of 38 mm/h, and white blood cell count of 15.1. Computed tomography imaging showed an irregularly shaped fluid collection at the junction of the calf musculature and upper aspect of the Achilles tendon. The decision was made to perform an operative incision and debridement on the evening of her presentation. On postoperative day 2, the wound cultures grew positive for both Pasturella multocida and Bacteroides pyogenes . She was subsequently discharged with oral Amoxicillin/Clavulanate 875 mg twice daily for 4 weeks. Further studies can be performed to identify the most efficient ways to isolate and treat this species. This case report emphasizes the importance of ordering both aerobic and anaerobic cultures and aiming antimicrobial therapy against both Pasteurella and anaerobic bacteria.