A Case of Necrotizing Fasciitis Caused by Mixed Infection of Arcanobacterium haemolyticum and Streptococcus agalactiae

<i>Arcanobacterium haemolyticum</i> (<i>A. haemolyticum</i>), a Gram-positive, anaerobic, rod-shaped bacterium, is typically associated with pharyngitis and skin infections but can also cause severe, life-threatening infections such as sepsis and necrotizing fasciitis (NF), particularly in immunocompromised patients. We report a case of severe NF of the lower extremity caused by a mixed infection with <i>A. haemolyticum</i> and <i>Streptococcus agalactiae</i> (<i>S. agalactiae</i>) in a patient with diabetes mellitus. A 51-year-old male with poorly controlled diabetes mellitus presented with extensive swelling, necrosis, and bullae formation in his left lower extremity five days after sustaining a puncture wound. Laboratory tests revealed elevated creatine kinase and inflammatory markers, and imaging identified subcutaneous gas. The patient was diagnosed with NF and underwent emergent debridement. Blood and intraoperative tissue cultures grew both <i>A. haemolyticum</i> and <i>S. agalactiae</i>. Despite aggressive surgical management and appropriate antibiotic therapy, the infection progressed, and the patient underwent a below-ankle amputation on hospital day seven and a below-knee amputation on hospital day 29. Antimicrobial therapy was concluded on day 32. This case underscores the potential for <i>A. haemolyticum</i>, particularly in combination with other pathogens such as <i>S. agalactiae</i>, to cause rapidly progressing and life-threatening NF, particularly in patients with underlying risk factors such as poorly controlled diabetes mellitus.