This case report describes a 38-year-old female presenting with a thigh abscess caused by Eikenella corrodens, Actinomyces sp., and α-hemolytic Streptococcus following an intramuscular vitamin B12 injection administered at an outpatient clinic. After failure to improve clinically with intravenous daptomycin and after visualization of the abscess with gas bubbles on CT scan, she was taken to the operating room for three separate surgical irrigation and debridement procedures. Treatment also included intravenous ampicillin/sulbactam followed by oral amoxicillin/clavulanic acid therapy. She remained symptom free and without infection at nine months following hospitalization. It was suspected that poor hygiene played a role in the infection, but a definitive cause was not identified.