Background Enterococcus faecalis (E. faecalis) is a well-known bacterium that colonizes the human gastrointestinal (GI) tract. It is most recognized for causing antibiotic-resistant bacteremia, pneumonia, intra-abdominal infections, and endocarditis. Overgrowth in the gut and translocation to the bloodstream through the intestinal epithelium is the widely accepted mechanism for developing E. faecalis bacteremia, although the mechanisms of invasion, survival, and virulence continue to be investigated.

Case Presentation A 37-year-old man with a past medical history of acute monocytic leukemia (AML), hypertension, and type II diabetes mellitus presented to the hospital with worsening chills, diffuse muscle aches, increased drainage from mouth sores, subjective fevers, and increasing fatigue six days after completing a 7+3 chemotherapy regimen with daunorubicin/cytarabine. The patient had gingivostomatitis predating his official AML diagnosis. Febrile neutropenia was suspected due to the patient's symptoms and pancytopenia with prolonged and profound neutropenia. Blood cultures from admission grew E. faecalis repeat blood cultures were negative, and no aerobic bacteria were visualized. Respiratory cultures, Legionella antigen, rapid influenza A and B, and COVID-19 PCR tests were all negative. The patient was initially empirically treated with cefepime, then switched to piperacillin/tazobactam. When susceptibilities from the initial blood culture showed that E. faecalis was pan-sensitive, the patient was discharged on an oral regimen of amoxicillin for 14 days. Repeat blood cultures were negative within 48 hours of discharge. A transthoracic echocardiogram showed no evidence of vegetations, and there was low suspicion for infective endocarditis.

Discussion There have been few documented cases of E. faecalis associated with underlying colorectal malignancies and the development of infective endocarditis. However, there are no documented cases where E. faecalis was identified in the bloodstream and treated before complications (e.g., infective endocarditis) developed. The scarcely documented cases of pan-sensitive E. faecalis make this case unique. The translocation of E. faecalis from the GI tract to the bloodstream is possibly more likely during induction chemotherapy with daunorubicin and cytarabine, which damage the gastrointestinal epithelium and cause painful oral mucositis and diarrhea. In combination with the neutropenia induced by this treatment, it is very likely that this patient’s AML chemotherapy regimen led to his E. faecalis infection. The feasibility of gut-protective measures during intensive chemotherapy induction to reduce translocation of gastrointestinal infections is an area needing further investigation. The patient’s rapid recovery from this infection and its pan-susceptibility is unusual and resulted in an excellent outcome.