Abstract Background Bloodstream infection (BSI) is a constant threat for hospitalized patients, and elderly patients are particularly susceptible to BSI caused by anaerobic bacteria. Changes in the gut microbiota composition may lead to pathogen overgrowth and translocation into the bloodstream. Consequently, domination of specific taxa in the intestinal bacterial community seems to be associated with a higher risk of bacteremia in some patient populations. Case presentation Here, we report the case of a 90-year-old heart failure (HF) patient who was admitted to the hospital for an acute state of cardiac decompensation. Twenty days after admission, he was febrile to 38.2 °C whereas his white blood count and C-reactive protein increased to 6190 cells/μL and 31.2 mg/L, respectively. Of the patient’s blood culture (BC) bottle pairs collected under the suspicion of infection, the anaerobic bottle yielded an organism that was later identified as Prevotella copri. Concomitantly, the patient’s fecal sample was obtained for the intestinal microbiota characterization by sequencing the V3/V4/V6 regions of the bacterial 16S rRNA gene. The analysis revealed highest relative abundances of Bacteroidales (34.1%), Prevotellaceae (19.0%), Prevotella (15.2%), and P. copri (6.1%) taxa, indicating that the patient’s gut microbiota was dominated by Prevotella organisms. The patient was successfully treated with metronidazole, and was discharged to a long-term care facility at 35 days of admission. Conclusions We provide the first evidence for a clinically significant BSI caused by P. copri and its relationship to a Prevotella-rich gut microbiota in the HF patient setting. When strengthening the pathogenicity of P. copri, the present case suggests that the gut may be a source of BSI caused by the rare anaerobic organism. Future studies are necessary to assess the role of the gut microbiota profiling for precise identification and targeted treatment of patients at high risk of BSI.