Flavonifractor plautii bacteremia following bacterial translocation from the gut: A case report and literature review.

A 75-year-old male, hospitalized with back pain, remained hospitalized for tests for unexplained colitis, which was diagnosed as inflammatory bowel disease unclassified and treated with antibiotics and prednisolone, resulting in Clostridioides difficile colitis. Therefore, antibiotics were discontinued, and oral metronidazole treatment was initiated; however, as the patient's fever persisted, blood cultures were performed. An anaerobic bottle of blood culture turned positive the following day. Initial Gram staining of the positive blood culture fluid showed negative rods, and restaining detected small numbers of Gram-positive rods among the Gram-negative rods. The gray colonies on the subculture medium contained only Gram-negative rods. The bacterium was identified as Flavonifractor plautii using mass spectrometry. We ordered the ATCC 29863 F. plautii strain and compared with the strain of this case. The biochemical test result and the change in colony fluorescence under ultraviolet light of the strain isolated from the patient were identical to those of the ATCC strain, supporting the mass spectrometry results. Bacterial translocation from colonic mucosa was suspected, which improved following levofloxacin and metronidazole therapy. Only eight cases of human F. plautii infection have been reported, and we summarized them as a review. Careful and thorough isolation and identification of bacteria that are rarely isolated clinically, such as F. plautii, is crucial in accumulating evidence on rare infectious diseases.