Robinsoniella Bacteremia in a Patient With Radiation Proctitis and Prior Colon Cancer: A Rare Case.

Robinsoniella species are strictly anaerobic, Gram-positive, spore-forming bacilli infrequently associated with human bloodstream infections. We present a case of a 49-year-old woman with a history of colon and anal carcinoma treated with radiation and chemotherapy. She presented with fever, dyspnea, and worsening diarrhea. Blood cultures grew Serratia marcescens, Robinsoniella species, and Clostridium species, and she was initially treated with intravenous piperacillin-tazobactam and vancomycin, followed by cefepime, before ultimately transitioning to ertapenem. Although no treatment is currently established for Robinsoniella peoriensis, evidence remains insufficient to define an optimal antimicrobial regimen. This case highlights the pathogenic potential of Robinsoniella species in immunocompromised patients and underscores the importance of considering gastrointestinal pathology as a source of bacteremia involving this uncommon anaerobic organism.