Fatal Robinsoniella peoriensis Bacteremia in a Patient With Metastatic Breast Cancer and Severe Liver Failure

Robinsoniella peoriensis is a rare anaerobic, Gram-positive, spore-forming bacillus that has been rarely reported as an opportunistic human pathogen.We report a fatal case of R. peoriensis bacteremia in a 58year-old woman with newly diagnosed metastatic breast cancer, extensive hepatic involvement, severe liver failure, massive ascites, and sepsis.Two anaerobic blood cultures yielded Gram-positive bacilli subsequently identified as R. peoriensis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), with a confidence score of 99.9%.Disk diffusion testing under anaerobic conditions showed inhibition around imipenem, amoxicillin-clavulanic acid, and erythromycin disks, whereas no inhibition was observed around ciprofloxacin, levofloxacin, and ceftriaxone disks.Because no validated species-specific disk diffusion breakpoints are available for R. peoriensis, these findings were interpreted descriptively rather than as standardized susceptible or resistant categories.Despite antimicrobial and supportive therapy, the patient's clinical condition progressively deteriorated, and she died eight days after admission.Given the severity of the underlying metastatic disease and hepatic dysfunction, the fatal outcome cannot be attributed solely to R. peoriensis bacteremia.Severe hepatic dysfunction and impaired host defenses may have contributed to the development of invasive infection; however, the portal of entry could not be established, and gastrointestinal bacterial translocation remains a possible but unproven mechanism.This case also illustrates the contribution of MALDI-TOF MS to the identification of uncommon anaerobic organisms in clinical microbiology.