Relevance in question: A rare case of Actinomyces radicidentis bacteremia.

Background: Actinomyces spp.-associated bloodstream infections have been infrequently described and repeatedly but not exclusively associated with intra-oral infections. For Actinomyces radicidentis, which has been shown to cause biofilm-forming endodontic infections, bacteremia has only once been reported so far. To elaborate on the scarcely available information on potential etiological relevance of A. radicidentis as a cause of bloodstream infection, we describe another case of A. radicidentis bacteremia. Case report: A. radicidentis confirmed by 16S rRNA gene sequencing was detected in the bloodstream of an 81-year-old male multimorbid patient with diffuse large B-cell lymphoma of non-germinal center type under chemotherapy as the most critical medical condition. A specific focal infection was not recorded. A concomitantly diagnosed Pseudomonas aeruginosa-associated urinary tract infection was treated with piperacillin/tazobactam for 1 day and meropenem for additional 9 days. While the course of the infection was considered as favorable by the clinicians in charge, an unfavorable course of the underlying malignant disease let to demission of the patients for palliative care at home. Discussion: Although A. radicidentis bacteremia was not specifically addressed, negative effects on the clinical course were not confirmed. Conclusions: The etiological relevance of A. radicidentis bacteremia in patients without specific infectious foci remains uncertain.