Human bacteraemia caused by Pseudomonas plecoglossicida, a fish pathogen of ayu (Plecoglossus altivelis): a case report.

Pseudomonas plecoglossicida is a gram-negative bacterium that primarily infects fish and is the causative agent of bacterial haemorrhagic ascites in ayu (Plecoglossus altivelis). Although sporadic human infections such as pneumonia and meningitis have been reported in recent years, human bacteraemia caused by P. plecoglossicida has not yet been documented. Here, we report the first known case of P. plecoglossicida bacteraemia in an 89-year-old male with a history of gastrectomy and recurrent adhesive intestinal obstruction. Following treatment for intestinal obstruction and aspiration pneumonia, including a 7-day course of cefmetazole, the patient developed fever and chills. Blood cultures yielded P. plecoglossicida, which was identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), whereas urine and sputum cultures yielded Escherichia coli and methicillin-resistant Staphylococcus aureus, respectively. Antimicrobial therapy was escalated to meropenem and subsequently de-escalated to ceftazidime based on susceptibility testing, resulting in prompt clinical improvement and complete resolution of the infection. Although the relevance of bacterial replacement phenomena observed in ayu aquaculture to human infection remains speculative, bacteraemia in this case was presumed to result from bacterial translocation associated with intestinal obstruction and disruption of the intestinal microbiota following recent antibiotic exposure. This case suggests that P. plecoglossicida may act as an opportunistic pathogen in patients with disrupted gut microbiota or anatomical vulnerabilities.