From inference to proof: nanopore sequencing confirms zoonotic Neisseria Zoodegmatis peritonitis after cat bite-related contamination in a patient on automated peritoneal dialysis.

Peritoneal dialysis (PD)-associated peritonitis caused by zoonotic pathogens is uncommon and diagnostically challenging. Neisseria zoodegmatis, a Gram-negative coccobacillus residing in the oral flora of cats and dogs, has been reported only once previously in PD-associated peritonitis, with zoonotic transmission inferred but unproven. We report the case of a 90-year-old patient receiving automated PD who developed peritonitis following cat bite-related transfer-set damage, with partial response to empirical therapy and subsequent relapse. Conventional culture and MALDI-TOF mass spectrometry identified N. zoodegmatis, confirmed by 16S rRNA gene sequencing from colony isolates and PD effluent. Intermediate β-lactam susceptibility prompted escalation to carbapenem-based therapy. Third-generation nanopore sequencing demonstrated N. zoodegmatis as the dominant organism in PD effluent and identified the identical species in feline saliva, establishing molecular concordance. Sustained remission required strict environmental control. This is the second reported case of Neisseria zoodegmatis PD-associated peritonitis and the first one with molecular proof of zoonotic transmission, highlighting the selective role of long-read sequencing in complex or relapsing peritonitis, the need for antimicrobial reassessment after suspicion of pet-related contamination, and the importance of environmental intervention in preventing recurrence.