Rare infection of Psychrobacter arenosus in Aristichthys nobilis and its zoonotic potential

During a survey of diseased Aristichthys nobilis in Yanxi Lake, Wuhan, China, isolate YXHB202404 was identified as Psychrobacter arenosus through 16S rRNA gene sequencing, whole-genome sequencing, morphological observation, and biochemical analysis. The presence of 16 temperature-regulating genes that have been reported in this strain correlates with its capability to proliferate across a wide temperature range of 4–37 °C. Artificial infection trials in Carassius auratus demonstrated its high pathogenicity with LD 50 values of 2.96 × 10 3 CFU/g at 16 °C and 7.43 × 10 3 CFU/g at 28 °C. Challenged fish exhibited haemorrhage and ascites with multi-organ damage. P. arenosus YXHB202404 caused mortality rates of 33% in healthy mice and 100% in immunosuppression mice at an inoculation dose of 1.95 × 10 7 CFU/g, accompanied by severe histopathological lesions and inflammatory response. Antimicrobial susceptibility testing indicated resistance to vancomycin and erythromycin but sensitivity to florfenicol, enrofloxacin, and doxycycline. This work provides the first evidence identifying P. arenosus as a high pathogenic agent for fish. The zoonotic potential of P. arenosus underscores the critical importance of ongoing surveillance for psychrophilic bacteria.