Isolation, Identification, Drug Sensitivity, Pathogenicity and Genomic Analysis of Vibrio mimicus from Pelteobagrus fulvidraco.

In this study, pathogenic bacteria were isolated from diseased Pelteobagrus fulvidraco collected from a yellow catfish farm in northern China. The recovered isolate was subjected to Gram staining, transmission electron microscopy observation, 16S rRNA gene sequencing and whole-genome sequencing, followed by systematic analyses of its antimicrobial resistance, pathogenicity and genomic characteristics. Combined with artificial infection assays and multiple comparative verifications, the pathogen was identified as Vibrio mimicus. Clinical observation of naturally infected fish revealed that superficial skin ulcers of varying severity constituted the hallmark clinical sign of this disease. Genomic analysis uncovered major virulence-related genes, including tlh, vmh and tdh, as well as key antimicrobial resistance genes such as crp and ugd. Artificial infection trials confirmed the strong virulence of this isolate against P. fulvidraco, with distinct clinical manifestations triggered by injections of bacterial suspensions at different concentrations. Mortality was first observed in the high-dose group at 2-3 days post-injection, yet no cutaneous ulceration was detected at this stage. The peak incidence and mortality occurred between 3 and 7 days post-challenge, with diseased fish exhibiting lesions identical to those seen in naturally infected individuals. The median lethal dose (LD50) of the isolate was determined to be 1.72 × 105 CFU/mL. Growth gradient assays across varying temperatures and pH values identified the optimal culture conditions for this strain: 33 °C and pH 8.5. Antimicrobial susceptibility testing demonstrated that the isolate was highly susceptible to piperacillin, norfloxacin, roxithromycin, azithromycin, furazolidone, ceftriaxone and tetracycline, whereas it displayed high-level resistance to compound sulfamethoxazole and clindamycin. Collectively, this work lays a scientific foundation for the isolation, identification and comprehensive research of Vibrio mimicus-induced ulcerative disease in yellow catfish.