Characterization of pathogenicity and Antimicrobial Resistance on the Aeromonas veronii Isolated from Imported Guppies (Poecilia reticulata) Exhibiting scale protrusion disease

This study investigated the pathogenic and antimicrobial resistance characteristics of Aeromonas veronii isolated from imported guppy (Poecilia reticulata) exhibiting dropsy symptoms in a hatchery in Gunsan, Korea. The affected fish showed scale protrusion, hemorrhage, and abnormal swimming behavior, with approximately 80% cumulative mortality. The isolate was identified as A. veronii using 16S rRNA sequencing, species-specific PCR, and gyrB gene analysis. Pathogenicity was evaluated by immersion challenge, resulting in dose-dependent mortality. At 3.2 × 10⁵ CFU/mL, 60% mortality was observed, and the LD₅₀ was estimated to be ≤ 3.2 × 10⁵ CFU/mL. The strain harbored virulence genes including act, aerA, and hlyA. Antimicrobial susceptibility testing based on CLSI (2018) guidelines indicated reduced susceptibility to several antibiotics. Notably, resistance was inferred for Meropenem and Ciprofloxacin based on inhibition zone diameters. The tetracycline resistance gene tet(A) was also detected. These findings suggest that imported ornamental fish may serve as reservoirs of antimicrobial-resistant A. veronii, highlighting the need for continuous surveillance and prudent antimicrobial management in aquaculture.