Isolation and Identification of Aeromonas spp. from Diseased Stinging Catfish and Tiger Shrimp, and Evaluation of Their In Vitro and In Vivo Virulence in Tilapia

Aeromonas spp. are emerging aquatic pathogens responsible for major economic losses in aquaculture and pose potential zoonotic threats to humans. This study focuses on the isolation, molecular characterization, and virulence assessment of Aeromonas spp from diseased freshwater fish and shrimp Bangladesh. Molecular identification was performed by sequencing 16S rRNA gene using 27F–1492R primers. The virulence activities of isolated bacteria, such as flagellar motility, gelatinase and phospholipase, biofilm formation were also examined for the isolated bacterial strains. Our sequence data confirmed that Aeromonas spp infected the sampled freshwater fish. The Aeromonas spp cultured on LB₀ soft agar medium exhibited pronounced swimming motility, with colony expansion increasing from 1.2 cm at 12 h to 3.3 cm at 24 h. In contrast, the Shrimp isolate cultured on LB₅ soft agar medium showed minimal movement, plateauing at 0.7 cm after 16 h, suggesting salt-mediated motility suppression. Gelatinase assays indicated moderate enzymatic activity for the A. media with the ratio between clearance zone and colony diameter ranged from 1.57–1.67, phospholipase activity ranged from 1.41–3.47 and moderate activity in biofilm formation. Therefore, the molecular and in vitro virulence evidence highlights the pathogenic versatility of these isolates and their implications for both freshwater fish disease and public health surveillance.

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