Phenotypic and genomic characterization of Aeromonas veronii from Thai rugose frog (Hoplobatrachus rugulosus)

Abstract

The farming of the Rugose frog (Hoplobatrachus rugulosus) is of considerable economic importance in Thailand; however, bacterial diseases, particularly those associated with the genus Aeromonas, continue to result in significant production losses. This study represents the report of Aeromonas veronii associated with disease in H. rugulosus in Phayao province, Thailand. The objective was to isolate and characterize the phenotypic and genomic bacterial pathogens from diseased frogs. The identification was conducted using morphological characterization, Gram staining, 16S rRNA gene sequencing, and whole-genome sequencing (WGS). Clinically, infected frogs exhibited external signs including erythema, swelling of the digits, and emaciation, while no obvious internal lesions were observed. The isolate demonstrated β-hemolytic activity and was confirmed as a Gram-negative bacterium. Therefore, the isolate was identified as A. veronii strain Fsp5. Whole-genome analysis revealed a genome size of approximately 4.7 Mb and identified numerous virulence-associated genes, as annotated using the Virulence Factor Database (VFDB), including genes related to adhesion, secretion systems, motility, and regulatory functions. These findings establish the pathogenic potential and genomic features of A. veronii Fsp5 in H. rugulosus, providing a reference isolate to enhance our understanding of Aeromonas infections in cultured frog species. GRAPHICAL ABSTRACT HIGHLIGHTS Aeromonas veronii strain Fsp5 is the first reported pathogenic bacterium associated with diseased frogs (Hoplobatrachus rugulosus) in Thailand. Whole-genome sequencing revealed 169 virulence-associated genes. These findings provide essential baseline genomic data to support improved diagnostics, disease surveillance, and control strategies in frog aquaculture.