2025

Understanding the genetic characteristics of Aeromonas jandaei in Brazilian aquaculture is crucial for developing effective control strategies against this fish pathogen. The present study conducted a genomic analysis of Brazilian A. jandaei strains with the objective of investigating their virulence potential and resistance profiles. Four Brazilian isolates were subjected to sequencing, and comparative genomic analyses were conducted in conjunction with 48 publicly available A. jandaei genomes. The methods employed included quality assessment, de novo assembly, annotation, and analyses of antimicrobial resistance and virulence factors. The results demonstrated the presence of fluoroquinolone resistance genes within the core genome. Notably, these antibiotics are not authorized for use in aquaculture in Brazil, suggesting that their resistance determinants may originate from other selective pressures or horizontal gene transfer unrelated to aquaculture practices. The analysis identified significant virulence mechanisms, including T2SS, T3SS, and notably T6SS (vgrG3 gene), which was more prevalent in Brazilian isolates. Additionally, genes associated with motility, adhesion, and heavy metal resistance were identified. These findings highlight the enhanced adaptability of Brazilian A. jandaei strains and raise concerns about antimicrobial resistance in aquaculture, emphasizing the need for improved regulatory oversight and control strategies.

Plesiomonas shigelloides is a common opportunistic pathogen of fish that may result in significant economic losses during outbreak periods. The infection is revealed by several clinical signs, including pericarditis, multifocal necrosis, hepatic atrophy, ulcerative lesions and other pathological changes, which may result in a reduction in the number of economically viable animals on fish farms. In humans, P. shigelloides infections are associated with diarrheic cases resulting from the consumption of contaminated food. These facts justify further study of the species pathogenicity, which is not yet well-established owing to the recent taxonomic classification. Considering the aforementioned information, the main goal of this research was to characterize the virulence and antimicrobial resistance factors present in four P. shigelloides strains isolated from aquatic organisms in Brazil. To gain a deeper understanding of the genomic characteristics of the subjects, the following methodology was employed: the genomic similarity of the strains was evaluated through the pyANI method; the phylogenomic evaluation was performed by OrthoFinder; GIPSy software was used for genomic island search; and PanViTa was employed to search for virulence and resistance factors. The results suggest the presence of multiple virulence factors (51) and antimicrobial resistance genes (12) in the genomes of the main isolates. This is the first genomic study of P. shigelloides exploring the potential pathogenicity in Nile tilapia in the northeast Brazil.