First Report of Aeromonas veronii as an Emerging Bacterial Pathogen of Farmed Nile Tilapia (Oreochromis niloticus) in Brazil

Brazil is one of the world’s leading producers Nile tilapia, Oreochromis niloticus. However, industry faces a major challenge in terms infectious diseases, as at least five new pathogens have been formally described last years. Aeromonas species are Gram-negative anaerobic bacteria that often fish causing Motile Septicemia (MAS). In late December 2022, an epidemic outbreak was reported farmed tilapia state São Paulo, Brazil, characterized by clinical signs and gross pathology suggestive MAS. The objective this study to isolate, identify, characterize vitro vivo causative agent outbreak. bacterial isolates were identified veronii based on homology 16S rRNA (99.9%), gyrB (98.9%), rpoB gene (99.1%). A. showed susceptibility only florfenicol, while it resistant other three antimicrobials tested, oxytetracycline, enrofloxacin, amoxicillin. lowest florfenicol concentration capable inhibiting growth ≤0.5 µg/mL. phenotypic resistance isolate observed for quinolones tetracycline genetically confirmed presence qnrS2 (colE plasmid) tetA antibiotic-resistant genes, respectively. highly pathogenic juvenile tested vivo, showing mortality rate ranging from 3 100% (1.2 × 104) highest 108) dose groups, To our knowledge, would constitute first report multidrug-resistant associated with outbreaks high rates commercial net cages Brazil.