The Amazonian aquaculture industry faces significant challenges from Aeromonas hydrophila infections affecting Colossoma macropomum (tambaqui), a key economic species in the region. This study characterized the pathogenicity of Peruvian strain FO129–7 t hrough experimental infection and genomic analysis.
Juvenile tambaqui were challenged with 3-7 × 108 CFU/fish, showing a LD 50-96h of 5.91 × 108 CFU/fish (Figure 1), among the highest reported for serrasalmids. Clinical signs ( Table 1) appeared at 12-24h post-infection, with histopathological revealing necrosis in spleen, liver and kidney.
Genomic analysis revealed eight virulence genes (aer A, fla , hly , ser , lip , alt , act and ahyB). Although elastase (ahyB) showed disruptive substitutions potentially reducing tissue damage, the hemolysin (hly ) exhibited 43.3% sequence divergence without deleterious mutations but with α- hemolysis (vs. β- hemolysis in virulent strains), suggesting expression-level modulation. While these findings indicate FO129–7’s attenuated virulence stems from combined elastase impairment and modified hemolysin expression, future transcriptomic studies should verify the exact regulatory mechanisms involved.
These results identify FO129–7 as a promising candidate for live-attenuated vaccine development due to its balanced immunogenicity profile (completed yet attenuated virulence factors), providing new insights for controlling aeromoniasis in Amazonian aquaculture.