Pathogenic characterization of <i>Aeromonas</i> in infected farmed <i>Esox lucius</i> from Xinjiang, China

This study aimed to identify the pathogenic bacterial characteristics associated with diseased Esox lucius. The bacterial 16S rRNA V3–V4 variable region was used to generate high-throughput sequencing data from fish organs with significant lesions. Microbiological testing for pathogenic bacteria and regression infection tests were performed. Kirby–Bauer disc diffusion method was employed to evaluate the susceptibility of pathogenic bacteria to 16 antibiotics commonly used in fishponds. Results revealed that diseased fish exhibited raised skin, large petechiae on body surface, pale liver, ruptured kidneys, and ascites. High-throughput DNA sequencing revealed that Aeromonas constituted a prominent component of the microbiota in the liver, spleen, and kidneys of diseased fish. Pathogenic bacteria isolated from diseased fish harbored the following virulence genes: A. hydrophila (hly+, ahp+, aer+), A. sobria (ahp+, ahal+, act+), and A. veronii (ahal+, act+). Co-infection with all five virulence genes (hly+, ahp+, aer+, ahal+, act+) was more pathogenic than infection with any subset of these genes. The five dominant isolated strains exhibited sensitivity to enrofloxacin, ciprofloxacin, chloramphenicol, and doxycycline, however, were resistant to midecamycin, vancomycin, and penicillin. These findings urge aquaculture management strategies emphasizing Aeromonas co-infection surveillance, targeted fluoroquinolone/tetracycline therapies, and biosecurity enhancements to mitigate environmental persistence of multi-virulent strains.