Identification and characterization of pathogenic <em>Aeromonas hydrophila</em> isolated from clinically diseased Chinese rice-field eel, <em>Monopterus albus</em>

Abstract

<em>Aeromonas hydrophila</em> is recognized as a prevalent pathogenic bacterium in aquaculture. An outbreak of a disease characterized by a high mortality rate has been reported at a Chinese rice-field fish farm (<em>Monopterus albus</em>) located in Hubei Province. This study isolated a causative <em>A. hydrophila</em> strain (YFI-C1) in diseased <em>Monopterus albus</em> through bacterial isolation and subsequent morphological, physiological, biochemical, evolutionary and molecular biology analysis. Ten virulence genes, including those that encode cytotoxic enterotoxins (act and alt), a quorum sensing-controlled virulence factor (<em>LuxS</em>), a temperature-sensitive protease (<em>eprCAI</em>), serine proteinase (ser), haemolysin-aerolysin (<em>aeraA</em>), nuclease (<em>nuc</em>), hemolysin (<em>hlyA</em>), lipase (<em>lip</em>), flagellin (<em>fla</em>) have been shown to be responsible for YFI-C1's pathogenicity. An artificial infection was utilized to evaluate the pathogenicity of YFI-C1, with a median lethal dose (LD50) of 1 × 106 colony forming units (CFU)/mL. The Kirby-Bauer test was used to measure YFI-C1's sensitivity to ten antibiotics. According to the findings, YFI-C1 was resistant to Cefothiophene but extremely susceptible to six antibiotics: Ciprofloxacin, Trimethoprim-sulfamethoxazole, Doxycycline, Enrofloxacin, Compound sulfamethoxazoles, and Flufenicol. The results of this study offer valuable insights for future research on bacterial disease prevention and treatment in <em>Monopterus albus</em>.