Isolation and identification of Aeromonas veronii from diseased Micropterus salmoides

Sudden death occurred in Micropterus salmoides larvae reared on a farm in Foshan, Guangdong Province of China in spring of 2020. To investigate the etiology of this disease, we isolated a strain of bacteria GZXR2020 from the liver tissue of diseased M. salmoides larvae and conducted its molecular identification. We obtained the full-length sequences of the 16S rRNA gene and gyrB gene of the strain by PCR amplification. BLAST results show that the sequences were highly homologous to the corresponding sequence of Aeromonas veronii in GenBank, with homology higher than 99.5% and 98.3%, respectively. Using VITEK2 automatic bacterial identification system and according to the results of a total of 45 physical and chemical identification, sheep blood agar plate hemolysis test that showed β-hemolysis, detection of the virulence genes as well as the physicochemical identification, we identified the bacteria as A. veronii bv. sobria. In the artificial regression infection experiment, intraperitoneal injection of 3×10⁷, 1.5×10⁸ and 3×10⁸ CFU·mL⁻¹ resulted in 7%, 40% and 100% mortality, respectively. The drug sensitivity test of a total of 17 antimicrobial agents shows that the strain GZXR2020 was highly sensitive to seven antibacterial drugs such as spectinomycin, fleroxacin, florfenicol and so on.