Identification and susceptibility test of pathogenic Aeromonas schubertii isolated from Siniperca chuatsi

Abstract:

[Background] Aeromonas schubertii is ubiquitous in fresh water, seawater, and sediment. The pathogenic strains have been prevalent in cultured Channidae fish in China and infected other economic fishes, leading to death outbreak. [Objective] The pathogen was isolated and identified from the diseased Siniperca chuatsi. The pathogenicity and drug sensitivity of the isolate were determined, thereby providing references for the clinical treatment of this disease.[Methods] The spleen and kidney tissues of the diseased S. chuatsi were collected for polymerase chain reaction (PCR) or real-time PCR (RT-PCR) amplification of common viruses. The liver and ascites of the diseased S. chuatsi were pooled for the bacterial isolation and cultivation. The gyrB, 16S rRNA and virulence genes of the representative strain were amplified by PCR, and their physiological and biochemical characteristics were identified. The susceptibility test and the artificial infection test were carried out. [Results] The detection results of infection spleen and kidney necrosis virus, Siniperca chuatsi ranairidovirus and Siniperca chuatsi rhabdovirus in the diseased S. chuatsi were negative, but large amount bacteria were observed from the liver and ascites. The representative strain Gui210820 was confirmed as A. schubertii, and carried the virulence genes of hemolysin, aerolysin, elastase and lipase. The median lethal concentration (LD₅₀) of S. chuatsi infected by peritoneal injection was 3.16×10⁵ CFU/mL. The Gui210820 strain was resistant to 6 kinds of antibiotics such as tetracycline, kanamycin, and cotrimoxazole, and sensitive to 11 kinds of antibiotics, including doxycycline, enrofloxacin, neomycin, and florfenicol.[Conclusion] In this study, pathogenic A. schubertii has been isolated from the tissues of the diseased S. chuatsi. Aquatic approved drugs enrofloxacin, neomycin, and florfenicol can be used for the clinical treatment of this bacterial disease.

Key words:Siniperca chuatsi;Aeromonas schubertii;virulence genes;pathogenicity;drug susceptibility