Abstract:

The pathogen identification and drug susceptibility test were performed on grass carp (Ctenopharyngodon idellus) that suffered from an acute disease in a fish farm in Gaojialing town, Poyang County, Jiangxi Province in June 2016. The aim was to determine and identify the cause of death and provide reference for effective prevention and control of the disease in future. The pathogenic bacteria were isolated and purified from grass carp with hepatobiliary syndrome by bacterial isolation method under aseptic condition. The morphological, biochemical analysis, 16S rDNA sequence analysis and gyrB sequence analysis were used to identify the strains, and the challenge test was conducted to obtain LD₅₀ of grass carp. The drug susceptibility test was conducted by a filter paper diffusion method. The results showed that a pathogenic bacteria strain was isolated from grass carp. The pathogen was identified as Aeromonas veronii, called PYG1. PYG1 could infect grass fish, and the LD₅₀ was 1.5×10 ⁴CFU/g. The drug susceptibility test showed that the strain was susceptible or moderately susceptible to 9 kinds of drugs, including aminoglycosides, second-generation and third-generation cephalosporins and ofloxacin, and was resistant to other drugs tested, and was a strongly resistant strain. In conclusion, the pathogen of grass carp is A. veronii PYG1, which could be controlled with aminoglycosides, cephalosporins and quinolones.

Key words: grass carp, hepatobiliary syndrome, Aeromonas veronii, isolation and identification, drug susceptibility test