Isolation, identification and virulence genes detection of pathogenic bacteria from Palea steindachneri with bacterial septicemia

In order to provide reference for effective prevention and control of the bacterial septicemia of Palea steindachneri, the present experiment was conducted to investigate the pathogen of P. steindachneri with bacterial septicemia and the presence of six virulence genes. The pathogen was isolated from the heart and liver tissues of P. steindachneri by using conventional methods, and the pathogenicity of the strains was confirmed by artificial infection. Then the pathogen was identified based on API 20NE bacteria identification system and PCR amplification of 16S rRNA gene. Presence of virulence genes was determined using the polymerase chain reaction. Results showed that four dominant strains named SRB125, SRB142, SRB143 and SRB345 were isolated from the heart and liver tissues of diseased P. steindachneri. The mean fatality rate of healthy P. steindachneri was 97.50%–100.00% and the pathogenic bacteria of bacterial septicemia ofP. steindachneri were the four isolated strains. According to the biochemical and molecular identification results, the four isolated strains were all Aeromonas hydrophila, and they had the closest genetic relationship with A. hydrophila L3-5 (KP716701), sharing homology of 99.9%. The four strains contained two virulence genotypes, hly⁺Aer⁺Alt⁺Act⁺ahal⁺ahp⁺ and hly⁺Aer⁺Alt⁺Act⁺ahal⁺ahp^–, each accounting for two strains. Strain SRB143 from Nanning City and SRB345 from Guiping City all lacked gene ahp.