Isolation，identification and biological characteristics of Aeromonas veronii from Whitmania pigra

【Objective】To isolate，identify and analyze the biological characteristics of the pathogenic bacteria causing acute death of Whitmania pigra in Taihu breeding base of Jingzhou，Hubei，which could provide theoretical basis for disease prevention and control of W. pigra and promote the healthy development of the breeding industry.【Method】Pathogenic bacteria were isolated and identified from diseased W. pigra. The classification status of the isolated bacteria was determined through morphological observation，physiological and biochemical characteristics analysis，16S rRNA sequence identification and multilocus sequence typing（MLST）. PCR amplification was conducted to identify the presence of virulence genes and drug resistance genes. Drug sensitivity tests were performed using the disk diffusion method to assess the drug resistance，and Chinese herbal medicines bacteriostatic test was conducted.【Result】The results showed that the strain W23 isolated from the edematous parts of W. pigra had high pathogenicity in artificial infection test，and was identified as Aeromonas veronii through morphological observation and physiological and biochemical characteristics analysis. The 16S rRNA sequence identification results indicated that strain W23 had the highest similarity to Aeromonas veronii reference strain and clustered with it in the phylogenetic tree. Detection of virulence genes and drug resistance genes revealed that strain W23 carried 6 virulence genes（whiB3，Fla，Act，Lip，Aer，Ela）and 3 drug resistance genes（blaTEM，tetA，qnrS）. The isolated strain W23 had biofilm formation ability，and the logarithmic growth period was 5-9 h after inoculation. Drug sensitivity tests showed that strain W23 was sensitive to 10 antibiotics，such as polymyxin B，tetracycline and ofloxacin，moderately sensitive to cefalexin and compound sulfamethoxazole，but resistant to 7 antibiotics， including oxacillin，penicillin and cefazolin. The results of antibacterial test in traditional Chinese medicine showed that Prunus mume，Galla chinensis，Schisandra chinensis，Caesalpinia sappan had obvious inhibitory effects on the isolated strain W23.【Conclusion】A. veronii is the pathogenic bacterium causing ascites disease in W. pigra in the Taihu breeding base in Jingzhou，Hubei. It carries 6 virulence genes and 3 drug resistance genes，it has high pathogenicity. In the process of W. pigra culture，P. mume，G. chinensis，S. chinensis，C. sappan can be used to prevent and control the disease caused by A. veronii infection.