[Objective]The purpose of the present study was to obtain the pathogenic bacteria and their main biological characteristics of diseased Micropterus salmoides,and provide technical support for clinical disease prevention and control.[Method]Pathological changes of the naturally diseased Micropterus salmoides were observed firstly.After that,bacteria were isolated and identified through Gram staining,biochemical testing and 16S rDNA sequencing analysis.Pathogenicity of the isolate was performed on mice to explore the pathological lesions.Furthermore,PCR and Kirby-Bauer(K-B)disk methods were used to detect the common virulence genes and analyze the drug resistance characteristics of the isolated bacteria,respectively.The draft genome was obtained by second-generation sequencing technology,and its molecular characteristics were analyzed using bioinformatics methods.[Result]Swollen hepatocytes,vacuolar degeneration and hemorrhagic necrotic lesions were observed in the naturally infected Micropterus salmoides.A dominant bacterial strain was isolated from the diseased Micropterus salmoides,which exhibited milky white,semitransparent,and with a diameter of approximately 1 mm colony and β hemolysis on the blood plate.Gram staining showed negative short bacilli,with blunt and round ends.Through biochemical tests and 16S rDNA sequencing,it was confirmed that the isolated strain was Aeromonas caviae,which was named SCMS.The mortality rate of experimental mice was 100％within 24 h after inoculation with SCMS.And the pathological characteristics were similar to those of naturally infected Micropterus salmoides.Nine virulence genes were detected in the SCMS strain,including Aha,Ahp,Aer,Alt,gcaT,Act,Exu,Ela and eprCAI genes.Drug sensitivity test results showed that the isolated bacteria showed resistance or moderate sensitivity to most tetracycline and macrolide drugs.The whole genome sequencing showed that the isolated strain had a total length of 4 329 602 bp and a GC content of 61.5％.The genome information was registered as JARFUQ000000000 in GenBank.Similarity analysis showed that the isolated strain had high similarity with human and food sources of Aeromonas caviae.The comparison of Virulence Factor Database(VFDB)showed that the isolate strain carried multiple virulence genes related to adhesion,invasion,and secretion systems etc.Also,7 drug resistance genes were harbored in the isolated strain when annoted by the drug resistance gene database(CGE).Inconsistency phenomenon was found between partial genes and its drug resistance phenotypes.[Conclusion]In this experiment,virulence and drug resistance genes of an Aeromonas caviae strain isolated from diseased Micropterus salmoides were analyzed through whole genome sequencing technology,and all these findings could provide technical support for clinical disease prevention and control of Micropterus salmoides.
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