关键词: 大口黑鲈, 维氏气单胞菌, 分离鉴定, 16S rRNA, 病理损伤

Abstract: This study was conducted to investigate the bacterial pathogen that caused the death of Micropterus salmoides farmed in Sichuan Province.Pathogenetic bacterial was isolated from naturally infected Micropterus salmoides by using traditional methods, and the pathogenicity was determined by artificial infection test.The pathogenic isolate was identified by biochemical identification micro reagent tube and 16S rRNA sequence analysis.Its antibiotic susceptibility was tested by Kirby-Bauer discagar diffusion method,and the histopathological characterization of organs of the diseased Micropterus salmoides
was further observed by conventional paraffin section technique.The pathogenic strain MYLY01 was isolated from the diseased Micropterus salmoides and was identified as Aeromonas veronii based on phenotypic characteristics and 16S rRNA sequence analysis.It had an median lethal dose(LD₅₀) of 4.79×10⁸cfu/mL for healthy Micropterus salmoides,and showed the same clinical symptom as the diseased Micropterus salmoides.Drug sensitivity tested results showed that the MYLY01 was sensitive to cefradine,ceftazidime pentahydrate, gentamicin, neomycin and so on, but resistant to doxycycline, tetracycline,amoxicillin and so on.Clinical symptom of the diseased Micropterus salmoides showed ulcer in dorsum and side of the body,congestion and hemorrhage in gill,swelling in liver,spleen and kidney. Histopathological observation showed obvious degeneration,necrosis and inflammation in liver,spleen,kidney and muscles.The findings confirm that A.veronii is the cause of this epidemic which induces the body damages and even death because of the pathological changes in organs,and the neomycin will be used for the control of this disease in the future.

Key words: Micropterus salmoides, Aeromonas veronii, Isolation and identification, 16S rRNA, Pathological lesions