Isolation,identification of Aeromonas veronii in Acipenser dabryanus and its histological observations

ObjectiveThe present experiment was conducted to investigate pathogenic bacteria that caused death of Acipenser dabryanus and its susceptibility in order to provide references for the clinical diagnosis and scientific prevention of the disease.MethodBacterial isolates were collected from gill,heart,liver and intestines of diseased A. dabryanus by conventional methods. After being purified,the pathogen was identified based on morphological observation,biochemi-cal characteristics together with 16S rRNA sequence analysis. The pathogenicity and histological characteristics of patho-genic bacteria were determined by artificial infection. Drug susceptibility was detected by Kirby-Bauer disk diffusion method.ResultA dominant strain(AD-AV201606)was isolated from the liver tissue of the diseased A. dabryanus . The pathogenic bacteria was finally identified as Aeromonas veronii after morphological observation. Biochemical characteris-tics test together with 16S rRNA sequence analysis. The infection symptoms of the fishes by artificial infection germs ap-peared the same as the natural infection,with mortality rate of 50%-80%. The infected A. dabryanus died 1-3 d after infec-tion. Drug sensitivity test showed that the isolated bacterium was highly sensitive to seven kinds of antibiotics including gentamicin,streptomycin,levofloxacin,tetracycline,ciprofloxacin,azithromycin and cefuroxime. The bacterium had re-sistance to penicillin and rifampicin. The histological changes of sturgeon caused by A. veronii infection were mainly con-centrated in the liver,intestinal tract and gill tissues.ConclusionA. veronii had strong pathogenicity on A. dabryanus . It leads to body damage and even death of A. dabryanus by causing pathological changes in liver,intestine and gill. Genta-micin,streptomycin and tetracycline can be selected for prevention and treatment of the disease in production.