Isolation,Identification and Antibiotic Susceptibility Test of Aeromonas caviae from Common Carp(Cyprinus carpio)

ZHANG Chao; LÜ Jun

doi:10.15933/j.cnki.1004-3268.2025.01.016

Abstract：The research was conducted to clarify the etiology of common carp fingerlings death in a aquaculture farm in Wanzhou District,Chongqing,and provide references for the prevention and treatment of the disease.The pathogen was identified by separation and purification,physiological and biochemical tests,16S rDNA and cpn60 gene detection,phylogenetic analysis,and animal regression infection test.Antibiotic susceptibility test was carried out by disk diffusion method.The results showed that one dominant bacterium strain WZ2302 was isolated from the liver,kidney and spleen of the diseased fingerlings.The isolate was Gram-negative,rod-shaped and both ends were obtuse.The surface of the colony was smooth,with light yellow and semi transparent.The bacteria had motility.The oxidase,arginine dihydrolase,catalase,and indole tests were positive.Glucose(producing acid but no gas),sucrose,esculin,arabinose,mannitol,and salicin could be fermented.16S rDNA and cpn60 gene sequences had the highest homology with Aeromonas caviae,reaching 99％and 98％respectively.The artificial infection symptoms performed similarity to the clinical case.The results of antibiotic susceptibility test showed that the bacteria were sensitive to 13 antibacterial drugs such as enrofloxacin,florfenicol,and ofloxacin;moderately sensitive to ciprofloxacin,streptomycin,and ciprofloxacin;resistant to penicillin,cefalotin,ampicillin and cefoperazone.In summary,the pathogen causing common carp fingerlings death was Aeromonas caviae,and enrofloxacin or florfenicol can be used to prevent and treat the disease.