Identification and antibiotic sensitivity of pathogen of intussusception disease found in channel catfish Ictalurus punctatus

A strain bacterium(TE090214) isolated from the liver and brain of the diseased channel catfish Ictalurus punctatus with haemorrhage symptom and "intussusception",was characteristically studied by morphological,physiological and biochemical and was proved to be the pathogen of the disease by artificial infection.The pathogenic bacterium was gram negative,rods in shape,non-capsule and gemma,oxidase-positive,orinithine decarboxylase-negative,utilized mannitol,sucrose,arabinose and salicin with production of acid,and fermented glucose with production of gas and hydrolysis esculin.The 16S rDNA of strain TE090214 was amplified,cloned and sequenced,and a sequence of 1537 base pair(bp) was obtained from the bacteria(GenBank accession number GQ184148).The phylogenetic tree constructed by comparing the 16S rDNA sequence of the isolated strain with other relative bacterial species from GenBank databases revealed that the strain TE090214,Aeromonas hydrophila CCM 7232 and Aeromonas hydrophila ayu-Ah0201 constituted a branch.The isolated strain(TE090214) was identified as Aeromonas hydrophila by morphological,physiological,biochemical characteristics and phylogenetic analysis.The strain TE090214 was found to be sensitive to 5 agents including cefoperazone,intermediately sensitive to 3 agents including streptomycin,and resistant to 7 agents including ampicillin during antibiotic sensitivity to 15 antimicrobial agents.