Abstract：Two pathogenic bacteria (SS1495 ,and SS1496) were isolated from diseased Scortum barcoo in an aquafarm which was located in Sanshui district of Foshan city , Guangdong province . They were identified by microbial biochemical identification tubes and 16S rDNA sequence analysis ,and the artificial infection experiment and antibiotic susceptibility analysis were performed .The results showed that these two bacteria were facultative anaerobes which were gram negative ,rod in shape ,and motile .They had positive indole ,methyl red and V‐P characteristics ,and utilized glucose ,maltose and mannitol .According to“Bergey’s Manual of Determinative Bacteriology”,the isolates were identified to be Aeromonas hydrophilia based on the morphology ,physiological and biochemical characteristics of the bacteria .The 16S rDNA sequences of the isolates showed a high similarity to that of A .hydrophilia via BLAST network services in NCBI .The median lethal doses for the isolates to healthy S .barcoo were 7 .8 × 104 cfu/g and 3 .9 × 104 cfu/g ,respectively ,indicating they had strong pathogenicity to S .barcoo .The isolates were highly susceptible to cefotaxime ,ciprofloxacin , norfloxacin ,and levofloxacin ,intermediately susceptible to phytomycin ,cephazoline and neomycin ,and resistant to tetracycline ,rifampicin and lincomycin .
