Analysis of the Characteristics of Aeromonas salmonicida Subsp. Masoucida and Salmonicida Strain Isolated from Atlantic Salmon (Salmo salar)

A total of 21 strains of Aeromonas salmonicida subspecies were isolated from Atlantic salmon. Identification using the vapA gene revealed that 11 strains were A. salmonicida subsp. masoucida while 10 strains were A. salmonicida subsp. salmonicida. All 21 strains were facultative anaerobes and tested positive for oxidase activity, casein hydrolysis, and hemolysis. Although variations were observed among the strains in API 20E and 20NE test results, all strains were positive for indole production, acetoin production, gelatinase, and nitrate reduction. Additionally, API ZYM test results indicated enzymatic activity for alkaline phosphatase, esterase, esterase lipase, and leucine arylamidase in all strains. The 11 strains of A. salmonicida subsp. masoucida were susceptible to trimethoprim/sulfadiazine, neomycin, and florfenicol among 19 aquaculture antibiotics tested. In contrast, the 10 strains of A. salmonicida subsp. salmonicida were susceptible to enrofloxacin, ampicillin, ceftiofur, trimethoprim/sulfadiazine, oxolinic acid, ciprofloxacin, neomycin, gentamicin, and florfenicol. These findings provide a foundation for the development of novel preventive and therapeutic measures for bacterial diseases and establishment of effective disease control strategies, thereby contributing to the sustainable growth of the Atlantic salmon aquaculture industry in Korea.