Occurrence of tetracycline-resistant Aeromonas hydrophila infection in Korean cyprinid loach (Misgurnus anguillicaudatus)

Abstract

In this paper, we described a mass mortality of cyprinid loaches, Misgurnus anguillicaudatus from a private fish farm in Korea. Diffuse bleeding was observed on the skin around the anal orifice. Bacterial pathogens from kidneys samples of moribund fish were cultured, identified and confirmed to be Aeromonas hydrophila using morphological, biochemical test and genetical analysis. The isolated A. hydrophila strains were resistant to commercial antibiotics and the presence of the tetracycline resistance gene (tet E) was detected by genetical analysis. Pathogenecity test was performed using healthy 4-week-old cyprinid loaches by intraperitoneal (IP) injection and the LD(50) concentration of the pathogen was determined to be 6.0 x 10(7) CFU fish(-1). In this paper, we confirmed the infection of farm-raised cyprinid loaches with tetracycline-resistant A. hydrophila.