Identification and histopathological and pathogenicity analysis of Aeromonas salmonicida salmonicida from goldfish (Carassius auratus) in North China

Abstract

In this study, bacterial pathogens were isolated from the liver, spleen, kidney, heart, and muscle of diseased goldfish (Carassius auratus) after a massive outbreak of disease in an aquaculture farm in Anshan, Liaoning Province, North China (N41°05′58.42″ E122°53′31.89″). Based on physiological and biochemical characterization of the bacteria and 16S rDNA sequence analysis, the bacterial isolates were identified as Aeromonas salmonicida salmonicida. Virulence gene multilocus sequence typing analysis showed that the bacterial isolates from all the organs collected were of the same type, and clustered in the same phylogenetic group as A. salmonicida salmonicida. The pathogen, was named AS.17 and was resistant to rifampicin, bacitracin, vancomycin, penicillin and compound sulfamethoxazole, but was highly sensitive to nalidixic acid, lomefloxacin, spectinomycin, ofloxacin, and ciprofloxacin. Goldfish experimentally infected with AS.17 had similar symptoms to naturally infected fish, including gill filament anemia, intestinal bleeding, intra-abdominal fluid, and jaw bleeding. Histological analyses showed that the liver, the spleen, the kidney and the intestines of fish infected with AS.17 had severe pathological alterations. In summary, this study reports the isolation of A. salmonicida salmonicida from C. auratus in North China and provides a reference strain and a research foundation for further studies on A. salmonicida disease control and epidemiology. Keywords: Aeromonas salmonicida salmonicida, Carassius auratus, Histopathology, Identification, MLST, Pathogenicity