Isolation, identification and pathogenic characteristics of Chryseobacterium sp. from Rana catesbiana

Abstract:

[Background] Diseases, especially bacterial diseases have been a big challenge in American bullfrog (Rana catesbiana) farming. Due to a high diversity of these pathogens, rapid spread of the disease as well as high mortality rate, the bacterial disease in the bullfrog is difficult to prevention and control. [Objective] In order to study the taxonomic status and pathogenicity, one bacterial strain NW1203 was isolated and identified from diseased R. catesbiana. [Methods] The strain NW1203 was isolated from R. catesbiana by streaking plate method under aseptic conditions, followed by morphological observation, physiological, biochemical tests and 16S rRNA gene phylogenetic analyses to identify bacterial species. To investigate the pathogenicity of these bacteria, artificial infection followed by hemolytic test and histopathological examination were performed. [Results] Based on the characterization of physiological, biochemical examination and 16S rRNA gene sequence alignment, the isolated bacteria NW1203 was identified as Chryseobacterium sp. with 100% sequences similarities to Chryseobacterium sp. F30. Furthermore, phylogenetic trees showed bacteria NW1203 was grouped with Chryseobacterium sp. Hemolytic tests showed the strain NW1203 exhibited strongly hemolytic to the erythrocyte of sheep, mice and bullfrog. Artificial infection test and tissue section observation of infected frogs indicated the strain NW1203 had strongly pathogenic to R. catesbiana with LD50 values of 4.753×103 CFU/g and could cause severe pathological changes in main tissues including liver, kidney and spleen. [Conclusion] This study indicates that the bacteria strain NW1203 was a new pathogen causing bacterial disease of R. catesbiana and provides a theoretical basis for the prevention and control of bullfrog diseases.