Isolation and characterization of Citrobacter spp. from the intestine of grass carp Ctenopharyngodon idellus

Citrobacter gastroenteritis became an increasingly significant health problem in intensive aquaculture in China. In this study, three bacterial strains were isolated from the intestinal tract of farmed grass carp (Ctenopharyngodon idellus), and were tentatively numbered C9414, C0520 and C0934, and then they were identified as Citrobacter freundii, C. gillenii and C. werkmanii by the biochemical properties and molecular techniques. The strain C9414, namely C. freundii showed the pathogenicity to mice and zebrafish, respectively. Furthermore, the fingerprint patterns with distinct bands of three isolates were generated by single-strand conformation polymorphism (SSCP) analysis. To our knowledge, this is the first report on the bacteria Citrobacter spp. isolated from the intestine of fish in China.