Identification and virulence genes detection of Edwardsiella tarda isolated from Carassius auratus gibelio

Abstract:

[Objective] To confirm the pathogeny that causes Carassius auratus gibelio death in some fish farms in Shanghai, and characterize the virulence genes of the pathogenic bacteria. [Methods] The pathogenic bacteria were confirmed based on the pathogens screening and artificial challenge experiment, and identified according to 16S rRNA, gyrB and rpoB genes sequence and biochemical characteristics. Published nucleotide sequence methods were used to study the virulence genes (fimA, citC, gad, mukF, katB, esrB and sodB) by PCR amplification, and PCR primers for virulence genes. [Results] Strain GY15 isolated from infected ?sh was proved to be the pathogeny to Carassius auratus gibelio. Analysis of the 16S rRNA, gyrB and rpoB gene sequences of the GY15 gave the highest identity (99%) to Edwardsiella tarda. This was further supported by phylogenetic tree and biochemical characteristics. GY15 was identi?ed as E. tarda. Intraperitoneal injection with GY15 could lead to Carassius auratus gibelio death, with a value of the median lethal dose (LD50) of 4.26×105 CFU/ml. GY15 gave positive PCR results for 7 virulence genes. Antibiotic sensitivity test showed that among 35 antibiotics tested, GY15 was sensitive to 15 antibiotics such as enrofloxacin, florfenicol and ofloxacin, but was resistant to 18 antibiotics such as neomycin, acheomycin and cotrimoxazole. [Conclusion] Carassius auratus gibelio was the susceptible host species of E. tarda, which is a new potential threat to carp’s breeding.

Key words:Carassius auratus gibelio, Edwardsiella tarda, Identification, Virulence genes