Isolation, identification and characterization of Aeromonas schubertii from hybrid snakehead (Channa maculata♀ × C. argus♂)

Hybrid snakehead ( Channa maculata♀ × C. argus♂) is one of the most popular species cultured in the areas of eastern and southern China. With high density culture and rapid expanding production, problems of its diseases become more and more serious. A disease with white spots in internal organs of hybrid snakehead broke out in Fushan and Guangzhou in Guangdong Province in 2011. Bacteria pathogens were isolated from diseased hybrid snakehead cultured in pond. Two bacteria strains with strong virulence were chosen for identifications. The morphological, biochemical and physiological characteristics of the two isolates were studied by using conventional method, ATB Expression System(ID32 STREP)and other assays, and the characteristics of the isolated strains were in accordance with those of Aeromonas schubertii. Molecular analyses of 16S rRNA and gyrB genes were used for further identification. BLAST showed that 16S rRNA and gyrB genes of two strains possessed high similarities with their counterparts registered in GenBank and with each other. The virulent tests were carried out by using the pure culture of the isolated strains artificially infected hybrid snakehead, and the result indicated that the high concentration of bacteria (≥1 × 107 CFU/mL) caused acute death, and infected diseased fish displayed symptom of sarcoidosis after three days, while the control group showed no signs in 7d post-challenge. The morphological and biochemical characteristics of the re-isolated bacteria from the artificially infected diseased fish were the same as those of the original infected bacteria. Antibiotic sensitivity assays showed that among 16 antibiotics tested 14 were sensitive,and 2 were resistant.