ISOLATION AND CHARACTERIZATION OF AEROMONAS SALMONICIDA SUBSPECIES SALMONICIDA FROM LARGEMOUTH BRONZE GUDGEON (COREIUS GUICHENOTI) CAGE-CULTURED IN THE UPPER REACHES OF YANGTZE RIVER

Largemouth bronze gudgeon (Coreius guichenoti) is a potamodromous and endemic fish in the upper reaches of Yangtze River. An epidemic was found in largemouth bronze gudgeon at a farm in Luzhou, Sichuan province, southwest China, at the end of March 2012. In this study, we reported the first observation of furunculosis found in largemouth bronze gudgeon. One dominant bacteria strain, YTL1, was isolated from the liver of diseased largemouth bronze gudgeon, and a series of methods including morphological observation, biochemical tests, and phylogenetic analysis of 16S rRNA and six housekeeping genes were used to identify the pathogen. The strain was finally identified as A. salmonicida subsp. salmonicida based on the results. Antimicrobial susceptibility tests were carried out by the standard Kirby-Bauer disc diffusion method to screen effective drugs for the therapy of the disease, with results showing that YTL1 was sensitive to thirteen antibiotics such as florfenicol, norfloxacin, and ampicillin, resistant to 6 antibiotics such as bacitracin, streptomycin, and kanamycin, and mid-sensitive to erythromycin. Accordingly, florfenicol was added into diets to control furunculosis in largemouth bronze gudgeon with a good result. Artificial infection experiments in grass carp fingerlings and zebrafish resulted in the similar symptoms as diseased largemouth bronze gudgeon. In conclusion, our study demonstrated that multilocus sequence typing based on six housekeeping genes is an effective method to identify A. salmonicida strains to the subspecies level, confirmed that A. salmonicida infection is one of the greatest threats to artificial breeding and aquaculture of largemouth bronze gudgeon, and has expanded the susceptible hosts of A. salmonicida subsp. salmonicida to more cyprinid fishes.