Isolation and Identification of Photobacterium damselae subsp. piscicida from Diseased Rock Bream (Oplegnathus fasciatus)

Abstract:

Rock bream (Oplegnathus fasciatus) is an important economic fish cultured in China. In recent years, rock bream aquaculture has developed rapidly along the coast of China. In August 2013, an epizootic occurred among cultured rock bream in a cage culture farm in Zhoushan of Zhejiang Province, China, which caused a cumulative mortality up to 20%. The diseased fish had no obvious symptoms on body surface; the main symptom was characterized by many white nodules (1–2 mm) in the spleen and kidney. The aim of this research was to isolate and identify the bacterial isolate, then to determine the pathogenicity and test drug sensitivity of bacteria pathogen found in diseased rock bream. A dominant bacterium strain OF-1 was isolated from the liver, spleen and kidney. Artificial infection test with intraperitoneal injection method proved that the LD50 value of bacterium strain OF-1 was 5.93×104 CFU/g. It was identified based on the morphology, the biochemical characteristics, and the 16S rRNA sequencing. The results of morphological tests indicated that strain OF-1 was gram-negative, rod bacteria and did not grow in the TCBS plate. OF-1 exhibited an API 20E index profile of 2005004, which was identical with the profile exhibited by Photobacterium damselae subsp. piscicida. The sequence analysis of 16S rRNA gene, the morphological, physiological and biochemical characteristics indicated that the bacterium strain OF-1 could be identified as P. damselae subsp. piscicida. The strain was highly sensitive to gentamicinum, penicillin G, norfloxacin, ofloxacin and ampicillin, but was resistant to erythromycinum, vancomycin, rocephin, streptomycin, kanamycinum and proctaphlin. This paper reported for the first time that P. damselae subsp. Piscicida caused the disease of rock bream in China, which will provide reference in fish health management and disease control.