Isolation, identification and virulence gene of Streptococcus parauberis from cultured turbot Scophthalmus maximus
WANG He, LI Zhanjun, HUANG Hua, XU Xiaoying, HE Jiabei, CAO Ya’nan, ZHAO Qiang
1.Yantai Marine Economic Research Institute, Yantai 264006, China; 2.Shandong Fisheries Development and Resources Conservation Center, Yantai 264003, China
Abstract: In order to explore the causes of diseases characterized by exophthalmos and sepsis in turbot Scophthalmusmaximus with body mass of(195-535)g farmed in Yantai, Shandong Province in 2019, predominant bacterial strains were isolated from moribund individual tissues including kidney, spleen,and brain, and identified by morphological observation, 16S rRNA gene sequence analysis, and specific PCR amplification.Genetic characteristics of the isolated strain were analyzed by virulence genes, and the susceptibility of the isolated strain to 10 categories including 23 antimicrobial dugs was determined using Kirby-Bauer diffusion method.The results showed that the strains isolated from the visceral tissues as Gram-positive cocci named as BH2-4 was identified as Streptococcusparauberis by the physiological and biochemical characteristics of non-hemolytic, acid from sucrose, mannitol, glucose, without being produced from citrate, rhamnose, hydrolysed aesculin, and by 16S rRNA sequence alignment and specific amplification of Streptococcus.The virulence genotype was found to be scpB--bca--bac--lmb--fbsA--cfb--cpsD--pavA--bibA+-sip+-cylE--hylB+.The strain BH2-4 had median lethal concentration(LD50)of 6.9×108 CFU/mL determined in the healthy turbot injected with hormone interaperitoneally at a dose of 6.3×107, 6.3×108, 6.3×109, and 6.3×1010 CFU/mL.The strain BH2-4 was shown to be high susceptible to 6 categories and 14 antibiotics including β-lactams, quinolones, tetracyclines, macrolides, peptides and rapamycin, resistant to 3 categories and 6 antibiotics, including aminoglycosides, sulfonamides and nitrofurans, and intermediately sensitive to norfloxacin, doxycycline and polymyxin B.The findings were reported for the first time the onset of natural infection of fish-sourced Streptococcusparauberis, and the identification of its characteristics can provide basic support for the research of fish-sourced Streptococcusparauberis disease surveillance, precision prevention, and drug control.
2021, Vol. 36 
