Outbreaks of Streptococcosis associated with Streptococcus iniae in Siberian sturgeon (Acipenser baerii) in China

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• 作者：Meng-ling Deng ; Ze-hui Yu ; Yi Geng ; Kai-yu Wang ; De-fang Chen ; Xiao-li Huang ; Yang-ping Ou ; Zheng-li Chen ; Zhi-jun Zhong and Wei-ming Lai
• 刊名：Aquaculture Research
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：48
• 期：3
• 页码：909-919
• 全文大小：1203K
• ISSN：1365-2109

文摘

Streptococcus iniae has emerged as an important fish pathogen over the past few decades causing high losses in aquaculture farms all over the world. At least 27 species of fish have been documented to be infected by S. iniae, including cultured and wild populations. In August and October 2013, a serious infectious disease characterized by body ulcer, internal organs haemorrhages and nodules showing on epicardium occurred on the Acipenser baerii farms in Ya'an country, China. Histological examination revealed a multisystemic, necrotising inflammatory response that was particularly marked in liver, kidney, heart and brain. Mass mortality (>40%) was observed in infected fish and two Gram-positive cocci (Ab130920 and Ab131025) were obtained from kidneys and livers of diseased fish. Experimental infections with these two isolates resulted in marked symptoms in the sturgeons similar to those observed in natural outbreaks, and the LD₅₀ values of the two isolates were 5.1 × 10⁵ and 6.4 × 10⁵ cfu per fish respectively. The two microorganisms were identified as S. iniae through physiological and biochemical tests, 16S rRNA and lctO gene sequence analysis. Both two isolates showed a similar antibiotic susceptibility, which were sensitive to ampicillin, amoxicillin, cefazolin, amikacin, deoxycycline, florfenicol, azithromycin, ciprofloxacin, vancomycin and resistant to streptomycin, gentamicin, kanamycin, norfloxacin and sinomin (SMZ/TMP). Multiplex PCR assay for virulence genes showed both isolates possessed six main virulence genes: simA, scpI, pdi, pgm, cpsD and sagA genes. These results indicated that S. iniae could act as a pathogen of farmed A. baerii. This is the first report of S. iniae infection associated with mass mortality in A. baerii.