Chen S C, Lin Y D, Liaw L L, Wang P C
Department of Veterinary Medicine, National Pingtung University of Sciences and Technology, Taiwan, ROC.
Dis Aquat Organ. 2001 May 4;45(1):45-52. doi: 10.3354/dao045045.
An epizootic bacterial infection in the giant freshwater prawn Macrobranchium rosenbergii occurred in Taiwan from May to June 1999. The cumulative mortality was approximately 30 to 75%. The diseased prawns showed opaque and whitish muscles and were approximately 2 mo old with total lengths from 5 to 6 cm. Histopathologically, they showed marked edema and necrotic lesions with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Three isolates from diseased prawns at different farms were tested using the API 20 Strepsystem and conventional tests and identified as Lactococcus garvieae. Experimental infections with these isolates gave gross signs and histopathological changes similar to those seen in the naturally infected prawns. The LD50 value of isolate MR1 was 6.6 x 10(5) colony forming units/prawn. Identification of MR1 was confirmed by a PCR assay for L. garvieae that gave the expected amplicon of 1100 bp. In addition, its 16S rDNA sequence (GenBank accession number AF283499) gave 99% sequence identity to Enterococcus seriolicida (synonym L. garvieae; GenBank accession number AF061005). This is the first report of confirmed L. garvieae infection in prawn aquaculture.
1999年5月至6月，台湾地区的罗氏沼虾发生了一种流行性细菌感染。累计死亡率约为30%至75%。患病的虾肌肉呈现不透明的白色，大约2月龄，全长5至6厘米。组织病理学检查显示，它们的肌肉和肝胰腺出现明显水肿、坏死性病变并伴有炎症。使用脑心浸液培养基或胰蛋白胨大豆琼脂分离出的细菌为革兰氏阳性且呈卵形。对来自不同养殖场患病虾的三株分离菌进行了API 20链球菌系统检测和常规检测，鉴定为格氏乳球菌。用这些分离菌进行的实验性感染产生的肉眼可见症状和组织病理学变化与自然感染的虾相似。分离菌MR1的半数致死剂量值为6.6×10⁵菌落形成单位/只虾。通过针对格氏乳球菌的PCR检测对MR1进行鉴定，得到了预期的1100 bp扩增产物。此外，其16S rDNA序列（GenBank登录号AF283499）与杀鱼肠球菌（格氏乳球菌的同义词；GenBank登录号AF061005）的序列同一性为99%。这是对虾养殖中确诊的格氏乳球菌感染的首次报道。
