Epidemiological studies and diagonosis of Streptococcus dysgalactiae isolated farmed fish

从日本产鸡乳球菌（Lactococcus garvieae）市售疫苗免疫培养的琥珀、黄尾细孢杆菌（serola dumerili Risso and yellowtail）、五角细孢杆菌（serola quinqueradiata temmink）和施莱格尔（Schlegel）中分离出Lancefield血清学C组链球菌。分离的细菌为革兰氏阳性球菌，在生理盐水中自动聚集，在生长培养基中形态长链，过氧化氢酶阴性，在血琼脂上α-溶血。测定了分离株（n=2）的16S rDNA几乎完整的基因序列，并与数据库中的菌株进行了比较。根据16S rDNA序列、细菌学性质和Lancefield血清学分型，鉴定分离株为乳糖不良链球菌。设计的16S-23S rDNA基因间隔区特异性寡核苷酸引物扩增出了所有鱼类分离株和α-溶血性抗乳链球菌亚型菌株的一个基因。催乳不良菌ATCC430738和β-溶血性催乳不良菌亚种。而不包括S. equiATCC33398、Lactococcus garvieaeATCC43921和L. garvieae KG94 08。在实验感染的鱼身上观察到的严重病变（尾端坏死）与在自然感染的鱼身上观察到的相似。需要进一步注意区分兰斯菲尔德C群链球菌感染与日本的杜梅利链球菌和半辐射链球菌感染。

The Lancefield serological group C Streptococcus sp. was isolated from cultured amberjack, Seriola dumerili Risso and yellowtail, Seriola quinqueradiata Temminck and Schlegel that had been immunized with Lactococcus garvieae commercial vaccines in Japan. The isolated bacteria were gram-positive cocci, auto-aggregated in saline, morphologically long chains in growth medium, catalase negative and α-haemolysis on blood agar. An almost complete gene sequence of the 16S rDNA of isolates (n=2) was determined and compared to that of bacterial strains in the data base. The isolates were identified to Streptococcus dysgalactiae based on the results of the 16S rDNA sequence, the bacteriological properties and the Lancefield serological grouping. The oligonucleotide primers designed with specifity for the 16S-23S rDNA intergenic spacer region of S. dysgalactiae amplified a gene from all the fish isolates as well as the type strains of α-haemolytic S. dysgalactiae subsp. dysgalactiae ATCC430738 and β-haemolytic S. dysgalactiae subsp. equisimilis ATCC35666, but not those of S. equiATCC33398, Lactococcus garvieaeATCC43921 and L. garvieae KG94 08. The severe lesion (a necrotic lesion of the caudal peduncle) observed on experimentally infected fish was similar to that seen on naturally infected fish. Further attention is required to distinguish the Lancefield group C Streptococcal infection from L. garvieae infection in S. dumerili and S. quinqueradiata in Japan.