ICAR-Directorate of Coldwater Fisheries Research, Bhimtal, Uttarakhand, India.
ICAR-Indian Veterinary Research Institute, Bareilly, Uttar Pradesh, India.
Transbound Emerg Dis. 2018 Aug;65(4):1039-1048. doi: 10.1111/tbed.12843. Epub 2018 Feb 23.
"Warm water lactococcosis" in farm-reared rainbow trout, Oncorhynchus mykiss (Walbaum) in the northern Himalayan region of India, caused by bacterium Lactococcus garvieae is described in this study. Nine bacterial isolates were recovered from the organs of haemorrhagic septicaemia rainbow trout and were subjected to biochemical and molecular identification. Cell surface characteristics and virulence of the bacterial isolates are also described. All the nine bacterial isolates had homogenous biochemical characteristics and were Gram-positive, short chains forming (two to eight cells long), α-haemolytic, non-motile ovoid cocci. Partial 16S rDNA nucleotide sequence (~1,400 bp) of current isolates shared 99% identities with the 16S rDNA nucleotide sequence of L. garvieae R421, L. garvieae FMA395 and L. garvieae CAU:1730. The identity of the bacterial isolates was further confirmed by PCR amplification of L. garvieae-specific ~1,100 bp fragment. Transmission electron microscopy (TEM) of one representative isolate, L. garvieae RTCLI04, indicates that the isolated strain lacks thick outer capsule and is of KG+ (non-capsulates) phenotype. An intraperitoneal and intramuscular injection (2.6 × 10 CFU ml ) and also immersion in bacterial suspension @ of 2.6 × 10 CFU ml to healthy rainbow trout juveniles (body weight: 27.5 ± 3.7 g) with L. garvieae RTCLI04 caused 80%, 60% and 10% cumulative mortality in challenged fish, respectively, within 15 days post-infection. The haemorrhagic septicaemic disease was reproduced experimentally. Histopathological examination of organs of experimentally infected fish revealed extensive degenerative and inflammatory changes in eye, kidney, gill and liver. PCR amplification of several putative virulence genes such as haemolysins, adhesins, LPxTG-containing surface proteins and adhesins cluster confirms the virulence of our Indian L. garvieae isolates. To the best of our knowledge, we are reporting for the first time that L. garvieae is associated with fatal haemorrhagic septicaemia in farmed rainbow trout in India.
本研究描述了在印度北部喜马偕尔邦地区养殖的虹鳟鱼（Oncorhynchus mykiss (Walbaum)）中由乳球菌（Lactococcus garvieae）引起的“温水乳球菌病”。从出血性败血症虹鳟鱼的器官中分离出 9 株细菌，并进行了生化和分子鉴定。还描述了细菌分离株的细胞表面特征和毒力。所有 9 株细菌分离株的生化特征均相同，为革兰氏阳性，短链形成（2-8 个细胞长），α-溶血，非运动性卵形球菌。当前分离株的部分 16S rDNA 核苷酸序列（1400 bp）与 L. garvieae R421、L. garvieae FMA395 和 L. garvieae CAU:1730 的 16S rDNA 核苷酸序列具有 99%的同一性。细菌分离株的同一性通过 L. garvieae 特异性1100 bp 片段的 PCR 扩增进一步证实。代表菌株 L. garvieae RTCLI04 的透射电子显微镜（TEM）表明，该分离株缺乏厚的外胶囊，且为 KG+（无胶囊）表型。将浓度为 2.6×10 CFU ml-1 的细菌悬液腹腔内和肌肉内注射（2.6×10 CFU ml-1），以及浸泡在浓度为 2.6×10 CFU ml-1 的细菌悬液中，对体重为 27.5±3.7 g 的健康虹鳟幼鱼进行攻毒，在感染后 15 天内，分别导致 80%、60%和 10%的攻毒鱼累积死亡率。该出血性败血症疾病在实验中得到了重现。对实验感染鱼的器官进行组织病理学检查发现，眼睛、肾脏、鳃和肝脏均发生广泛的退行性和炎症性变化。对几种假定的毒力基因（如溶血素、粘附素、含 LPxTG 的表面蛋白和粘附素簇）的 PCR 扩增证实了我们的印度乳球菌分离株的毒力。据我们所知，这是首次报道乳球菌与印度养殖虹鳟鱼致命性出血性败血症有关。
