金乌贼幼体弧菌性坏死病的病原、组织病理特征和药物敏感性

对青岛市黄岛区人工繁育金乌贼(Sepia esculenta)苗种大规模坏死病进行了病原、组织病理、传播途径和防控药物研究。发病金乌贼幼体不摄食,生长缓慢,体色发黑;体表、肌肉、口腕、触腕及内脏团大面积溃烂,死亡率高达90%;组织病理学显示:患病金乌贼皮肤色素细胞崩解,肌丝断裂,鳃丝崩解,肝细胞大量坏死脱落,肠道微绒毛脱落;从患病金乌贼分离出3株优势菌(SE-A、SE-B和SE-C),人工感染实验表明,SE-B、SE-C对金乌贼半数致死量分别为3.98×10~6 CFU/mL和8.91×10~5 CFU/mL,有较强致病力,为该病的致病菌;根据细菌形态、生理生化和16S rDNA序列分析将SE-B和SE-C鉴定为溶藻弧菌(Vibrio alginolyticus)和塔氏弧菌(Vibrio tubiashii)。分析金乌贼幼体、育苗用水和生物饵料糠虾的病原菌来源、分布和优势度,发现致病菌主要由糠虾携带进入育苗系统。分析了2株致病菌的药物敏感性,SE-B对强力霉素和氟苯尼考等敏感,对链霉素、庆大霉素等耐药;SE-C对氟苯尼考和罗美沙星等敏感,对新霉素和克拉霉素等耐药。

Histopathological characteristics, pathogen, and drug sensitivity of vibrionic necrosis disease in the golden cuttlefish (Sepia esculenta)

The golden cuttlefish (Sepia esculenta) is a rising aquaculture species with high economic value in China. A disease with necrosis symptoms in golden cuttlefish larvae emerged in a hatchery in Huangdao District, Qingdao. In this study, the pathogen was isolated and identified, the histopathology was investigated, and its route of transmission and sensitivity to different antibiotics were tested. The symptoms included anorexia, slow growth, and a dark body. In addition, the skin, muscles, oral arm, tentacular arm, and the internal organs were extensively ulcerated, and the mortality reached as high as 90%. Histopathological analysis showed that the chromatophore and the gill filament structure were disintegrated, the myofilament was broken, a large number of hepatic lobule epithelial cells were necrotized, and the microvilli of intestinal epithelial cells were shed off. Three dominant bacteria (SE-A, SE-B, SE-C) were isolated from the diseased golden cuttlefish larvae. Artificial infection experiments illustrated that the strains of SE-B and SE-C were the causative pathogens with a median lethal dose of 3.98×10⁶ CFU/mL and 8.91×10⁵ CFU/mL, respectively. Based on morphological observations, and physiological, biochemical, and molecular analyses (16S rDNA), SE-B was identified as Vibrio alginolyticus and SE-C was identified as Vibrio tubiashii. The analysis of the transmission route demonstrated that the two pathogens present during golden cuttlefish breeding were mainly carried by Mysis species. The chemotherapeutant sensitivity tests illustrated that SE-B was sensitive to doxycycline and florfenicol, etc., while it was insensitive to streptomycin and gentamicin, etc. SE-C was sensitive to florfenicol and lomefloxacin, etc., while it was insensitive to neomycin and clarithromycin, etc.