Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Dis Aquat Organ. 2023 Sep 14;155:147-158. doi: 10.3354/dao03747.
Lactococcus petauri is an important emergent aquaculture pathogen in the USA. To better understand environmental conditions conducive to piscine lactococcosis and the susceptibility of fish species, laboratory-controlled challenges were used as models of infection. Rainbow trout Oncorhynchus mykiss maintained at 13 or 18°C were challenged by intracoelomic (ICe) injection with 101, 103 or 105 colony-forming units per fish (CFU fish-1) and monitored for 21 d. At 13°C, trout experienced mortalities of 7, 7 and 0%, and bacterial persistence of 0, 20 and 0% in survivors, respectively. When exposed to the same bacterial doses, trout maintained at 18°C experienced mortalities of 59, 84 and 91%, and bacterial persistence of 60, 66 and 0% in survivors, confirming a significant role of temperature in the pathogenesis of lactococcosis. Additionally, the susceptibility of rainbow trout, Chinook salmon Oncorhynchus tshawytscha, white sturgeon Acipenser transmontanus, Nile tilapia Oreochromis niloticus, and koi Cyprinus carpio to infection by L. petauri was compared using ICe challenges at 18°C. Trout and salmon experienced 96 and 56% cumulative mortality, respectively, and 17% of surviving salmon remained persistently infected. There were no mortalities in the other fish species, and no culturable bacteria recovered at the end of the challenge. However, when surviving fish were used in further cohabitation trials, naïve trout housed with previously exposed tilapia exhibited 6% mortality, demonstrating that non-salmonids can become sub-clinical carriers of this pathogen. The data obtained provide useful information regarding temperature-associated virulence, fish species susceptibility, and potential carrier transmission of L. petauri that can be used in the development of better management practices to protect against piscine lactococcosis.
海氏乳球菌是美国一种重要的水产养殖新兴病原体。为了更好地了解有利于鱼类乳球菌病的环境条件和鱼类物种的易感性，采用实验室控制的挑战来模拟感染。虹鳟鱼 Oncorhynchus mykiss 在 13°C 或 18°C 下通过腹腔内（ICe）注射每鱼 101、103 或 105 个菌落形成单位（CFU fish-1）进行挑战，并监测 21 天。在 13°C 下，虹鳟鱼的死亡率分别为 7%、7%和 0%，存活者中的细菌持续存在率分别为 0%、20%和 0%。当暴露于相同的细菌剂量时，在 18°C 下饲养的虹鳟鱼的死亡率分别为 59%、84%和 91%，存活者中的细菌持续存在率分别为 60%、66%和 0%，这证实了温度在乳球菌病发病机制中的重要作用。此外，还比较了虹鳟鱼、奇努克鲑鱼 Oncorhynchus tshawytscha、白鲟 Acipenser transmontanus、尼罗罗非鱼 Oreochromis niloticus 和锦鲤 Cyprinus carpio 对海氏乳球菌感染的敏感性，方法是在 18°C 下进行 ICe 挑战。虹鳟鱼和鲑鱼的累积死亡率分别为 96%和 56%，17%的存活鲑鱼仍持续感染。其他鱼类没有死亡，挑战结束时也没有可培养的细菌回收。然而，当幸存的鱼被用于进一步的同居试验时，与先前暴露的罗非鱼一起饲养的无经验虹鳟鱼表现出 6%的死亡率，表明非鲑鱼可以成为这种病原体的亚临床携带者。获得的数据提供了有关温度相关毒力、鱼类物种易感性和海氏乳球菌潜在携带者传播的有用信息，可用于制定更好的管理实践以预防鱼类乳球菌病。
