Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Stoneville, Mississippi, USA.
Department of Fish Diseases and Management, Faculty of Veterinary Medicine, Beni-Suef University, Beni-Suef, Egypt.
J Fish Dis. 2022 Dec;45(12):1817-1829. doi: 10.1111/jfd.13703. Epub 2022 Aug 21.
Catfish farming is the largest aquaculture industry in the United States and an important economic driver in several southeastern states. Edwardsiella piscicida is a Gram-negative pathogen associated with significant losses in catfish aquaculture. Several Gram-negative bacteria use the BasS/BasR two-component system (TCS) to adapt to environmental changes and the host immune system. Currently, the role of BasS/BasR system in E. piscicida virulence has not been characterized. In the present study, two mutants were constructed by deleting the basS and basR genes in E. piscicida strain C07-087. Both mutant strains were characterized for virulence and immune protection in catfish hosts. The EpΔbasS and EpΔbasR mutants were more sensitive to acidic environments and produced significantly less biofilm than the wild-type. In vivo studies in channel catfish (Ictalurus punctatus) revealed that both EpΔbasS and EpΔbasR were significantly attenuated compared with the parental wild-type (3.57% and 4.17% vs. 49.16% mortalities). Moreover, there was significant protection, 95.2% and 92.3% relative percent survival (RPS), in channel catfish vaccinated with EpΔbasS and EpΔbasR against E. piscicida infection. Protection in channel catfish was associated with a significantly higher level of antibodies and upregulation of immune-related genes (IgM, IL-8 and CD8-α) in channel catfish vaccinated with EpΔbasS and EpΔbasR strains compared with non-vaccinated fish. Hybrid catfish (channel catfish ♀ × blue catfish ♂) challenges demonstrated long-term protection against subsequent challenges with E. piscicida and E. ictaluri. Our findings demonstrate BasS and BasR contribute to acid tolerance and biofilm formation, which may facilitate E. piscicida survival in harsh environments. Further, our results show that EpΔbasS and EpΔbasR mutants were safe and protective in channel catfish fingerlings, although their virulence and efficacy in hybrid catfish warrant further investigation. These data provide information regarding an important mechanism of E. piscicida virulence, and it suggests EpΔbasS and EpΔbasR strains have potential as vaccines against this emergent catfish pathogen.
鲶鱼养殖是美国最大的水产养殖产业，也是东南部几个州的重要经济驱动力。爱德华氏菌是一种与鲶鱼水产养殖中大量损失相关的革兰氏阴性病原体。几种革兰氏阴性细菌使用 BasS/BasR 双组分系统 (TCS) 来适应环境变化和宿主免疫系统。目前，BasS/BasR 系统在 E. 鱼爱德华氏菌毒力中的作用尚未得到表征。在本研究中，通过删除 E. 鱼爱德华氏菌菌株 C07-087 中的 basS 和 basR 基因构建了两个突变体。对鲶鱼宿主的毒力和免疫保护作用进行了特征分析。EpΔbasS 和 EpΔbasR 突变株对酸性环境更敏感，生物膜生成量明显低于野生型。在斑点叉尾鮰（Ictalurus punctatus）体内研究表明，与亲本野生型相比，EpΔbasS 和 EpΔbasR 突变株的毒力显著减弱（分别为 3.57%和 4.17%死亡率）。此外，用 EpΔbasS 和 EpΔbasR 接种的斑点叉尾鮰对爱德华氏菌感染的保护率分别为 95.2%和 92.3%，相对存活率（RPS）显著提高。与未接种鱼相比，用 EpΔbasS 和 EpΔbasR 接种的斑点叉尾鮰的抗体水平显著升高，免疫相关基因（IgM、IL-8 和 CD8-α）的表达水平上调。杂交鲶（斑点叉尾鮰♀×蓝鲶♂）的挑战表明，对爱德华氏菌和鮰爱德华氏菌的后续挑战具有长期保护作用。我们的研究结果表明 BasS 和 BasR 有助于酸耐受和生物膜形成，这可能有助于爱德华氏菌在恶劣环境中生存。此外，我们的结果表明，EpΔbasS 和 EpΔbasR 突变体在斑点叉尾鮰鱼苗中是安全和有保护作用的，尽管它们在杂交鲶鱼中的毒力和功效需要进一步研究。这些数据提供了爱德华氏菌毒力的一个重要机制的信息，并表明 EpΔbasS 和 EpΔbasR 菌株有可能作为这种新兴的鲶鱼病原体的疫苗。
