Department of Anatomy, Faculty of Science, Mahidol University, Rama VI Road, Bangkok, Thailand.
National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency and Centex Shrimp, Chalermprakiat Building, Faculty of Science, Mahidol University, Rama VI Road, Bangkok, Thailand.
Fish Shellfish Immunol. 2019 May;88:91-101. doi: 10.1016/j.fsi.2019.01.058. Epub 2019 Feb 25.
Bacteria respond to host immunity for their proliferation and survival by cell-cell communications such as biofilm formation, bioluminescence, and secreting virulence factors. In the biofilm form, bacteria are more resistant to various antimicrobial treatments and withstand the host's immune system. The approaches of deciphering biofilm formation for treating bacterial infections are therefore highly desirable. Recently, we have reported that the ethanolic extract of the red seaweed Gracilaria fisheri (G. fisheri) enhanced immune activities and inhibited growth of the luminescent bacteria Vibrio harveyi in shrimp. We undertook the present research study in order to evaluate and compare the effectiveness of the ethanolic extract from G. fisheri and furanone, a known biofilm inhibitor, in inhibiting the formation of clinically important Vibrio biofilms. The results showed that sub-lethal concentrations of both the ethanolic extracts (5, 10 and 100 μg ml) and furanone (5 μM) inhibited biofilm formation by V. harveyi and Vibrio parahaemolyticus and also light production (luminescence) in V. harveyi. It is known that V. harveyi mediated light production via autoinducer AI-2 pathway, we further determined whether the inhibitory effect of the extract was involved the AI-2 signaling. The bioluminescence assay was conducted in an AI-2 deletion mutant V. harveyi. Supplementation of the AI-2 containing media with the extract or furanone impaired the light production in the mutant V. harveyi suggesting that the extract interfered AI-2 mediated light production similar to furanone. In vivo challenge study showed that the low concentrations (Sub MICs) of the ethanolic extract and furanone decreased bacterial adhesion and colonization in the surfaces of stomach lumen, down-regulated expression of a virulence factor, and protected shrimp against mortality from V. harveyi and V. parahaemolyticus infection. In conclusion, the present results suggest a potential application of the low concentrations of the ethanolic extract of G. fisheri as an efficient approach for treating biofilm-associated Vibrio diseases in aquacultures.
细菌通过细胞间通讯（如生物膜形成、生物发光和分泌毒力因子）来响应宿主免疫以增殖和存活。在生物膜形式下，细菌对各种抗菌处理更具抵抗力，并能抵抗宿主的免疫系统。因此，破译生物膜形成以治疗细菌感染的方法非常可取。最近，我们报道了红海藻石花菜（G. fisheri）的乙醇提取物增强了免疫活性并抑制了虾发光细菌哈维氏弧菌的生长。我们进行了本研究，以评估和比较 G. fisheri 的乙醇提取物和呋喃酮（一种已知的生物膜抑制剂）在抑制临床重要的弧菌生物膜形成方面的效果。结果表明，亚致死浓度的乙醇提取物（5、10 和 100μg/ml）和呋喃酮（5μM）均抑制了哈维氏弧菌和副溶血弧菌的生物膜形成，以及哈维氏弧菌的发光（生物发光）。已知哈维氏弧菌通过自诱导物 AI-2 途径介导发光，我们进一步确定提取物的抑制作用是否涉及 AI-2 信号。在 AI-2 缺失突变哈维氏弧菌中进行生物发光测定。用提取物或呋喃酮补充含有 AI-2 的培养基会损害突变哈维氏弧菌的发光，表明提取物干扰了 AI-2 介导的发光，类似于呋喃酮。体内攻毒研究表明，低浓度（亚最小抑菌浓度）的乙醇提取物和呋喃酮降低了胃腔表面细菌的黏附和定植，下调了一种毒力因子的表达，并保护虾免受哈维氏弧菌和副溶血弧菌感染的死亡率。总之，本研究结果表明，G. fisheri 的低浓度乙醇提取物可能作为治疗水产养殖中与生物膜相关的弧菌病的有效方法。
