Purification and Evaluation of N-benzyl Cinnamamide from Red Seaweed Gracilaria fisheri as an Inhibitor of Vibrio harveyi AI-2 Quorum Sensing

Abstract

Previously, we reported that the ethanol extract from red seaweed <i>Gracilaria fisheri</i> effectively decreased biofilm formation of <i>Vibrio harveyi</i>. In this study, the anti-biofilm active compounds in the ethanol extract were isolated and their structures identified. The anti-biofilm fractionation assay for minimum inhibitory concentration (MIC) produced two fractions which possessed maximal inhibitory activities toward the biofilm formation of <i>V. harveyi</i> strains 1114 and BAA 1116. Following chromatographic separation of the bioactive fractions, two pure compounds were isolated, and their structures were elucidated using FTIR, NMR, and HR-TOF-MS. The compounds were <i>N</i>-benzyl cinnamamide and α-resorcylic acid. The in vitro activity assay demonstrated that both compounds inhibited the biofilm formation of <i>V. harveyi</i> and possessed the anti-quorum sensing activity by interfering with the bioluminescence of the bacteria. However, the <i>N</i>-benzyl cinnamamide was more potent than α-resorcylic acid with a 10-fold lesser MIC. The present study reveals the beneficial property of the <i>N</i>-benzyl cinnamamide from the ethanol extract as a lead anti-microbial drug against <i>V. harveyi</i>.