Antibacterial Activity of Prenylated Flavonoids Isolated from Hop against Fish Pathogens Streptococcus iniae and Vibrio vulnificus

Reducing fish pathogenic bacteria outbreak is important as it results in economic losses in aquaculture. Antibiotics are an inevitable tool to control the pathogenic bacteria outbreak. However, the authorities are taking more regulations to prevent the emergence of drug-resistant strain development. Alternative materials to be employed for the purpose are needed from natural sources. In this research, we explored the antibacterial activity of natural products derived from hop against fish pathogenic strains Streptococcus iniae and Vibrio vulnificus . Antimicrobial activities of nine separates from hops were tested against S. iniae and V. vulnificus and identified. Xanthohumol ( 1 ) showed strongest antibacterial property against S. iniae . In addition, desmethylxanthohumol ( 4 ) and 8-prenylnaringenin ( 5 ) showed antibacterial against both of the tested pathogen strains. Antibacterial compounds were all prenylated flavonoids, and these might be used as index components for development of feed additives for fish in aquaculture.