Fish disease pathogens: Antibacterial, anti-biofilm and anti- quorum sensing activities of selected medicinal plant extracts

Fish diseases such as kidney disease, dropsy and vibriosis pose serious challenges to the aquaculture industry, causing significant mortality. Antibacterial, anti-biofilm and anti-quorum sensing properties of selected plant extracts against reference strains and prevalent bacterial pathogens isolated from fishes were investigated. Acetone, ethanol and aqueous leaf extracts of Alchornea laxiflora (AL), Ficus exasperata (FE), Morinda lucida (ML), Jatropha gossypiifolia (JG), Ocimum gratissimum (OG) and Acalypha wilkesiana (AW) were screened against fish bacteria (five reference strains: Citrobacter freundii ATCC 8090; Aeromonas hydrophila ATCC 35654; Edwardsiella tarda ATCC 15947; Pseudomonas fluorescens ATCC 135225; Vibrio parahaemolyticus ATCC 17802; Vibrio alginolyticus ATCC 17749; and four clinical isolates: Lactococcus garviae B 970/23; Photobaclenum acumselae B44/16; Vibrio alginolyticus B789/2000). Acetone extracts of ML, JG and AW, the ethanol extract of AW, and aqueous extracts of AW and JG all had strong antibacterial activity, each showing excellent minimum inhibitory concentrations (MIC50% after 24 hours. Most plant extracts had selective minimum quorum sensing inhibition concentrations (MQSICs) against Chromobacterium violaceum . These findings highlight a promising alternative to conventional anti-infectives in the form of plant feed additives with potential use in controlling fish pathogens, particularly in terms of their efficacy against biofilm formation. Publication History Article published online: 05 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany