Antimicrobial Screening of Thirteen Aqueous Plant Extracts against Selected Pathogenic Fish Bacteria

Abstract

Plants produce bioactive compounds with anti-bacterial properties, making them a viable alternative to antibiotic use in aquatic disease management. However, studies on using aqueous plant extracts in aquaculture as biocontrol agents are still limited. In this study, the anti-bacterial properties of 13 plant extracts, prepared using green and environmentally friendly hot water extraction techniques, were screened against three pathogenic fish bacteria, namely Aeromonas hydrophila, Streptococcus agalactiae, and Staphylococcus xylosus. Interestingly, the findings revealed that out of 13 extracts, only three plants, Jacaranda filicifolia, Tamarindus indica, and Samanae saman, demonstrated significantly high potency (as low as 50 mg) in inhibiting these bacteria, as determined by the broth dilution method. By means of the well diffusion method, these three plant extracts exhibited considerably high antimicrobial activity, with a strong inhibition (9-15mm) against all three fish pathogens except S. saman with little inhibition on A. hydrophila (2mm). The phytochemical test in the selected plants revealed that the extracts of J. filicifolia had a high concentration of alkaloids, tannin, and triterpenes. The gas chromatography and mass spectrometry study (GC-MS) indicated a high concentration of hydroquinone (43.16%). In comparison, the HPLC results of J. filicifolia indicated the presence of a good content of sucrose (15.17%), galactose (13.46%), glucose (33.06%), and fructose oligosaccharides (38.31%). In general, J. filicifolia could be used as an alternative antimicrobial agent for disease management in aquaculture.