Assessment of the antibacterial activity of Gnetum montanum extract against several aquatic pathogenic bacteria

Abstract

This study was conducted to evaluate the antibacterial activity of Gnetum montanum extract against selected aquatic pathogenic bacteria. The extract was prepared using a reflux extraction method with absolute ethanol. Antibacterial activity was assessed using the agar diffusion method and the broth microdilution method to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The 50% inhibitory concentration (IC₅₀) was calculated based on resazurin reduction. The tested bacteria included Aeromonas veronii, Aeromonas hydrophila, and Edwardsiella ictaluri, which are common pathogenic bacteria in freshwater fish. The results show that the extract inhibited Aeromonas veronii, Aeromonas hydrophila, and Edwardsiella ictaluri at concentrations of 5 – 10 mg/mL. The MIC values ranged from 0.5 to 2 mg/mL, with the strongest inhibition observed against E. ictaluri (MIC = 0.5 – 1 mg/mL). These findings suggest the potential application of Gnetum montanum extract as a natural antibacterial agent to replace antibiotics in aquaculture disease management.