Antibacterial Activity of Alpinia galanga Ethanol Extract against Escherichia coli, Shigella dysenteriae, and Vibrio cholerae

Enteric infections caused by Gram-negative bacteria encourage the investigation of plant-derived antibacterial agents. This study evaluated the antibacterial activity of ethanolic galangal (Alpinia galanga) rhizome extract against Escherichia coli, Shigella dysenteriae, and Vibrio cholerae. The extract was prepared by maceration using 96% ethanol and tested using the disk diffusion method at concentrations of 5%, 10%, and 15% (w/v), with ciprofloxacin and distilled water as positive and negative controls, respectively. Four technical replicates were performed for each treatment. The highest mean inhibition-zone diameters among the extract treatments were observed at 15%, reaching 10.05 mm for E. coli, 9.58 mm for S. dysenteriae, and 11.68 mm for V. cholerae. One-way ANOVA across all five treatment groups indicated differences in inhibition-zone diameters for all tested bacteria (p < 0.001). However, separate analyses of extract concentrations identified a difference only for V. cholerae (ANOVA p = 0.0036; Welch ANOVA p = 0.0120), whereas no significant differences were detected for E. coli or S. dysenteriae. The results demonstrate observable antibacterial inhibition by galangal rhizome extract under the experimental conditions, although the concentration–response pattern was inconsistent. As the measurements were technical replicates derived from the same bacterial suspension, statistical findings should be interpreted as exploratory. Further investigations using independent biological replicates, standardized disk loading, and dilution-based assays are required to confirm the antibacterial potential of the extract.