Comparative Evaluation of the Antimicrobial Activity of Crude Ethanolic Extracts of Local Medicinal Plants Against Escherichia coli and Salmonella spp

The increasing global threat of antimicrobial resistance (AMR) necessitates the exploration of alternative antibacterial agents derived from natural sources. This study evaluated the comparative antimicrobial activity of crude ethanolic extracts of turmeric (Curcuma longa), hibiscus (Hibiscus rosa-sinensis), croton (Croton spp.), ginger (Zingiber officinale), and oleander (Nerium oleander) against two Gram-negative pathogens, Escherichia coli and Salmonella spp. Antimicrobial efficacy was assessed using the agar disk diffusion method, and inhibition zones were statistically analyzed using independent samples t-tests and two-way ANOVA to determine strain-specific and pigment-specific effects. The overall grand mean inhibition zone across treatments was 13.45 mm, indicating moderate antibacterial activity. Salmonella spp. (14.35 mm) exhibited greater overall susceptibility than E. coli (12.54 mm). Turmeric demonstrated the highest antimicrobial activity (19.63 mm against Salmonella spp.; 16.66 mm against E. coli), followed by the tri colour croton variant. Red hibiscus showed balanced moderate activity against both strains, while oleander and ginger exhibited comparatively lower inhibition. Statistically significant strain-specific differences were observed only for pink hibiscus and red oleander extracts. Although most plant extracts demonstrated biologically relevant inhibition, variability and limited replication constrained statistical significance in several comparisons. The findings highlight the influence of phytochemical composition and bacterial susceptibility patterns on antimicrobial outcomes and support the continued investigation of plant-derived pigments, particularly turmeric and croton, as potential complementary agents in addressing antimicrobial resistance.