Comparative Assessment of the Antibacterial Efficacy of Zingiber officinale Extracts Against Multidrug Resistant Gram Negative Bacteria

A new class of therapeutic agents is needed to tackle multidrug-resistant (MDR) Gram-negative pathogens. This study has assessed the antibacterial activity of the aqueous, ethanolic and methanolic extracts of Zingiber officinale (ginger) against the clinical MDR strains of Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Phytochemical screening was carried out to identify the presence of alkaloids, flavonoids, phenolics and terpenoids in the plant species qualitatively. The antimicrobial potential was evaluated by disk diffusion tests with extracts of concentration 12.5 to 100 mg/mL and by broth microdilution method with extracts of concentration range 0.098 to 100 mg/mL and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) was determined. Six independent biological experiments were performed in all assays (n = 6). Among all the prepared extracts, the ethanolic extract exhibited the highest number of bioactive compounds and the largest inhibition zone (A. baumannii: 18.0 ± 0.6 mm; E. coli: 15.0 ± 0.8 mm; K. pneumoniae: 14.0 ± 0.7 mm; P. aeruginosa: 12.0 ± 0.7 mm), followed by methanolic, and the aqueous was least effective. These trends were further confirmed using microdilution endpoints, which showed that ethanolic extracts had the lowest MIC (6–10 mg/mL) and MBC (10–14 mg/mL) values for all of the target strains. A. baumannii was the most susceptible pathogen and P. aeruginosa showed the highest resistance. MBC/MIC ratios calculated consistently suggested bactericidal activity (1.4–1.67) for all the strains. The in vitro bactericidal activity of organic fractions of Z.