GC-MS Profiling and Solvent-dependent in Vitro Antibacterial Activity of Zingiber officinale Roscoe Rhizome Extracts against Clinical Bacterial Isolates

Abstract

The global rise in antimicrobial resistance among clinically significant bacteria has intensified interest in plant-derived antibacterial agents. Zingiber officinale Roscoe (ginger) is a widely used medicinal spice whose rhizome extracts have long been associated with antimicrobial activity, but the influence of extraction solvent polarity on this activity against defined clinical isolates remains incompletely characterised. This study characterised the chemical profile of a crude Zingiber officinale rhizome extract and compared the antibacterial activity of five solvent extracts against four clinical isolates. The chemical composition of a crude ginger rhizome extract was profiled by gas chromatography-mass spectrometry (GC-MS). Antibacterial activity of five solvent extracts (aqueous, ethanolic, hexane, acetone, and ethyl acetate) was evaluated by agar well diffusion against four hospital-sourced clinical isolates (Klebsiella pneumoniae, Proteus mirabilis, Staphylococcus aureus, and Streptococcus pneumoniae) across a concentration gradient (12.5-100 mg/mL). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined for each solvent-isolate combination, and the MBC/MIC ratio was used to classify bactericidal versus bacteriostatic activity. GC-MS analysis of the crude extract resolved twenty-one reliably identified compounds, dominated by long-chain aliphatic hydrocarbons, fatty acids (n-hexadecanoic acid, 9-octadecenoic acid), and the triterpene squalene. All five solvent extracts produced concentration-dependent zones of inhibition against all isolates, with hexane and ethyl acetate extracts generally producing the largest zones at 100 mg/mL. In Table 5, the ethanolic extract had the lowest reported MIC for P. mirabilis (16.66 ± 0.95 mg/mL) and S. aureus (8.32 ± 0.67 mg/mL), whereas acetone was numerically lowest for K. pneumoniae (30.70 ± 2.90 mg/mL) and S. pneumoniae (8.13 ± 0.92 mg/mL). The reported antibacterial responses varied with extraction solvent and test isolate.