Inhibitory Effects of Plant Extracts on the Growth of Five Pathogenic Bacteria

The objective of this study was to investigate the antimicrobial activities of essential oils (EO) and spice extracts of the plants popularly used in Thai cuisines, namely galangal (Alpinia galanga (Linn.) Stuntz.), finger root (Boesenbergia pandurata Roxb.), lemongrass (Cymbopogon citrates) and torch ginger (Etlingera elatior). The plant extracts were prepared using steam distillation, supercritical fluid extraction (SFE) and conventional Soxhlet extraction techniques. Results demonstrated that galangal extracted by SFE and Soxhlet extraction techniques showed stronger antimicrobial activity against Staphylococcus aureus and Listeria monocytogenes than those of finger root, lemongrass and torch ginger, respectively. Escherichia coli and Salmonella typhimurium, as well as Gram-positive pathogenic bacteria, such as S. aureus and L. monocytogenes, were sensitive to lemongrass EO.