Antimicrobial activities of selected Thai medicinal plants bearing quinonoids

Abstract

Nine species of selected Thai medicinal plants bearing quinonoid compounds were investigated in vitro for their antimicrobial activities. The plant materials were sequentially extracted by maceration with petroleum ether and ethanol respectively. Thirteen tested pathogenic microorganisms included 5 gram positive bacteria, 6 gram negative bacteria and 2 fungi. The assays were performed by using agar well diffusion method for determination of inhibition zone and broth microdilution method for determination of minimum inhibitory concentrations (MIC) and minimum bactericidal concentration (MBC) or minimum fungicidal concentration (MFC) with two fold dilution. The results showed that most of the extracts and the quinone derivative compounds demonstrated a promising inhibitory effect against gram positive bacteria followed by fungi and gram negative bacteria. The ethanol extract of Xyris indica flowering heads and the petroleum ether extract of Eleutherine americana bulbs expressed broadest spectrum of antimicrobial activity. The petroleum ether extract of Rhinacanthus nasutus roots demonstrated lowest MIC and MBC on tested gram positive bacteria. The petroleum ether extract of Morinda citrifolia roots had promising antimicrobial potential against Candida albicans. This study revealed the antimicrobial potentials among selected Thai medicinal plants bearing quinonoid compounds which used as crude drugs in traditional Thai medicine.