Anti-Acinetobacter baumannii Activity of Volatile Oil Extracted from Medicinal Plants

Abstract

Acinetobacter baumannii is an important opportunistic pathogen of nosocomial infections. The improper use of antibiotics has result in emergence of multidrug resistant A. baumannii (MDR-A. baumannii). Therefore, the choice of available antibiotics is limited. The aim of the present study was to determine the antibacterial activity of volatile oils extracted from medicinal plants on the growth of MDR-A. baumannii. Volatile oils were extracted from 10 medicinal plants, including galangal, ginger, plai, lime, kaffir lime, sweet basil, tree basil, lemongrass, clove and cinnamon by water distillation method. All volatile oils were determined for their antibacterial activity against 30 strains of MDR-A. baumannii by agar disk diffusion and tea tree oil was used as positive control. The preliminary results demonstrated that 10 volatile oils possessed antibacterial activity against MDR-A. baumannii. Inhibition zones of cinnamon oil and clove oil were significantly larger than tea tree oil against MDR-A. baumannii (p<0.01). Moreover, inhibition zones of tree basil oil and tea tree oil showed no significant difference. Antibacterial activity assay by broth microdilution methods showed that volatile oils from cinnamon, clove, tree basil and kaffir lime possessed strong antibacterial activity and exhibited the MIC90 values of 0.25, 0.5, 1 and 1 mg/mL respectively and MBC90 values of 0.5, 1, 2 and 4 mg/mL, respectively. These results demonstrated that cinnamon oil showed the strongest antibacterial activity and thier major ingredients included cinnamaldehyde (75.89%), trans-cinnamyl acetate (7.07%), hydrocinnamaldehyde (2.39%) and 1,8-cineole (2.17%) when analyzed by Gas Chromatography-Mass Spectrometry. These results suggest that volatile oils extracted from cinnamon, clove, tree basil and kaffir lime may be used as alternative natural compounds to prevent and inhibit MDR-A. baumannii infection.