The aim of the present study was to investigate the chemical composition of the essential oil of the fruits of Eucalyptus globulus and to examine the potential application of the fruit oil against multidrug-resistant bacteria. GLC/MS analysis in the fruit oil showed that aromadendrene was the main compound followed by 1,8-cineole and globulol. The three most abundant components of the fruit oil were also tested individually against microorganisms. In addition, the synergistic effects of combinations of the major constituents (aromadendrene and 1,8-cineole) of the fruit oil were also investigated. All Gram-positive bacteria were susceptible to the fruit oil with different degrees of susceptibility as determined by microdilution method. The oil exerted a marked inhibition against multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) Enterococcus faecalis. The results indicated that aromadendrene might be responsible for the antimicrobial properties, whereas 1,8-cineole and globulol exhibited low activities. The checkerboard assay demonstrated that combinations of 1,8-cineole and aromadendrene reduce the MIC in most cases in an additive way, whereas the time-kill assay indicates a synergistic effect.
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Members of the genus Eucalyptus (Myrtaceae) originate from Australia but have been naturalized on most continents. Eucalyptus has been used in folk medicine throughout the world and the medicinal properties of these plants have been investigated. This family is an important source of essential oils with a wide range of biological activities such as antibacterial, antifungal, analgesic and anti-inflammatory properties (Ramezani et al. 2002; Sartorelli et al. 2007; Silva et al. 2003). Essential oils from Eucalyptus species are widely used in modern pharmaceutical, food and cosmetic industries (Lis-Balchin et al. 1998).
The essential oil of leaves of Eucalyptus globulus Labill. has been used all over the world as an antiseptic and for relieving symptoms of cough, cold, sore throat and other infections (Kumar et al. 2007; Van Wyk and Wink 2004). On the other hand, the essential oil of fruits of E. globulus has not been much explored yet. The chemical composition of the fruit oil has been studied (Cimanga et al. 2002; Ghalem and Mohamed 2008; Pereira et al. 2005), but antimicrobial properties have not been examined. Additionally, the contribution of the major components of the fruit oil to the antimicrobial activity has not been investigated. A previous study reported that the main compound of the fruit oil was 1,8-cineole (Basias and Saxena 1984), but also a different composition has been reported with aromadendrene as the main constituent (Pereira et al. 2005). In the present study we have reinvestigated the chemical composition of the fruit oil. Antibiotic-susceptible and antibiotic-resistant microorganisms were tested towards the fruit oil and the three major components (aromadendrene, 1,8-cineole, and globulol). Moreover, we have studied whether aromadendrene and 1,8-cineole produce additive or synergistic antibacterial effects, when applied in combination (as is the case of the oils).
Materials and methods
The fruits of E. globulus were kindly...
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