Chemical composition, antioxidant, antibacterial and anti-quorum sensing activities of Eucalyptus globulus and Eucalyptus radiata essential oils

Abstract

The interest in plant polyphenol antioxidants has increased remarkably over the last decade mostly because of their protective effects against different diseases, including cardiovascular, inflammatory and neurological diseases, cancer as well as for retarding aging. Many naturally occurring polyphenols found in plants and spices have also been shown to possess antimicrobial properties and could serve as a source of antimicrobial agents. Eucalyptus globulus and Eucalyptus radiata are well known species that provide essential oils. These oils are in great demand in the market, since they find a vast array of applications. The present study was performed to evaluate some bioactivities of the essential oils from E. globulus and E. radiata, namely their antioxidant, antibacterial and anti-quorum sensing properties. Moreover, its chemical composition was assessed and the potential synergistic activity with conventional antibiotics against Acinetobacter baumannii strains was also evaluated. The major component of the E. globulus oil was 1,8-cineole, also known as eucalyptol (63.81%), and in the E. radiata oil, the principal component was limonene (68.51%). It was possible to conclude that both eucalypt essential oils presented relevant radical scavenging properties and also had the capacity to inhibit the lipid peroxidation. The E. globulus oil antioxidant properties stand out when compared to the E. radiata oil. The E. radiata oil had a more pronounced antibacterial activity than E. globulus oil. The studied eucalypt essential oils can act as potential improving agents of antibiotics against A. baumannii, considering the synergic effect obtained between these oils and conventional antibiotics. Both eucalypt essential oils now studied can inhibit the quorum sensing phenomena, inhibiting quorum sensing-regulated violacein pigment production in bacteria without interfering with their growth.