Antimycobacterial Activity of Some Commercially Available Plant-Derived Essential Oils
Tuberculosis is part of a group of infectious diseases that together cause 90% of deaths worldwide . Mycobacterium tuberculosis, the causative agent of tuberculosis, infects approximately eight million new individuals per year and culminates in death every 10 seconds. Although the World Health Organization (WHO) has declared tuberculosis a global health emergency, its treatment lasts too long, infected patients have limited access to diagnosis, and multidrug-resistant strains of M. tuberculosis exist . Moreover, there has been a significant increase in the number of non-tuberculous mycobacteria (NTM), such as M. kansasii and M. avium, which may affect the lungs, lymph, skin, and joints and lead to serious sequelae when not treated . Thus, the search for new active molecules against mycobacteria is urgent. As part of our ongoing research on natural products as a source of new antimicrobial agents 4–7 , in this paper we investigate the antimycobacterial activity of 18 commercial plant-derived essential oils. We assessed the antimycobacterial activity of 18 essential oils against M. tuberculosis, M. avium, and M. kansasii by determining their minimum inhibitory concentrations (MICs, Table 1). Most of the essential oils were poorly active or inactive against M. tuberculosis, M. kansasii, and M. avium: MIC values ranged from 1000 to 2000 g mL–1 . However, the essential oils of Amyris balsamifera and Citrus limonum exhibited moderate activity against M. tuberculosis (MIC 500 g mL–1) and M. avium (MIC 500 g mL–1); the essential oils of Cynnamomum zeylanicum, Citrus paradise, Thymus vulgaris, Citrus limonum, Citrus sinensis, and Zingiber officinale also presented moderate activity against M. avium (MIC 500 g mL–1). Amyris balsamifera was the most active against M. kansasii (MIC 250 g mL–1). Papers have described the antimicrobial activity of Amyris balsamifera against Staphylococcus aureus  and Klebsiella pneumoniae , but this is the first time that the antimycobacterial activity of a commercially available essential oil of A balsamifera has been assessed. We used gas chromatography-mass spectrometry (GC-MS) to determine the chemical composition of Amyris balsamifera. Table 2 lists the 10 main compounds identified in this oil. The major constituents of Amyris balsamifera were the sesquiterpenes 7-epi-eudesmol (23.6%), agarospirol (14.0%), -eudesmol (12.3%), hedycaryol (10.9%), and drimenol (5.3%). The commercially available A. balsamifera essential oil from the Netherlands  and Germany  also contains -eudesmol, as well as the sesquiterpenes valerianol, elemol, and guaiol, which were not detected or were minor constituents in the present study. The 18 essential oils tested in this study were purchased from Body & Mind Beautiful Aromatherapy (Franca, SP, Brazil); the essential oils and their corresponding batch numbers are as follows: Amyris balsamifera (Rutaceae) (125), Boswellia carteri Birdw. (Burseraceae) (118), Cedrus atlantica (Endl.) Manetti ex Carriere (Pinaceae) (101), Cinnamomum zeylanicum Blume (Lauraceae) (099), Citrus bergamia Risso (Rutaceae) (114), Citrus limonum Risso (Rutaceae) (121), Citrus paradise Macfad. (Rutaceae) (145), Citrus sinensis (L.) Osbeck (Rutaceae) (100), Commiphora myrrha (T. Nees) Engl. (Burseraceae) (140), Copaifera officinalis (Jacq.) L. (Fabaceae) (128), Cupressus sempervirens L. (Cupressaceae) (126), Eucaliptus globulus Labill. (Myrtaceae) (125), Melaleuca auternifolia Cheel (Myrtaceae) (167), Pinus sylvestris L. (Pinaceae) (139), Pogostemom patchouli Pellet. (Lameaceae) (120), Salvia sclarea L. (Lamiaceae) (197), Thymus vulgaris L. (Lamiaceae) (137), and Zingiber officinale Roscoe (Zingiberaceae) (253).