Chemical composition and antimicrobial activity of Plinia rivularis essential oil against multidrug-resistant bacteria

Introduction: The increasingly common occurrences of multidrug-resistant bacteria represent a global health threat and the discovery of new alternative remedies is necessary. The use of essential oils (EOs) in the treatment of many pathogenic bacteria is promising and several examples have already been highlighted regarding their inhibitory action. Among the botanical families, Myrtaceae stands out for presenting important species that supply bioactive products. Methods: In this work we investigate the chemical composition of Plinia rivularis (Myrtaceae) leaf EO and its antibacterial activity against resistant and non-resistant bacteria. The EO was obtained by two methods, hydrodistillation and steam distillation. Gas chromatography-flame ionization detector (GC-FID), gas chromatograph-mass spectrometry (GC-MS), nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR) were the techniques used in the EO chemical characterization. Results: The EOs were obtained with yields of 0.37 and 0.16% by hydrodistillation and steam distillation methods, respectively. The analyzes revealed the EOs chemical profile showing the compounds 2H-benzocyclohepten-2-one,3,4,4a,5,6,7,8,9-octahydro-4a-methyl (synonym: 4a-methyl-3,4,4a,5,6,7,8,9-octahydro-2Hbenzo[7]annulen-2-one), rosifoliol, beta-eudesmol and the diterpene kaurene as main constituents. Through preparative thin-layer chromatography (PTLC), it was possible to obtain the diterpene kaurene with a content of 91%, which was also characterized by NMR. The minimum inhibitory concentrations of EO against bacteria ranged from 0.56 to 2.25 mg.ml-1 and 2.25-36 mg.ml-1 for sensitive and resistant bacteria, respectively. Also, EO showed synergistic activity with amikacin and cefotaxime against carbapenem-resistant Pseudomonas aeruginosa (KPC). Conclusions: This is the first report on the chemical composition of P. rivularis EO. Comparison of extraction methods showed variation in yields and small changes in component content. The EO demonstrated activity against resistant and non-resistant bacteria. In addition, the synergistic effect of EO against resistant bacteria may be explored in future studies.