Antibacterial mechanism of Eugenia stipitata McVaugh essential oil and synergistic effect against Staphylococcus aureus

Abstract

The purpose of this study was to evaluate the antibacterial and antivirulence activities of an essential oil from E. stipitata (EsEO) leaves against Staphylococcus aureus as well as its mechanism of action. The determination of antibacterial activity was based on the MIC and MBC. The antibacterial mechanism was explored with growth curve, synergistic effect, antivirulence and cell membrane permeability assays. In addition, the antimicrobial activity in a model of S. aureus-infected Tenebrio mollitor larvae and the cytotoxicity on fibroblasts and macrophages were evaluated. The MIC and the MBC of EsEO were 128–512 μg/mL and 256–1024 μg/mL, respectively. The growth curve test showed that S. aureus was inhibited by EsEO. EsEO showed a synergistic effect with all investigated antibiotics and showed a high capacity to reduce hemolysis (78.18-92.48%) and staphyloxanthin (67.27-91.89%). The increase in the efflux of ions, proteins, and nucleic acids revealed that the integrity of the membrane had been affected. In addition, EsEO promoted protection in T. mollitor larvae infected with S. aureus. The essential oil from the leaves of E. stipitata did not present cytotoxic effects in machophages and fibroblast human cells and demonstrated antibacterial activity against S. aureus strains including multidrug resistant strains.