Investigation of the High-order Effect of Rosmarinus officinalis, Salvia officinalis, and Thymus satureioides Essential Oils with Antibiotics on the Membrane Integrity of Salmonella typhi

AbstractAbstractThe development of pathogenic Salmonella typhi strains resistant to several classes of antibiotics has become a worldwide main health care concern. Combinations of plant essential oils and drugs provide a promising approach to overcome drug resistance. This study investigates the potential antibacterial activity of EOs extracted from Rosmarinus officinalis, Salvia officinalis, and Thymus satureioides, individually and in combination with conventional antibiotics against S. typhi. The screening of 27 antibiotics was performed by the disc diffusion method, and the minimum inhibitory concentration of the selected antibiotics and EOs were determined by the broth microdilution method. At the same time, the interactions between EO and drugs were assessed by determining the fractional inhibitory concentration (FIC) using the diagonal measurement of n-way drug interactions method. The mechanism of antibacterial effect against S. typhi was evaluated by measuring the product of lipid peroxidation (MDA), potassium leakage from the bacteria cells, and scanning electron microscopy. Antibacterial screening indicated that nine antibiotics induced strong antibacterial activity against S. typhi with MIC values ranging from 2 to 85 µg/mL. Moreover, the EOs revealed an interesting effect against S. typhi, with MIC values ranging between 0.068 and 1.25 mg/mL. The combination of R. officinalis, T. satureioides EOs, and piperacillin/tazobactam provided a strong and reproducible synergistic effect against S. typhi. This combination seemed to amplify the antibacterial activity of EOs and antibiotics against S. typhi by increasing their potency in disrupting bacterial cell membrane integrity. These findings suggest that this combination could be a promising option for controlling the emergence of multidrug-resistant S. typhi.Keywords: Essential oilsAntibioticsCombinationAntibacterial activityS. typhiMembrane integrity