Antibacterial Essential Oils as Adjuvants to Inhibit Antibiotic Resistance in Multidrug-resistant Bacteria

In order to contribute to the fight against the antibiotic resistance crisis, we used a dual-activity prospection strategy for natural product mixtures with antibiotic resistance modulating and antibacterial activities in the essential oils (EOs) of Artemisia ludoviciana, Lippia graveolens, and Cosmos bipinnatus against multidrug-resistant strains of Pseudomonas aeruginosa HIM-MR01, Staphylococcus aureus HIM-MR02, Enterococcus faecalis HIM-MR05, and Salmonella typhi HIM-MR06. The three EOs exerted antibacterial activity on the bacterial strains with minimum inhibitory concentrations (MICs) ranging from 0.1735 to 65.6263 µg/mL. When combined with antibiotics, the L. graveolens EO showed the highest resistance modulation for vancomycin (VA), nalidixic acid (NA), and chloramphenicol against S. aureus (MIC: 0.0347 µg/mL), E. faecalis (MIC: 0.0832 µg/mL), and P. aeruginosa (MIC: 0.0694 µg/mL). For the A. ludoviciana EO, resistance modulation was based on S. aureus-VA (MIC: 0.6525 µg/mL) and E. faecalis-NA (MIC: 0.3262 µg/mL). Thereby, C. bipinnatus EO did not show significant antibiotic resistance modulating activity. In conclusion, L. graveolens and A. ludoviciana EOs showed antibacterial activity and the greatest potential in inhibiting bacterial resistance to antibiotics. The dual activity of these EOs makes them a promising adjuvant in the treatment of diseases caused by multidrug-resistant pathogenic bacteria.