In vitro synergistic antibacterial activities of carvacrol, thymol and selected carvacrol-rich and carvacrol-deficient essential oil combinations

Abstract

The present study investigated the antibacterial activity of carvacrol, thymol, carvacrol-rich and carvacrol-deficient commercial essential oils (EOs) including Origanum onites, Thymbra spicata, Thymbra capitata, Eucalyptus radiata, and Mentha piperita and their combinations against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae. The minimum inhibitory concentrations (MICs) were 0.25 mg/mL for carvacrol, and 0.5 mg/mL for thymol against the bacteria tested. Carvacrol-rich EOs showed relatively higher antibacterial activity. Synergistic activity was observed in the combination of carvacrol with carvacrol-rich T. capitata EO against E. coli, with carvacrol-deficient M. piperita EO against S. aureus and E. faecalis, and in the combination of thymol-T. capitata EO against S. aureus. The synergism between carvacrol and carvacrol-rich EOs was not related to the total concentration of carvacrol. The synergistic combinations of carvacrol-T. capitata EO, carvacrol-M. piperita EO, and thymol-T. capitata EO are highlighted as a rational strategy for both food and cosmetic preservation and pharmaceutical applications.