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

The present study investigated the antibacterial activity of carvacrol, thymol, carvacrol-rich and carvacrol-deficient commercial essential oils (EOs) including <i>Origanum onites, Thymbra spicata, Thymbra capitata, Eucalyptus radiata</i>, and <i>Mentha piperita</i> and their combinations against <i>Enterococcus faecalis</i>, <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Klebsiella pneumoniae</i>. 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 <i>T. capitata</i> EO against <i>E. coli</i>, with carvacrol-deficient <i>M. piperita</i> EO against <i>S. aureus</i> and <i>E. faecalis</i>, and in the combination of thymol-<i>T. capitata</i> EO against <i>S. aureus.</i> The synergism between carvacrol and carvacrol-rich EOs was not related to the total concentration of carvacrol. The synergistic combinations of carvacrol-<i>T. capitata</i> EO, carvacrol-<i>M. piperita</i> EO, and thymol-<i>T. capitata</i> EO are highlighted as a rational strategy for both food and cosmetic preservation and pharmaceutical applications.