Chemical Composition and Synergistic Antimicrobial Activity of Hypericum perforatum and Achillea millefolium Essential Oils Against Wound-Associated Microorganisms

Wound-associated infections persist as a major global health concern, particularly in the context of increasing antimicrobial resistance and reduced efficacy of conventional therapies. Essential oils (EOs) obtained from medicinal plants represent promising alternatives due to their antimicrobial and wound-healing properties. This study evaluated the chemical composition, antimicrobial activity, and interaction effects of Hypericum perforatum (HP) and Achillea millefolium (AM) EOs, tested individually and in fixed-ratio combinations. Chemical profiling by GC–MS revealed that HP EO is dominated by caryophyllene (20.74%) and β-thujone (18.47%), while AM EO is characterized by aromadendrene (19.12%), caryophyllene (12.97%), and chamazulene (10.13%). Antimicrobial activity was assessed against wound-associated microorganisms using MIC and MBC/MFC assays, and interactions were assessed by the fractional inhibitory concentration index (FICI) and heatmap analysis. The results displayed higher susceptibility of Gram-positive bacteria, particularly Staphylococcus epidermidis, with MIC values as low as 0.56 µL/mL in EO combinations. Synergistic effects were observed exclusively for S. epidermidis in mixtures enriched in HP EO (60:40 and 70:30; FICI = 0.34), while Gram-negative bacteria and Candida albicans exhibited predominantly indifferent responses. These findings indicate that optimized EO combinations may enhance antimicrobial efficacy and support their potential application in wound management.