Antimicrobial Activity of a Carvacrol-rich Thymus maroccanus Ball. Essential Oil: Whole-oil Superiority over its Major Constituent

Abstract

This study characterized Thymus maroccanus essential oil (TMEO) and compared its antimicrobial activity with carvacrol and their combination. The TMEO was obtained by microwave-assisted hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC–MS), revealing a carvacrol-dominant profile (71.04%) with 11 compounds representing 98.52% of the volatile fraction. Antimicrobial activity was assessed against Gram-positive and Gram-negative bacteria and clinical Candida isolates using disc diffusion minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) assays. TMEO showed low MIC values and bactericidal activity against Staphylococcus aureus and Micrococcus luteus (MBC/MIC ≤ 2), while Escherichia coli was less susceptible. Notably, TMEO consistently outperformed carvacrol alone, indicating that the activity of the whole oil cannot be explained by its major component only. A 1:1 (v/v) TMEO–carvacrol combination further improved antimicrobial activity against several strains, particularly Gram-positive bacteria and Candida albicans. However, in the absence of interaction assays, this effect is interpreted as enhanced combined activity rather than confirmed synergy. The observed differences in susceptibility are consistent with known structural and physiological variation among microorganisms. In conclusion, T. maroccanus was found to be a carvacrol-rich chemotype with promising antimicrobial activity, warranting further mechanistic, safety, and formulation studies for practical  applications.