Antimicrobial Activity of Greek Native Essential Oils Against O157:H7 and Antibiotic Resistance Strains Harboring Plasmid, , -1 and Genes.

BACKGROUND/OBJECTIVES: The rapid emergence of antibiotic-resistant in food and clinical environments necessitates new, clean-label antimicrobials. This study assessed eight Greek native essential oils-oregano, thyme, dittany, rosemary, peppermint, lavender, cistus and helichrysum-for activity against six genetically and phenotypically diverse strains (reference, , , -1, and O157:H7). We aimed to identify oils with broad-spectrum efficacy and clarify the chemical constituents responsible.

METHODS

Disk-diffusion assays measured inhibition zones at dilutions from 50% to 1.56% (/). MIC and MBC values were determined by broth microdilution. GC-MS profiling identified dominant components, and Spearman rank-order correlations (ρ) linked composition to activity. Shapiro-Wilk tests (W = 0.706-0.913, ≤ 0.002) indicated non-normal data, so strain comparisons used Kruskal-Wallis one-way ANOVA with Dunn's post hoc and Bonferroni correction.

RESULTS

Oregano, thyme and dittany oils-rich in carvacrol and thymol-exhibited the strongest activity, with MIC/MBC ≤ 0.0625% (/) against all strains and inhibition zones > 25 mm at 50%. No strain-specific differences were detected (H = 0.30-3.85; = 0.998-0.571; p = 1.000). Spearman correlations confirmed that carvacrol and thymol content strongly predicted efficacy (ρ = 0.527-0.881, < 0.001). Oils dominated by non-phenolic terpenes (rosemary, peppermint, lavender, cistus, helichrysum) showed minimal or no activity.

CONCLUSIONS

Phenolic-rich EOs maintain potent, strain-independent antimicrobial effects-including against multidrug-resistant and O157:H7 strains-via a multi-target mode that overcomes classical resistance. Their low-dose efficacy and GRAS status support their use as clean-label food preservatives or adjuncts to antibiotics or bacteriophages to combat antimicrobial resistance.