Introduction: Oregano (Origanum vulgare L.) is an aromatic plant widely used as a condiment and in traditional medicine. Its essential oil, rich in carvacrol and thymol, stands out due to its recognized antimicrobial activity. The aim of this study was to evaluate the in vitro antimicrobial activity of oregano essential oil and to investigate its synergistic effect in combination with conventional antibiotics. Methodology: The essential oil, obtained by steam distillation of the leaves, was tested using the disk diffusion method. Standardized inocula of Staphylococcus aureus, Enterococcus faecalis, Klebsiella pneumoniae, and Pseudomonas aeruginosa were cultured on Müller–Hinton agar and tested with discs impregnated with 10 μL of the oil. Plates were incubated at 37 °C for 18 to 24 h, and inhibition zones were measured in triplicate. For synergy analysis, the oil was combined with amoxicillin, imipenem, tetracycline, ciprofloxacin, chloramphenicol, and gentamicin. Results: Oregano oil demonstrated a broad antimicrobial spectrum, with inhibition zones of 10.16 mm against P. aeruginosa, 21.85 mm against E. faecalis, 24.48 mm against K. pneumoniae, and 35.53 mm against S. aureus. It also exhibited a significant synergistic effect, enhancing the action of gentamicin against E. coli and S. aureus, as well as amoxicillin, imipenem, tetracycline, ciprofloxacin, and chloramphenicol against E. faecalis. Conclusions: The results confirm that oregano essential oil has remarkable potential as a natural antimicrobial agent, being promising both in isolated use and in combination with drugs, highlighting its relevance in addressing bacterial resistance.
Author Contributions
Conceptualization: C.A.P.R., I.C.R.S. and D.C.O.; methodology, software and validation and formal analysis: C.A.P.R., L.F.S.R., C.A.B., R.D.S., D.C.O. and I.C.R.S.; investigation and resource: C.A.P.R., L.F.S.R., C.A.B., R.D.S., D.O.F., A.S.S.M., T.D.D.C. and B.A.P.; data curation, C.A.P.R. and D.C.O.; writing—original draft preparation: D.C.O. and C.A.P.R.; writing—review and editing: D.C.O., I.C.R.S. and C.A.P.R.; visualization: C.A.P.R., C.A.B., R.D.S., D.O.F., A.S.S.M., T.D.D.C. and B.A.P.; supervision: I.C.R.S. and D.C.O.; project administration, D.C.O. and I.C.R.S.; funding acquisition: D.C.O. and I.C.R.S. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data presented in this study are available on request from the corresponding author. The data is not publicly available due to privacy interests.
Conflicts of Interest
The authors declare no conflicts of interest.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.