Origanum vulgare oil: composition and in vitro activity of four Mediterranean aromatic plants

O. vulgare oil showed a composition concentrated primarily in carvacrol: 85.78% of the detected volatile profile. Simply put, its aroma and part of its experimental behavior depend on a mixture in which this molecule is largely predominant. However, this data does not define all oregano oils, because species, harvesting, and processing can profoundly alter the composition.

In antioxidant assays, oregano oil achieved 1.69 ± 0.07 mg/mL in reducing power and 9.2 ± 0.6 mg/mL in DPPH. These are chemical tests: they indicate the sample's ability to react in an artificial system, not the protection of a person's cells. In RAW264.7 cells, mouse macrophages used as a model for inflammatory response, the GI50 was 13.3 ± 0.5 µg/mL for the inhibition of nitric oxide production. The value signals activity in the model, but does not demonstrate an anti-inflammatory effect in the human body.

On a microbiological level, the oil showed the greatest antibacterial activity among the four samples examined. It inhibited the growth of all tested bacteria and achieved a bactericidal effect on Escherichia coli, Salmonella enterica, Yersinia enterocolitica, and Staphylococcus aureus between 0.08% and 0.63% by volume. Conversely, it did not show bactericidal activity, up to 2.5%, against Pseudomonas aeruginosa, Bacillus cereus, and Listeria monocytogenes. This confirms that the effect depends on the microorganism and the test conditions.

The value of this research is primarily comparative. It analyzes four oils obtained through a consistent procedure in the same experiment and links their chemical profile to multiple biological measurements. This helps to understand why it is incorrect to speak of essential oils from aromatic plants as if they were equivalent. In the oregano sample, the prevalence of carvacrol was associated with favorable results in various laboratory assays, while rosemary and sage showed different profiles and responses.

The work is also useful for potential technical applications, for example in research on food preservation or cosmetic formulations. However, activity against bacteria in a culture broth does not demonstrate efficacy in a complex food, on the skin, or in the gut. Similarly, a reduction of nitric oxide in isolated cells does not equate to a therapy for inflammatory conditions. The relevance is therefore preclinical and industrial, not clinical.

The research is based entirely on in vitro evidence, meaning tests conducted outside the body in chemical systems, cell cultures, and microorganisms. This type of study is suitable for generating hypotheses and comparing samples, but it cannot establish safety, effective dosage, or benefits for people. There is no data available regarding absorption, metabolism, tissue distribution, or drug interactions.

Furthermore, the effects depend on the specific product tested. An essential oil with 85.78% carvacrol does not automatically represent fresh oregano, dried oregano, or another batch of oil. The cancer cells used in the study are experimental models, and a reduction in their growth does not demonstrate anti-tumor activity in animals or patients. Finally, the oil did not act the same way against all bacteria. Therefore, these results do not authorize the use of the essential oil as a substitute for antimicrobial, anti-inflammatory, or oncological therapies.

A 2024 study on four commercial O. vulgare oils confirms the initial step of the chain: the oil's composition and its in vitro activity can be evaluated together, but they vary between samples. The experimental study used GC/MS, antioxidant assays, and antimicrobial tests on bacteria and fungi. It detected antimicrobial and antioxidant activity, with differences linked to the products' composition. This is a direct confirmation of the analytical approach used in the study by Spréa and colleagues, but it does not involve people nor does it demonstrate therapeutic efficacy [1].

A second experimental study compared eight samples from two oregano genotypes, one rich in carvacrol and one rich in thymol. The supported premise is that the volatile profile may be associated with different effects against microorganisms and in cellular intestinal models. The oils showed antimicrobial activity even in a food matrix test; however, no relevant anti-inflammatory effects emerged in Caco-2 cells. The confirmation of antimicrobial activity is therefore moderate, while that of the anti-inflammatory action remains weaker and dependent on the model [2].

A study on O. vulgare subsp. hirtum oil, HepG2 liver carcinoma cells, and human embryonic kidney HEK293 cells supports the cytotoxicity data observed by Spréa and colleagues. The model included cell cultures and bacteria, not animals or patients; the oil and some of its components reduced the viability of HepG2 cells and showed antibacterial activity. The relationship with the main research is direct at the preclinical level, but the substantial limitation is that selectivity in culture does not equate to an oncological treatment [3].

Research on seven populations of O. vulgare, grown under similar conditions and observed over two years, shows why the sample used by Spréa and colleagues cannot represent the entire species. The essential oil content varied from 0.12% to 1.76% and carvacrol from 0.3% to 46.8%; four chemotypes were identified, meaning groups of the same species with different chemical profiles. This does not refute the value of the carvacrol-rich sample, but it limits the ability to generalize these findings to other oreganos [4].

A further study on O. vulgare subsp. glandulosum found variations between the vegetative stage and flowering. Carvacrol levels fluctuated from 61.08% to 83.37%, oil yield changed, and the minimum inhibitory concentrations against five sensitive bacteria ranged between 125 and 600 µg/mL. The result supports the dependence of activity on the plant material and the harvesting phase. No directly conflicting evidence of sufficient relevance was identified; this does not prove the absence of contrary results [5].