Combining the principles of Nature with the application of modern technology, it now can be shown how Oregano inhibits common foodborne microorganisms. The ability of culinary herbs to retard food spoilage has been known since ancient times. Recent studies have focused on the ability of essential oils, leaves and active principles of aromatic plants to inhibit a wide variety of foodborne microorganisms with an emphasis on food safety. In this context, oregano (Oreganum vulgare) is especially interesting. This perennial, pungent herb possesses strongly aromatic leaves, and it has been classified as a GRAS (Generally Recognized as Safe) food additive. Oregano was found to possess stronger antimicrobial properties than onion, ginger, black pepper, cumin, rosemary, mustard, basil, coriander and sage when tested against a variety of common molds and fungi.

The antimicrobial activity of herbs is concentrated in lipid extracts, known as essential aromatic oils. The antifungal effects of essential oils, including oregano, cloves, garlic, onion, savory and thyme were first reported in 1956. These observations were extended by Belaiche, who described the antimicrobial effects of essential oils of 44 different herbs and spices using an agar diffusion method. That study indicated the oil of oregano effectively inhibited the growth of Candida albicans, as well as several undesirable bacteria. More recently, 32 essential oils were screened for their ability to inhibit food spoilage and industrial yeasts. Oregano was found to be one of the strongest inhibitors.

Oil of oregano contains a variety of terpenoids and phenolic compounds. The phenolic terpenoid, carvacrol, is a major constituent of this oil. Several reports had shown that carvacrol inhibited C. albicans and Pseudomonas aeruginosa and foodborne organisms. We demonstrated that carvacrol inhibited C. albicans as effectively as oil of oregano. Analysis demonstrated that our oil of oregano contained approximately 60% carvacrol and we concluded that the anti-Candida properties of this essential oil are likely due to its content of carvacrol. Other studies demonstrated sensitivity of Staphylococcus aureus, Pseudomonas spp, Proteus mirabilis, Klebsiella pneumonia and group B streptococcus, E coli, Aerobacter aerogluess, and Bacillus subtilis to oregano. Therefore, the data indicate that oil of oregano exhibits a broad spectrum antimicrobial activity. Although the mechanism of action of essential oils is unknown, it has been suggested that essential oils can bind to cell membranes and interfere with microbial membrane function.

Microbiol 1999 Oct;65(10):4606-10

Mechanisms of action of carvacrol on the food-borne pathogen Bacillus cereus.
Ultee A, Kets EP, Smid EJ

Agrotechnological Research Institute, 6700 AA Wageningen, The Netherlands. A.Ultee@ato.dlo.nl

Carvacrol, a naturally occurring compound mainly present in the essential oil fraction of oregano and thyme, was studied for its effect on bioenergetic parameters of vegetative cells of the food-borne pathogen Bacillus cereus. Incubation for 30 min in the presence of 1 to 3 mM carvacrol reduced the viable cell numbers exponentially. Carvacrol (2 mM) significantly depleted the intracellular ATP pool to values close to 0 within 7 min. No proportional increase of the extracellular ATP pool was observed. Depletion of the internal ATP pool was associated with a change of the membrane potential (Deltapsi). At concentrations of 0.01 mM carvacrol and above, a significant reduction of Deltapsi was observed, leading to full dissipation of Deltapsi at concentrations of 0.15 mM and higher. Finally, an increase of the permeability of the cytoplasmic membrane for protons and potassium ions was observed (at 0.25 and 1 mM carvacrol, respectively). From this study, it could be concluded that carvacrol interacts with the membranes of B. cereus by changing its permeability for cations like H(+) and K(+). The dissipation of ion gradients leads to impairment of essential processes in the cell and finally to cell death.

Phytother Res 2000 May;14(3):213-4

Inhibition of enteric parasites by emulsified oil of oregano in vivo.
Force M, Sparks WS, Ronzio RA

Health Explorations Trust, Scottsdale, AZ, USA (M.F.) and Biotics Research Corporation, P.O. Box 36888, Houston, Texas 77236, USA.

Oil of Mediterranean oregano Oreganum vulgare was orally administered to 14 adult patients whose stools tested positive for enteric parasites, Blastocystis hominis, Entamoeba hartmanni and Endolimax nana. After 6 weeks of supplementation with 600 mg emulsified oil of oregano daily, there was complete disappearance of Entamoeba hartmanni (four cases), Endolimax nana (one case), and Blastocystis hominis in eight cases. Also, Blastocystis hominis scores declined in three additional cases. Gastrointestinal symptoms improved in seven of the 11 patients who had tested positive for Blastocystis hominis.