Mexican Oregano Essential Oil Research Articles

Effect of pH and Mexican Oregano (Lippia berlandieri Schauer) Essential Oil Added to Carboxymethyl Cellulose and Starch Edible Films on Listeria monocytogenes and Staphylococcus aureus

The aim of this work was to evaluate the effect of pH and Mexican oregano essential oil (MOEO) added to carboxymethyl cellulose (CMC) and starch (S) edible films on Listeria monocytogenes and Staphylococcus aureus. CMC and S edible films were formulated with different concentrations (0%, 0.25%, 0.50%, 0.75%, and 1%) of MOEO at different pH (5, 6, or 7). Antimicrobial assay was performed. Inhibition curves were fitted to the Fermi model. Significant differences (p<0.05) were found in tc (time to reduce 50% of microbial population) and a (slope of the curve around tc), being lower at acidic pH. For L. monocytogenes, CMC films exhibited a higher antimicrobial effectiveness (0.50% of MOEO) compared to S films which need a higher concentration of MOEO (0.75%). S. aureus was inhibited with CMC films at 0.50% MOEO and pH 5 and 6. Microbial modeling has allowed estimating key intrinsic factors as pH and MOEO concentration with the synergistic effect against two important food-borne pathogens.

β-Cyclodextrin inclusion complexes containing clove (Eugenia caryophyllata) and Mexican oregano (Lippia berlandieri) essential oils: Preparation, physicochemical and antimicrobial characterization

Abstract Mexican oregano and clove essential oils are widely used as antimicrobial, insecticidal, antifungal and antioxidant compounds. To reduce their volatility and their hydrophobicity, they were encapsulated in β-cyclodextrin (β-CD) complexes by co-precipitation method, and the physicochemical and microbiological properties of these inclusion complexes were characterized. Different essential oil (EO) to β-CD weight ratios were tested (4:96, 8:92, 12:88, and 16:84 w/w) and encapsulation efficiency and rate were determined. GC–MS and GC-FID analysis were also performed to determine the main oil constituents, which were eugenol and carvacrol in clove and Mexican oregano essential oils respectively and to quantify their ratio in inclusion complexes. 1 H NMR spectroscopy confirmed essential oil inclusion. The 4:96 ratio (clove essential oil:β-CD) gave the highest eugenol content and greatest microencapsulation efficiency; and the 8:92 and 12:88 ratios (Mexican oregano essential oil: β-CD) the highest carvacrol content. Complexes antimicrobial activity was tested against two food-related microorganisms: Listeria monocytogenes ATCC 19114 and Escherichia coli ATCC 25922 by means of agar disk diffusion assay. The results demonstrated the inclusion of the majority of biologically active clove and Mexican oregano essential oil molecules, providing increased stability by reducing their volatility and preserving their biological properties.

Effect of Nanoemulsified and Microencapsulated Mexican Oregano (Lippia graveolens Kunth) Essential Oil Coatings on Quality of Fresh Pork Meat.

Fresh meat is a highly perishable food. This work aimed to evaluate the influence of Mexican oregano (Lippia graveolens Kunth) incorporated into active coatings (ACs) spread on fresh pork meat as free (FEO), nanoemulsified (NEO), and microencapsulated (MEO) essential oil (EO), on its microbiological, physicochemical and sensory properties during 15 d at 4 ± 1 °C. Thymol and γ-terpinene were identified in the EO. In vitro effect of 2.85 mg EO/cm2 was tested against Brochothrix thermosphacta, Micrococcus luteus, Lactobacillus plantarum, Pseudomonas fragi, and Salmonella Infantis. FEO antioxidant capacity (DPPH assay) was significantly higher than that of thymol, NEO and MEO (93.53%, 89.92%, 77.79%, and 78.50% inhibition, respectively), and similar to BHA (96.03%) and gallic acid (95.57%). FEO, NEO, and MEO ACs on meat caused growth inhibition of lactic acid bacteria (5 log population reduction) and Pseudomonas spp. (4 log reduction), whereas ≤1.5 log population reduction was observed for B. thermosphacta and Salmonella Infantis. Meat microbiota was more efficiently controlled by MEO than by FEO or NEO. ACs delayed lipid and oxymyoglobin oxidation of fresh pork meat. After 15 d of cold storage meat added with EO coatings was desirable for panelists, whereas untreated (UT) samples were undesirable. Active coatings are a significant alternative method for fresh meat preservation.

Antifungal Activity of Microcapsulated Clove (Eugenia caryophyllata) and Mexican Oregano (Lippia berlandieri) Essential Oils against Fusarium oxysporum

The aim of the present study was to determine the antifungal activity of microcapsules of essential oil of clove (Eugenia caryophyllata) and Mexican oregano (Lippia berlandieri) against Fusarium oxysporum. Different essential oil to β-cyclodextrin weight ratios were tested, (4:96, 8:92, 12:88 and 16:84 w/w) and encapsulation efficiency same as rate, were determined. GC-MS and GC-FID analysis were also performed to determine. The main oil constituents, which were eugenol and carvacrol in clove and Mexican oregano essential oils respectively and to quantify their ratio in microcapsules. The oxford cup method was used to determine the antifungal inhibitory activity of essentials oils and microcapsules of essential oils. The results showed that the 4:96 ratio (clove essential oil:β-cyclodextrin) gave the highest Eugenol content and the greatest microencapsulation efficiency; and the 8:92 and 12:88 ratios (Mexican oregano essential oil: β-cyclodextrin) gave the highest carvacrol content. The essential oil of cloves and Mexican oregano showed the greatest inhibition values against Fusarium at the beginning of the tests; however, after 8 days of analysis, the microcapsules containing essential oil of clove were the most effective ones. Putting everything together, our findings indicate that the antifungal activity of the β-cyclodextrin-essential oils capsules, show great promise for the extensive control of Fusarium oxysporum.

Effectiveness of Mexican oregano essential oil from the Dominican Republic (Lippia graveolens) against maize pests (Sitophilus zeamais and Fusarium verticillioides)

The insecticidal and antifungal properties of Mexican oregano (Lippia graveolens) essential oil from the Dominican Republic were investigated under laboratory conditions against two main pests of stored grains: Sitophilus zeamais and Fusarium verticillioides. Although oregano essential oil at 600 ?l/l air did not result in a significant mortality of S. zeamais after 24 hours of exposure by fumigation, this essential oil was a powerful acetylcholinesterase (AChE) inhibitor in vitro. One of the main components of oregano essential oil, p-cymene, presented fumigant toxicity and AChE inhibition activity against the maize weevil. The L. graveolens essential oil antifungal activity against F. verticillioides was evaluated at 50, 100 and 200 ?l/l, and it was found that growth parameters were affected by the presence of oregano essential oil in the media, whereas FB1 production was not inhibited. The results demonstrate that oregano essential oil and p-cymene can be used as alternatives to synthetic pesticides against F. verticillioides and S. zeamais, respectively.

Stability of Mexican Oregano Essential Oil Double Emulsions Obtained by Ultrasound Formulated With Whey Protein Concentrate and Tween 80

Water-in-oil-in-water (W/O/W) emulsions have a great potential use for food applications because they can protect sensitive compounds, such as essential oils. The aim of this study was to determine the effect of ultrasonic homogenization parameters: intensity (42 or 54 µm) and time (5 or 7.5 min); and formulation: oil phase proportion (20 or 30%) and emulsifier concentration (0 or 0.3%); on the physical and stability properties of Mexican oregano essential oil (OEO) in double emulsions. The emulsions were made in a two-step process, primary emulsions (W/O) containing OEO in the oil phase and ascorbic acid solution in the water phase, were stabilized with lecithin; while secondary emulsions were stabilized with 6% (w/w) of whey protein concentrate (WPC) and with or without Tween 80 (T80). Creaming, viscosity and droplet size distribution were measured to determine the stability of the W/O/W emulsions; as well as other physical properties like density and pH. The prepared W/O/W emulsions had droplet sizes between 2.89(±0.589) µm and 4.123(±0.964) µm. The most stable emulsions, with no creaming developed after 25 days of storage, were the ones formulated with WPC with T80, and additionally, 30% of the primary emulsion. Besides, higher intensity and longer time of ultrasonic homogenization conditions applied enhances W/O/W stability. Empirical models were developed for viscosity and creaming properties of W/O/W emulsions, with 99.7% of correlation coefficients, finding optimum values for specific homogenization conditions and formulation. Further studies are suggested to evaluate OEO in W/O/W emulsions as controlled release systems in food.

Antimicrobial Activity of Individual and Combined Essential Oils against Foodborne Pathogenic Bacteria

The antimicrobial activities of essential oils from Mexican oregano (Lippia berlandieri Schauer), mustard (Brassica nigra), and thyme (Thymus vulgaris) were evaluated alone and in binary combinations against Listeria monocytogenes, Staphylococcus aureus, or Salmonella Enteritidis. Chemical compositions of the essential oils were analyzed by gas chromatography-mass spectrometry. The MICs of the evaluated essential oils ranged from 0.05 to 0.50% (vol/vol). Mustard essential oil was the most effective, likely due to the presence of allyl isothiocyanate, identified as its major component. Furthermore, mustard essential oil exhibited synergistic effects when combined with either Mexican oregano or thyme essential oils (fractional inhibitory concentration indices of 0.75); an additive effect was obtained by combining thyme and Mexican oregano essential oils (fractional inhibitory concentration index = 1.00). These results suggest the potential of studied essential oil mixtures to inhibit microbial growth and preserve foods; however, their effect on sensory quality in selected foods compatible with their flavor needs to be assessed.

In vitro activity of essential oils extracted from condiments against fluconazole-resistant and -sensitive Candida glabrata

In the present study, the antifungal activity of essential oils obtained from Origanum vulgare (oregano), Cinnamomum zeylanicum (cinnamon), Lippia graveolens (Mexican oregano), Thymus vulgaris (thyme), Salvia officinalis (sage), Rosmarinus officinalis (rosemary), Ocimum basilicum (basil) and Zingiber officinale (ginger) were assessed against Candida glabrata isolates. One group contained 30 fluconazole-susceptible C.glabrata isolates, and the second group contained fluconazole-resistant isolates derived from the first group after the in vitro induction of fluconazole-resistance, for a total of 60 tested isolates. The broth microdilution methodology was used. Concentrations of 50μg/mL, 100μg/mL, 200μg/mL, 400μg/mL, 800μg/mL, 1600μg/mL and 3200μg/mL of the essential oils were used, and the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) were determined. Thyme, sage, rosemary, basil and ginger essential oils showed no antifungal activity at the tested concentrations. Antimicrobial activity less than or equal to 3200μg/mL was observed for oregano, Mexican oregano and cinnamon essential oils. Both the oregano and Mexican oregano essential oils showed high levels of antifungal activity against the fluconazole-susceptible C.glabrata group, whereas the cinnamon essential oil showed the best antifungal activity against the fluconazole-resistant C.glabrata isolates.

Phytochemical diversity of the essential oils of Mexican Oregano (Lippia graveolens Kunth) populations along an Edapho-climatic gradient.

Mexican oregano (Lippia graveolens) is an important aromatic plant, mainly used as flavoring and usually harvested from non-cultivated populations. Mexican oregano essential oil showed important variation in the essential-oil yield and composition. The composition of the essential oils extracted by hydrodistillation from 14 wild populations of L. graveolens growing along an edaphoclimatic gradient was evaluated. Characterization of the oils by GC-FID and GC/MS analyses allowed the identification of 70 components, which accounted for 89-99% of the total oil composition. Principal component and hierarchical cluster analyses divided the essential oils into three distinct groups with contrasting oil compositions, viz., two phenolic chemotypes, with either carvacrol (C) or thymol (T) as dominant compounds (contents >75% of the total oil composition), and a non-phenolic chemotype (S) dominated by oxygenated sesquiterpenes. While Chemotype C was associated with semi-arid climate and shallower and rockier soils, Chemotype T was found for plants growing under less arid conditions and in deeper soils. The plants showing Chemotype S were more abundant in subhumid climate. High-oil-yield individuals (>3%) were identified, which additionally presented high percentages of either carvacrol or thymol; these individuals are of interest, as they could be used as parental material for scientific and commercial breeding programs.

Effect of Mexican Oregano (L ippia berlandieri Schauer) Essential Oil Fractions on the Growth of A spergillus spp. in a Bread Model System

Spices acting as antimicrobial agents can be used in combination with other factors to assure food safety. The aim of this work was to evaluate the effect of Mexican oregano (Lippia berlandieri Schauer) essential oil (EO) fractions on the growth of Aspergillus spp. using a bread model media. Fungal growth was evaluated on a wheat flour-based medium with controlled Aw (0.925, 0.950) and with five Mexican oregano EO fractions with different concentrations of thymol and carvacrol (50–200 mg/kg). Fungal growth (modified Gompertz equation) was affected by Aw values and the concentration of Mexican oregano EO fractions. Differences on thymol and carvacrol had no significant effect on the fungal growth kinetic parameters. Low Aw (0.925) and fractions with high concentration of carvacrol (1 and 2) at 100 mg/kg showed fungicidal activity. Combined methods for food preservation can include Mexican oregano EO, where Aspergillus spp. fungal growth can be inhibited. Practical Applications Incorporation of herbs and essential oils to food products can be considered as a good form to increase shelf life of the product, but usually data on antimicrobial and/or antioxidant capacity are performed under laboratory-controlled conditions. The development of predictive models that consider the effect of the food components on the effectiveness of natural antimicrobials can lead to a better understanding of the best conditions for their addition to food products. The present work describes the effect of water activity and wheat components on the antifungal activity of Mexican oregano essential oil. The composition of the essential oil and its concentration were tested in combination with water activity, and it was observed that those factors greatly affected the biological activity of the essential oil.

Aspergillus niger time to growth in dried tomatoes

Individual and combined effects of aw and incorporation of selected concentrations of Mexican oregano essential oil on the time to growth (TTG) of Aspergillus niger intentionally inoculated into dried tomatoes were studied during storage at 25°C for 100days. For aw 0.96, 1000ppm of Mexican oregano essential oil inhibited A. niger growth during 100days, whereas 500ppm were sufficient at aw 0.91 and 250ppm for tomatoes with aw 0.78. A. niger growth was evident at different incubation times depending on tested tomato aw and concentration of essential oil; these data were utilized to model TTG. Regression analysis revealed good agreement between experimental and predicted data with a correlation coefficient higher than 0.98. Analysis of mold growth data through TTG models makes possible to include observations detected as no growth and can be utilized to predict mold time to growth for specific preservation factor combinations or to select preservation factor levels for an expected shelf-life based on A. niger growth.

Microbiological Effect of Fermented Mexican Oregano (Lippia berlandieri Schauer) Waste

The antimicrobial properties of Mexican oregano (Lippia berlandieri Schauer) essential oil have been well documented; but its extraction process generates large amounts of agro-industrial wastes. This material can be used as support-substrate in solid-state fermentation, to release and/or accumulate molecules with industrial application. Therefore, the aim of this work was to evaluate the microbial effect of products derived from solid state fermentation of Mexican oregano waste by Aspergillus niger PSH. Microbial activity was tested by well diffusion test of aqueous and non-polar extracts from solid state fermentation, against fungi, foodborne pathogens and spoilage bacteria, as well as Lactic Acid Bacteria. Further, growth curves were done with Listeria monocytogenes and Lactobacillus lactis to describe the possible effect of extracts on bacterial growth. Polar and non-polar extracts from solid state fermentation had no deleterious effect against tested fungi and food-borne pathogenic bacteria (Escherichia coli O157:H7, Staphylococcus aureus, Salmonella enterica subgroup enterica subsp. Tiphymurium). Aqueous extract, at concentrations higher than 2.5 % had a bacteriostatic effect on L. monocytogenes. Lactic acid bacteria showed a growth increment in culture medium complemented with aqueous extracts, and this effect was confirmed by microbial growth curves. Non polar extracts had no antimicrobial effect. Aqueous extracts had a bacteriostatic effect in L. monocytogenes and promote the lactic acid bacteria growth; this extracts can be used as prebiotic or growth-enhancing supplement for lactic acid bacteria, but further research is needed.

Antifungal Effect of Mexican Oregano (Lippia berlandieri Schauer) Essential Oil on a Wheat Flour‐Based Medium

The antimicrobial activity of oregano has been attributed mainly to the presence of volatile compounds found in its essential oil (EO), mainly carvacrol and thymol. The search for antimicrobial activity of oregano EO with different concentrations of thymol and carvacrol, can lead to products with a wider range of applications. The aim of this work was to describe the in vitro antifungal effect of Mexican oregano (Lippia berlandieri Schauer) EO fractions on the growth of Aspergillus, Penicillium, and Rhizopus sp. The Mexican oregano EO fractions studied had different concentrations of carvacrol, which decreased from fraction 1 to 5 (81% to 23%), while thymol content increased from 3% to 64%. Fungal inhibition was evaluated on a wheat flour-based medium with EO fractions concentrations ranging from 50 to 200 mg/kg. Radial growth curves were fitted using the modified Gompertz model (R(2)(adj) = 0.989 ± 0.01). No significant differences (P > 0.05) were found with the different composition of the Mexican oregano EO fractions; nevertheless, fraction concentration presented significant (P < 0.05) mold inhibition as concentration increased. Rhizopus sp. (Rh18) showed a linear reduction on specific growth rate, on the maximum mold growth at the stationary phase, and an increase in the lag time as the concentration of the oregano EO increased; mold growth inhibition were achieved at 150 mg/kg in fractions 1 to 4, and at 100 mg/kg for fraction 5. Aspergillus sp. (As6) and Penicillium sp. (Pe36) were inhibited at 150 and 200 mg/kg, respectively. Results obtained suggest that Mexican oregano EO (Lippia berlandieri Schauer) compounds could be used as antimicrobial agents to prevent fungal growth in bakery products.

Antifungal activity evaluation of Mexican oregano (Lippia berlandieri Schauer) essential oil on the growth of Aspergillus flavus by gaseous contact.

The antifungal activity of Mexican oregano (Lippia berlandieri Schauer) essential oil by gaseous contact on the growth of Aspergillus flavus at selected essential oil concentrations (14.7, 29.4, 58.8, or 117.6 μl of essential oil per liter of air) and temperatures (25, 30, or 35°C) was evaluated in potato dextrose agar formulated at water activity of 0.98 and pH 4.0. Mold growth curves were adequately fitted (0.984 < R(2) < 0.999) by the modified Gompertz model. The effect of the independent variables (concentration of essential oil and temperature) on the estimated model parameters (reciprocal of growth rate [1/ν(m)] and lag time [λ]) were evaluated through polynomial equations. Both ν(m) and λ were significantly (P < 0.05) affected by the independent variables; ν(m) decreased and λ increased as essential oil concentration increased and temperature decreased, which suggests that Mexican oregano essential oil retards or inhibits mold germination stage. Further, minimum fungistatic and fungicide essential oil concentrations at 30 and 35°C were determined. Mexican oregano essential oil applied in gas phase exerts important antifungal activity on the growth of A. flavus, suggesting its potential to inhibit other food spoilage molds.

Antiviral activity of the Lippia graveolens (Mexican oregano) essential oil and its main compound carvacrol against human and animal viruses

Antiviral activity of the Lippia graveolens (Mexican oregano) essential oil and its main compound carvacrol against human and animal viruses

Antifungal activity by vapor contact of essential oils added to amaranth, chitosan, or starch edible films

Antimicrobial agents can be incorporated into edible films to provide microbiological stability, since films can be used as carriers of a variety of additives to extend product shelf life and reduce the risk of microbial growth on food surfaces. Addition of antimicrobial agents to edible films offers advantages such as the use of small antimicrobial concentrations and low diffusion rates. The aim of this study was to evaluate inhibition by vapor contact of Aspergillus niger and Penicillium digitatum by selected concentrations of Mexican oregano (Lippia berlandieri Schauer), cinnamon (Cinnamomum verum) or lemongrass (Cymbopogon citratus) essential oils (EOs) added to amaranth, chitosan, or starch edible films. Essential oils were characterized by gas chromatography-mass spectrometry (GC/MS) analysis. Amaranth, chitosan and starch edible films were formulated with essential oil concentrations of 0.00, 0.25, 0.50, 0.75, 1.00, 2.00, or 4.00%. Antifungal activity was evaluated by determining the mold radial growth on agar media inoculated with A. niger and P. digitatum after exposure to vapors arising from essential oils added to amaranth, chitosan or starch films using the inverted lid technique. The modified Gompertz model adequately described mold growth curves (mean coefficient of determination 0.991 ± 0.05). Chitosan films exhibited better antifungal effectiveness (inhibition of A. niger with 0.25% of Mexican oregano and cinnamon EO; inhibition of P. digitatum with 0.50% EOs) than amaranth films (2.00 and 4.00% of cinnamon and Mexican oregano EO were needed to inhibit the studied molds, respectively). For chitosan and amaranth films a significant increase (p<0.05) of lag phase was observed among film concentrations while a significant decrease (p<0.05) of maximum specific growth was determined. Chitosan edible films incorporating Mexican oregano or cinnamon essential oil could improve the quality of foods by the action of the volatile compounds on surface growth of molds.

Electrochemical Screening of Biomarkers in Chemotype Mexican Oregano Oils on Single‐Walled Carbon Nanotubes Screen‐Printed Electrodes

AbstractAn electrochemical screening for the determination of total biomarkers (thymol and carvacrol) of Lippia graveolens using single‐walled carbon nanotubes screen‐printed electrodes (SWCNT‐SPEs) is proposed. The suitability of the approach was demonstrated using GC‐MS by the analysis of selected Mexican oregano essential oil chemotypes. The analytical performance was excellent in terms of inter‐droplet precision (RSD≤6 %), sensitivity and linearity. An electrochemical index of biomarkers is proposed for fast assessment of oregano quality using just 50 µL of the sample. The route here proposed constitutes a very convenient screening tool in decentralized analysis because of the simplicity, disposability and easy‐to‐use by non‐specialist user.

Acaricidal Effect of Essential Oils From Lippia graveolens (Lamiales: Verbenaceae), Rosmarinus officinalis (Lamiales: Lamiaceae), and Allium sativum (Liliales: Liliaceae) Against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Acaricidal effects of three essential oils extracted from Mexican oregano leaves (Lippia graveolens Kunth), rosemary leaves (Rosmarinus officinalis L.), and garlic bulbs (Allium sativum L.) on 10-d-old Rhipicephalus (Boophilus) microplus (Canestrini) tick larvae were evaluated by using the larval packet test bioassay. Serial dilutions of the three essential oils were tested from a starting concentration of 20 to 1.25%. Results showed that both Mexican oregano and garlic essential oils had very similar activity, producing high mortality (90-100%) in all tested concentrations on 10-d-old R. microplus tick larvae. Rosemary essential oil produced >85% larval mortality at the higher concentrations (10 and 20%), but the effect decreased noticeably to 40% at an oil concentration of 5%, and mortality was absent at 2.5 and 1.25% of the essential oil concentration. Chemical composition of the essential oils was elucidated by gas chromatography-mass spectrometry analyses. Mexican oregano essential oil included thymol (24.59%), carvacrol (24.54%), p-cymene (13.6%), and y-terpinene (7.43%) as its main compounds, whereas rosemary essential oil was rich in a-pinene (31.07%), verbenone (15.26%), and 1,8-cineol (14.2%), and garlic essential oil was rich in diallyl trisulfide (33.57%), diallyl disulfide (30.93%), and methyl allyl trisulfide (11.28%). These results suggest that Mexican oregano and garlic essential oils merit further investigation as components of alternative approaches for R. microplus tick control.

Morphology and density of glandular trichomes in populations of Mexican oregano (Lippia graveolens H.B.K., Verbenaceae), and the relationship between trichome density and climate1

Abstract Despite the economic and therapeutic importance of Mexican oregano essential oil, there is no information regarding secretory structures and the effect of environmental factors on their density is unknown. The main goal of this study was to describe the morphology of glandular trichomes in Lippia graveolens H.B.K. (Verbenaceae), and evaluate the hypothesis that glandular trichome density on leaves of L. graveolens would be greatest for populations found in the most arid locations. Morphology and trichome density were investigated using a combination of scanning electron and stereoscopic microscopy in nine wild oregano populations. Emberger's index of aridity was calculated to characterize the populations located in a bio-climatic gradient. Correlation analysis was used to assess the relation between trichome density and aridity. Lippia graveolens presented two types of glandular trichome on both sides of the leaf: peltate and capitate, of which the former presented higher density. Geographic vari...

Antiviral activity of the Lippia graveolens (Mexican oregano) essential oil and its main compound carvacrol against human and animal viruses.

Mexican oregano (Lippia graveolens) is a plant found in Mexico and Central America that is traditionally used as a medicinal herb. In the present study, we investigated the antiviral activity of the essential oil of Mexican oregano and its major component, carvacrol, against different human and animal viruses. The MTT test (3–4,5-dimethythiazol-2yl)-2,5-diphenyl tetrazolium bromide) was conducted to determine the selectivity index (SI) of the essential oil, which was equal to 13.1, 7.4, 10.8, 9.7, and 7.2 for acyclovir-resistant herpes simplex virus type 1 (ACVR-HHV-1), acyclovir-sensitive HHV-1, human respiratory syncytial virus (HRSV), bovine herpesvirus type 2 (BoHV-2), and bovine viral diarrhoea virus (BVDV), respectively. The human rotavirus (RV) and BoHV-1 and 5 were not inhibited by the essential oil. Carvacrol alone exhibited high antiviral activity against RV with a SI of 33, but it was less efficient than the oil for the other viruses. Thus, Mexican oregano oil and its main component, carvacrol, are able to inhibit different human and animal viruses in vitro. Specifically, the antiviral effects of Mexican oregano oil on ACVR-HHV-1 and HRSV and of carvacrol on RV justify more detailed studies.