Extraction of the essential oil from endemic Origanum bilgeri P.H.Davis with two different methods: comparison of the oil composition and antibacterial activity

The antibacterial activity and chemical composition of the essential oils (EOs) isolated from Origanum bilgeri P.H.Davis by two different extraction methods, i.e., hydrodistillation (HD) and solvent-free microwave extraction (SFME), were examined. This endemic Origanum species had shown very good antibacterial activity. The composition of the O. bilgeri EOs obtained by SFME and HD was investigated by GC/MS analysis. The main components of the oils obtained by both methods were carvacrol (90.20-84.30%), p-cymene (3.40-5.85%), γ-terpinene (0.47-1.20%), and thymol (0.69-1.08%). The EO isolation by SFME offered many important advantages, including a higher extraction yield, a shorter extraction time, and a higher content of the active component carvacrol. The carvacrol-rich oils obtained by both HD and SFME showed a good antibacterial activity. The largest inhibition zones were observed for the O. bilgeri EO obtained by SFME. Our study suggests that O. bilgeri EO has the potential to be used as preventative against bacterial contamination in many foods, instead of the common synthetic antimicrobial products.     

Inhibitory efficacy of different essential oils against storage carrot rot with antifungal and resistance‐inducing potential

The inhibitory effects of essential oils (EOs) derived from coriander, lavender, geranium, thyme, savoury and eucalyptus were assessed against Sclerotinia sclerotiorum, the causal agent of carrot white mould. All EOs showed antifungal activity against the pathogen in vitro and in vivo. In addition, all EOs markedly increased 6‐methoxymellein in the treated carrots. The EOs of thyme and savoury were found to be more effective than other tested EOs. The enzymatic tests showed that thyme and savoury EOs were more able than lavender EO to significantly increase the level of chitinases, peroxidases, β‐1,3‐glucanases, polyphenol oxidase, peroxidase and phenylalanine ammonia‐lyase in the treated carrots, indicating that the EOs of thyme and savoury have potential to be considered as effective inducers of resistance against carrot white mould. In this study, all EOs inhibited myceliogenic and carpogenic germination of sclerotia at concentrations 1 and 10 µl/ml sterile distilled water, respectively. After gas chromatography/mass spectrometry, major component in the thyme EO was found to be thymol (39.15%) followed by p‐cymene (13.85%) and carvacrol (10.36%), while in savoury EO were carvacrol (41.9%), γ‐terpinene (17.38) and p‐cymene (11.25%).     

Anti-biofilm activities of essential oils rich in carvacrol and thymol against Salmonella Enteritidis

The aim of the present study was to determine the bioactive compounds in four essential oils (EO’s) from Origanum heracleoticum, Origanum vulgare, Thymus vulgaris and Thymus serpyllum and to assess their antimicrobial and anti-biofilm activity against Salmonella Enteritidis. Strains were previously characterized depending on the expression of the extracellular matrix components cellulose and curli fimbriae as rdar (red, dry and rough) and bdar morphotype (brown, dry and rough). This study revealed that the EO’s and EOC’s (carvacrol and thymol) investigated showed inhibition of biofilm formation at sub-minimum inhibitory concentration. Comparing the efficacy of EO’s and EOC’s in the inhibition of biofilm formation between the strains with different morphotype (rdar and bdar) did not show a statistically significant difference. Results related to the effectiveness of EO’s and EOC’s (the essential oil components, carvacrol and thymol) on eradication of preformed 48?h old biofilms indicated that biofilm reduction occurred in a dose-dependent manner over time.     

Chemometric Tools to Highlight the Variability of the Chemical Composition and Yield of Lebanese Origanum syriacum L. Essential Oil

This study deals with the variation in the yield and composition of Lebanese Origanum syriacum L. essential oil (EO) according to harvesting time, drying methods used, and geographical location. Plant material was harvested twice a month all over 2013 and 2014 from Qartaba and Achkout located at high altitude and from Byblos at low altitude. EOs of the aerial parts were obtained by hydrodistillation. The highest yields were obtained at full flowering stage and slightly reduced after flowering. The GC/MS analysis revealed the presence of 50 components representing 90.49 – 99.82%, 88.79 – 100%, and 95.28 – 100% of the total oil extracted from plants harvested from Qartaba, Achkout, and Byblos, respectively. The major components in the oils were: carvacrol (2.1 – 79.8%), thymol (0.3 – 83.7%), p‐cymene (2.8 – 43.8%), thymoquinone (0.4 – 27.7%), γ‐terpinene (0.4 – 10.0%), octan‐3‐ol (0.3 – 4.9%), caryophyllene oxide (0.2 – 4.7%), oct‐1‐en‐3‐ol (0.3 – 3.7%), β‐caryophyllene (0.7 – 3.2%), cis‐sabinene hydrate (0.1 – 2.8%), terpinen‐4‐ol (0.1 – 2.8%), and α‐terpinene (0.2 – 2.2%). Independent components analysis (ICA) revealed that two groups were discriminated, reflecting compositional differences in the EOs profiles of the Lebanese oregano samples: O. syriacum grown in Qartaba and Achkout belongs to carvacrol chemotype, while O. syriacum grown in Byblos belongs to thymol chemotype. The flowering phase was the most productive period in terms of yield, bringing marked changes in the EO composition by increasing the amounts of carvacrol or thymol, and decreasing those of thymoquinone and p‐cymene.     

Antimicrobial and antioxidant activities of Mexican oregano essential oils (Lippia graveolens H. B. K.) with different composition when microencapsulated inβ‐cyclodextrin

Aims: To study how the antimicrobial and antioxidant activities of Lippia graveolens essential oils with different composition are affected after the microencapsulation process with β‐cyclodextrin (βCD). Methods and results: Three Mexican oregano essential oils (EOs) with different carvacrol/thymol/p‐cymene ratios (38 : 3 : 32, 23 : 2 : 42, 7 : 19 : 35) were used in this study. Microencapsulation was carried out by spray‐drying. Antimicrobial activities were measured as MBC (minimal bactericidal concentration) using 0·05%/0·10%/0·20% (w/v) dilutions of EOs against Escherichia coli ATCC 11229, Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538. Antioxidant activities were determined by the 2,2′‐diphenyl‐1‐picrylhydrazil (DPPH) method. EOs showed antimicrobial and antioxidant activity, but microencapsulation preserved the antimicrobial activity in all cases and increased the antioxidant activity from four‐ to eightfold. Conclusions: Although the Lippia essential oils were from the same species, their composition affects the biological activities before and after the microencapsulation process, as well as encapsulation efficiency. Our study supports the fact that microencapsulation of EOs in β‐cyclodextrin preserves the antimicrobial activity, improves the antioxidant activity and acts as a protection for EOs main compounds. Significance and Impact of the Study: Microencapsulation affects positively EOs main compounds, improves antioxidant activity and retains antimicrobial activity, enhancing the quality of the oils.     

Susceptibility of food-borne bacteria to binary combinations of antimicrobials at selected a(w) and pH

AIM: To evaluate the antibacterial susceptibilities of food-borne bacteria to individual and binary mixtures of a synthetic antimicrobial agent with a natural phenolic compound. METHODS AND RESULTS: Antibacterial susceptibilities of Escherichia coli, Listeria innocua, Salmonella Typhimurium and Staphylococcus aureus to individual and binary mixtures of potassium sorbate with a phenolic compound (thymol, carvacrol, or eugenol) were evaluated, at selected water activity (a(w); 0.99 or 0.97) and pH (5.5 or 4.5). The bacteria studied were susceptible to the action of the antimicrobials individually with minimal inhibitory concentrations that varied from 800-ppm potassium sorbate for Staph. aureus at a(w) 0.99, and pH 5.5 to 100-ppm thymol or carvacrol for the four studied bacteria at a(w) 0.97 and pH 4.5. Several binary mixtures of potassium sorbate with thymol, carvacrol or eugenol inhibited bacterial growth. Antimicrobial agent inhibitory concentrations in the mixture varied among bacteria, additionally depending on the a(w) and the pH tested. CONCLUSIONS: Synergistic binary mixtures with fractional inhibitory concentration index <0.6 include 100- or 200-ppm potassium sorbate with 50- or 100-ppm thymol, carvacrol or eugenol. SIGNIFICANCE AND IMPACT OF THE STUDY: The synergistic combinations could be useful in reducing the amounts of antimicrobials needed to inhibit growth, thus diminishing consumer concerns regarding chemical preservatives.     

Impact of Colored Shade Nets on Biomass Production,Essential Oil Composition and Orientin and Isoorientin Content in Lippia gracilis Schauer

The objective of this study was to evaluate the effect of ChromatiNet on vegetative growth, total antioxidant capacity, phenolic and essential oils (EOs) composition of Lippia gracilis. The plants were cultivated under full sunlight, black, blue and red ChromatiNet. The flavonoid content and antioxidant capacity were quantified spectrophotometrically. The C-glycosylflavone isomers (orientin and isoorientin) were isolated and identified by conventional spectroscopic techniques and measured using high-performance liquid chromatography-diode array detection. The EO was analysed by gas chromatography and gas chromatography-mass spectrometry. Environment influenced growth, total antioxidant capacity and phytochemical levels. Shoot dry weight, thymol, carvacrol and (E)-caryophyllene were favoured under red and black ChromatiNet. Root growth, EOs, caryophyllene oxide, p-cymene, flavonoids, orientin and isoorientin were favoured in sunlight. Growth and accumulation of EOs, flavonoids and photosynthetic pigments increased under blue ChromatiNet. Therefore, Lippia gracilis plants have plasticity related to the spectral quality of light and it cultivate depends of the phytochemicals of interest.     

Efficacies of Nisin A and Nisin V Semipurified Preparations Alone and in Combination with Plant Essential Oils for Controlling Listeria monocytogenes

The food-borne pathogenic bacterium Listeria is known for relatively low morbidity and high mortality rates, reaching up to 25 to 30%. Listeria is a hardy organism, and its control in foods represents a significant challenge. Many naturally occurring compounds, including the bacteriocin nisin and a number of plant essential oils, have been widely studied and are reported to be effective as antimicrobial agents against spoilage and pathogenic microorganisms. The aim of this study was to investigate the ability of semipurified preparations (SPP) containing either nisin A or an enhanced bioengineered derivative, nisin V, alone and in combination with low concentrations of the essential oils thymol, carvacrol, and trans-cinnamaldehyde, to control Listeria monocytogenes in both laboratory media and model food systems. Combinations of nisin V-containing SPP (25 μg/ml) with thymol (0.02%), carvacrol (0.02%), or cinnamaldehyde (0.02%) produced a significantly longer lag phase than any of the essential oil-nisin A combinations. In addition, the log reduction in cell counts achieved by the nisin V-carvacrol or nisin V-cinnamaldehyde combinations was twice that of the equivalent nisin A-essential oil treatment. Significantly, this enhanced activity was validated in model food systems against L. monocytogenes strains of food origin. We conclude that the fermentate form of nisin V in combination with carvacrol and cinnamaldehyde offers significant advantages as a novel, natural, and effective means to enhance food safety by inhibiting food-borne pathogens such as L. monocytogenes.     

Effects of dietary thymol‐carvacrol on growth performance,hematological parameters and tissue composition of juvenile rainbow trout,Oncorhynchus mykiss

Growth performance, carcass quality, survival and hematological responses of Oncorhynchus mykiss juveniles (initial weight 8.4 ± 0.1 g) fed diets containing thymol‐carvacrol powder at the levels of 0, 1.0, 2.0, 3.0 g kg^?1 were tested. Thymol‐carvacrol powder originated from Origanum vulgare, a Mediterranean plant, added to diets. Each diet was fed to triplicate groups of fish for 45 days. Fish fed diets containing thymol‐carvacrol had significantly higher final weight and growth than the control group. Food conversion ratio in fish fed diets containing 2.0 and 3.0 g kg^?1 thymol‐carvacrol was statistically better than in other treatments. Survival was not different among all treatments. The number of lymphocytes increased when thymol‐carvacrol was used at higher levels. Furthermore, whole body lipid content was higher in fish fed 1.0 and 2.0 g kg^?1 thymol‐carvacrol than the other groups, but body protein in the group fed 3.0 g kg^?1 was higher than in other groups. Also, body ash in control and 1.0 g kg^?1 was higher than in other groups. Whole body dry matter was not affected by dietary treatments. These results indicated that dietary administration of thymol‐carvacrol can influence some growth, hematological parameters and tissue composition in rainbow trout juveniles.     

Antiproliferative Effect of Essential Oil Obtained from Oregano (Lippia palmeri S. Watson) Leaves Grown in Hydroponics and LED Light

Nowadays, light-emitting diodes (LED) provide an alternative source to sunlight with specific intensity and wavelength that promotes plant growth. The features offered by LED could also stimulate the production of secondary metabolites of pharmaceutical interest. This work analyzed the cultivation of oregano (Lippia palmeri S. Watson) in a floating root hydroponic system supplemented by full-spectrum LED artificial light. Growth indicators like height, diameter, number of shoots, and leaf length and width were measured. The essential oil (EO) composition from the leaves of wild and hydroponic conditions found thymol (41.8 %) as the main product for the former and carvacrol (47 %) in hydroponics. The antiproliferative activity of EOs on human colorectal cancer HCT-15 shows that 6.4 μg/ml for hydroponic and 7.4 μg/ml for the wild plant reduce more than 50 % the cell viability. Overall, this study indicates that hydroponic conditions and full spectrum LED modifies the composition of the EO of L. palmeri on compared with the wild plant, which effectively induces cell growth inhibition in human colorectal cancer.     

Essential Oil Variability and Biological Activities of Tetraclinis articulata (Vahl) Mast. Wood According to the Extraction Time

In the present work, the hydrodistillation (HD) and microwave‐assisted hydrodistillation (MAHD) kinetics of essential oil (EO) extracted from Tetraclinis articulata (Vahl ) Mast. wood was conducted, in order to assess the impact of extraction time and technique on chemical composition and biological activities. Gas chromatography (GC) and GC/mass spectrometry analyses showed significant differences between the extracted EOs, where each family class or component presents a specific kinetic according to extraction time, technique and especially for the major components: camphene, linalool, cedrol, carvacrol and α‐acorenol. Furthermore, our findings showed a high variability for both antioxidant and anti‐inflammatory activities, where each activity has a specific effect according to extraction time and technique. The highlighted variability reflects the high impact of extraction time and technique on chemical composition and biological activities, which led to conclude that we should select EOs to be investigated carefully depending on extraction time and technique, in order to isolate the bioactive components or to have the best quality of EO in terms of biological activities and preventive effects in food.     

Essential Oil of Deverra tortuosa Aerial Parts: Detailed Chemical Profile,Allelopathic, Antimicrobial,and Antioxidant Activities

Essential oils (EOs) are a promising group of natural products of the aromatic plants due to their various biological effects such as allelopathic, antioxidant, antimicrobial activities. The present study aimed to construct the detailed chemical profile of the EO derived from Deverra tortuosa aerial parts along with assessing its allelopathic, antimicrobial, and antioxidant potentialities. The EO was extracted by hydrodistillation and analyzed via gas chromatography-mass spectrometry (GC/MS). The allelopathic activity of the EO was assessed against the germination and seedling growth of the weed Chenopodium murale. Also, the EO was tested against five microbes. The antioxidant activity was determined using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The GC/MS analysis of EO revealed the presence of 86 compounds with a preponderance of oxygenated sesquiterpenes and monoterpene hydrocarbons. Widdrol, β-phellandrene, piperitol, cubedol, α-terpinene, (E)-10-heptadecen-8-ynoic acid methyl ester, citronellyl tiglate, and m-cymene were the major compounds. A comparative profile was established between the EOs constituents of our study with the documented EOs of D. tortuosa and the other Deverra species around the world via agglomerative hierarchical clustering (AHC) and principal components analysis (PCA). The EO showed a substantial allelopathic activity against C. murale, as well as it showed considerable antimicrobial and antioxidant activities. Thereby, the EO of D. tortuosa could be considered as a promising environmental-friendly bioherbicide against weeds. Also, it could be integrated into food preservation due to its potent antimicrobial and antioxidant activities. However, further study is recommended for more characterization of the major compounds and evaluation of their activities, either singular or synergistic, and assess their efficiency and biosafety.     

Chemical composition and antimicrobial activity of Cymbopogon citratus and Cymbopogon giganteus essential oils alone and in combination

As part of ongoing research on the chemical composition and the antimicrobial properties of Burkinabe plants essential oils alone and in combination, essential oils (EOs) from leaves of Cymbopogon citratus and Cymbopogon giganteus from Burkina Faso were analyzed by GC-FID and GC-MS. Five constituents, which accounted for 96.3% of the oil, were identified in the EO of C. citratus. Geranial (48.1%), neral (34.6%) and myrcene (11.0%) were the major constituents. For C. giganteus a total of eight compounds were identified which represented 86.0% of the oils extracted. The dominant compounds were limonene (42%) and a set of monoterpene alcohols: trans-p-mentha-1(7),8-dien-2-ol (14.2%), cis-p-mentha-1(7),8-dien-2-ol (12%), trans-p-mentha-2,8-dien-1-ol (5.6%) and cis-p-mentha-2,8-dien-1-ol (5.2%). The EOs were tested against nine bacteria by using disc diffusion and microdilution methods. C. giganteus EO showed antimicrobial effects against all microorganisms tested whereas C. citratus EO failed to inhibit Pseudomonas aeruginosa. The antimicrobial activity of combinations of the two EOs was quantified by the checkerboard method. Combinations of the two EOs exerted synergistic, additive and indifferent antimicrobial effects. Results of the present investigation provide evidence that the combinations of plant EOs could be assessed for synergistic activity in order to reduce their minimum effective dose.     

Chemical composition, antioxidant and antimicrobial activities of essential oil of Thymus algeriensis wild-growing in Libya

The composition of essential oil isolated from Thymus algeriensis growing wild in Libya was analyzed by GC and GC-MS. The essential oil was characterized with thymol (38.50%) as the major component. The oil was screened for antioxidant activity using DPPH assay, and compared to thymol and carvacrol. Antioxidant activity was high, with the IC₅₀ of 0.299 mg/ml, compared to 0.403 and 0.105 mg/ml for thymol and carvacrol, and 0.0717 mg/ml for BHA. In addition, antimicrobial activity was tested against eight bacteria and eight fungi. T. algeriensis oil showed inhibitory activity against tested bacteria at 0.001–0.05 mg/ml, while bactericidal activity (MBC) was achieved at 0.0025–0.05 mg/ml. For antifungal activity MICs ranged 0.0005–0.025 mg/ml and MFC 0.001–0.05 mg/ml. High antimicrobial activity against the fungi in particular suggests that the essential oil of Thymus algeriensis could have a useful practical application.     

Effects of dose and formulation of carvacrol and thymol on bacteria and some functional traits of the gut in piglets after weaning

Two trials were conducted to study the effects of dose and formulation of carvacrol and thymol on bacterial counts, metabolites and functional traits of the gut in weaned piglets. In the first experiment (Exp. I), 25 piglets (28 d, 6.59 ± 0.48 kg BW) were allocated to five dietary treatments: a control diet, or the same diet supplemented with either carvacrol or thymol at doses of 500 and 2000 mg kg^?1. In the second experiment (Exp. II), 35 piglets (28 d, 7.99 ± 0.73 kg BW) were assigned to seven dietary treatments: the same control diet as in Exp. I, or this diet supplemented with thymol in one of three formulations (on celite, on alphacel or microencapsulated) at doses of 500 and 2000 mg kg^?1. At 11/12 days post-weaning piglets were euthanised, and digesta from stomach, proximal and distal small intestine were sampled for bacteriological and biochemical analysis. Small intestinal tissue was sampled for histo-morphological determinations. In none of the experiments or sections of the gut was the number of bacteria lowered by the carvacrol or thymol supplementation. In Exp. I, the villus/crypt ratio at the distal small intestine for the experimental diets (1.30–1.32) was higher than for the control diet (1.24) (p < 0.05). Thymol fed animals in Exp. II had a lower number of intra-epithelial lymphocytes at the proximal (p < 0.05) and at the distal (p < 0.1) small intestine as compared to control animals. Mean concentration of the active ingredient in the stomach and proximal small intestine for the 2000 mg kg^?1 carvacrol diet was 521 and 5 mg kg^?1 fresh digesta, respectively, and for the 2000 mg kg^?1 thymol diets it ranged between 475 and 647 and between 13 and 24 mg kg^?1 fresh digesta, respectively. Cumulative absorption in the proximal small intestine was higher than 90% for all treatments and was not affected by formulation type. These data suggest that carvacrol and thymol can improve gut health, but evidence for clear antimicrobial effects towards the major culturable bacteria of the pig foregut is limited.     

Variation in Phytochemical,Morphological, and Ploidy Levels of Iranian Thymus Species

Thymus is one of the most important genera of the Lamiaceae family. This work was performed to assess inter and intra species variation, which is an indispensable prerequisite for the selection and the exploitation of the germplasm, using yield, secondary metabolites, and ploidy level criteria. Nineteen Iranian populations belonging to 11 Thymus species which includes T. vulgaris were used in this study. The results of cytological observations on the 19 populations revealed the three root-tip chromosome numbers of 2n=2x=30, 2n=4x=56 or 60 (diploid and tetraploid). This study also presents the results of a two-year field experiment that evaluates the agronomic and morphology of the 19 populations of Thymus spp. Cluster analysis grouped the populations into six groups and explained the relationships among ploidy levels, morphological traits, and essential oils (EOs). In general, diploid species belonged to the thymol chemotype, whilst carvacrol chemotype consistently dependent on the gene-dosage effect. Thymus migricus, T. daenensis-2, T. serpyllum, and T. trautvetteri populations with diverse thymol background were the best selection as the parents to improve thymol in a breeding program. Moreover, dry and fresh weight criteria can be used to improve EO content in thyme. Achieving this goal would be expected by crossing T. migricus and T. daenensis-2. Finally, providing relevant information on the ploidy level of Thymus species, with emphasis on morphology and EO components variations, may be recommended for the selection of populations or species to improve bioactive components as well as morphological traits in future breeding programs.     

The antibacterial mechanism of carvacrol and thymol against Escherichia coli

Aims:  To investigate the antibacterial mechanism of carvacrol and thymol against Escherichia coli.
Methods and Results:  The time-kill curve results showed that carvacrol and thymol at 200 mg l⁻¹ could inhibit the growth of E. coli . Flow cytometry and fluorescent dyes were used to explore the effect of two components on membrane permeability and membrane potential. In membrane permeability experiment, the mean fluorescence intensity of cells treated with 200 mg l⁻¹ carvacrol or thymol were lower than nonexposed cells. The ratio of red to green fluorescence intensity of DiOC₂(3) reflected the change of membrane potential. Carvacrol and thymol at 200 mg l⁻¹ caused the ratio of red/green decreasing from 0·42 of control to 0·08 and 0·07, respectively.
Conclusions:  Carvacrol and thymol had desired antimicrobial effect on E. coli . The antibacterial effects were attributed to their ability to permeabilize and depolarize the cytoplasmic membrane.
Significance and Impact of the Study:  This study showed the potential use of flow cytometry as a suitable method to investigate the mode of antibacterial action of essential oil components.     

Chemical Composition and Antimicrobial Activity of the Essential Oil of Ruta chalepensis L. Growing Wild in Lebanon

The essential oils (EOs) isolated from the fresh aerial parts of Ruta chalepensis L. collected in North Lebanon were obtained by solvent‐free microwave extraction (Milestone®), yielding 0.12% EO from both the leaves and a mixture of stems and leaves. The EOs were characterized by GC/MS analysis, and 27 components were identified, which were primarily ketones (88.0–93.2%). The main components were nonan‐2‐one and undecan‐2‐one. The antimicrobial activity of the EOs against a Gram‐positive and a Gram‐negative bacterium, a yeast, and a dermatophyte was evaluated using the broth‐microdilution technique and expressed as minimal inhibitory concentration (MIC). The EOs revealed moderate in vitro antifungal activity against Trichophyton rubrum and Candida albicans.     

Chemical Composition and Activity of Essential Oils of Carissa macrocarpa (Eckl.) A.DC. Cultivated in Tunisia and Its Anatomical Features

This is the first study investigating the chemical composition of essential oils (EOs) isolated from different tissues of Carissa macrocarpa (Eckl .) A.DC., their antimicrobial activity and the anatomical characters of the aerial organs and the fruits. The main EO components were pentadecanal and tetradecan‐1‐ol (31.9 and 16.5% in fresh leaf EO, respectively), (E)‐nerolidol and caryophyllene oxide (27.3 and 15.0% in fruit EO, respectively), linalool and hexahydrofarnesyl acetone (30.9 and 24.9% in stem EO, respectively), benzyl benzoate (24.3% in flower EO). The fruit EO was more active against Candida albicans (MIC = 0.46 mg/mL) compared to the reference antibiotic (17.66 mg/mL). Furthermore, at this concentration it inhibited all the Gram‐positive bacteria. Concerning the anatomical features, it is noteworthy to mention the presence of a large cluster of calcium oxalate crystals inside some parenchymatous cells. Large ducts corresponding to non articulated laticifers were identified in the cortex of leaf, stem and fruit pericarp. The laticifers categories and their distribution are taxonomically important to discriminate this species from others acclimated in different countries. Considering the obtained results, EOs of C. macrocarpa can be a good source of antimicrobial compounds, contributing to solve the problem of microbial resistance to antibiotics.     

Chemical composition and synergistic effect of three Moroccan lavender EOs with ciprofloxacin against foodborne bacteria: a promising approach to modulate antimicrobial resistance

The aim of this study was to determine the chemical profile of the essential oils (EOs) of three Moroccan lavender species (Lavandula pedunculata, LP; Lavandula angustifolia, LA; and Lavandula maroccana, LM) and to investigate, for the first time, the synergistic effect of the optimal mixture of the EOs with conventional antibiotic ciprofloxacin against three pathogenic foodborne bacteria. Gas chromatography/mass spectrometry analysis showed that eucalyptol (39·05%), camphor (24·21%) and borneol (8·29%) were the dominant compounds of LA-EO. LP-EO was characterized by the abundance of camphor (74·51%) and fenchone (27·06%), whereas carvacrol (42·08%), camphor (17·95%) and fenchone (12·05%) were the main constituents of LM-EO. EOs alone or combined showed a remarkable antimicrobial activity against the tested bacteria with minimum inhibitory concentrations (MICs) ranging from 3·53 to 15·96 mg ml⁻¹. The optimal mixture, calculated using a mixture design, corresponded to 19% LA, 38% LP and 43% LM. All combination of the EOs and the best EO mixture with ciprofloxacin exhibited a total synergism with fractional inhibitory concentration index values ranging from 0·27 to 0·37. The best EO mixture showed the highest gain of 128-fold, especially against Salmonella spp., more than that found testing the EOs separately. These findings should be taken into consideration for a possible application in the pharmaceutical and food industries.