Testing the antimicrobial activity of essential oils

The vapor phase of some essential oils proved to have antimicrobial activity. Utilization of the vapor phase of Eos is presently understood as one of the possible alternatives to synthetic food preservatives which could be used in the future. However, testing the vapor phase of EOs against microorganisms causing food-borne diseases (e.g. Salmonella enteritidis or Staphylococcus aureus) or food spoilage is relatively new. Consequently, due to the large number of known EOs, research on their antimicrobial activity is still largely in the phase of in vitro rather than in vivo testing. Moreover, no standard and reliable method for fast screening of a wide range of samples exists. Thus, the aim of this study is to show results concerning tests of the antimicrobial activity of EOs against S. enteritidis or S. aureus, which were conducted by two modifications of the disc volatilization method we developed. The lately developed method has the potential to become widely used for fast screening of EO antimicrobial activity in the vapor phase

Secreted Enzyme-Responsive System for Controlled Antifungal Agent Release

[EN] Essential oil components (EOCs) such as eugenol play a significant role in plant antimicrobial defense. Due to the volatility and general reactivity of these molecules, plants have evolved smart systems for their storage and release, which are key prerequisites for their efficient use. In this study, biomimetic systems for the controlled release of eugenol, inspired by natural plant defense mechanisms, were prepared and their antifungal activity is described. Delivery and antifungal studies of mesoporous silica nanoparticles (MSN) loaded with eugenol and capped with different saccharide gates-starch, maltodextrin, maltose and glucose-against fungus Aspergillus niger-were performed. The maltodextrin- and maltose-capped systems show very low eugenol release in the absence of the fungus Aspergillus niger but high cargo delivery in its presence. The anchored saccharides are degraded by exogenous enzymes, resulting in eugenol release and efficient inhibition of fungal growth.This research was funded by the project NutRisk (Project No: CZ.02.1.01/0.0/0.0/16_019/0000845), the Spanish Government (projects RTI2018-100910-B-C41, RTI2018-101599-B-C22-AR and RTI2018-101599-B-C21-AR (MINECO/FEDER)) and the GeneralitatValenciana (project PROME-TEO 2018/024); by the National Agency for Agricultural Research of the Ministry of Agriculture of the Czech Republic under project Biostore QK21010064; and by the Research Infrastructure METROFOOD-CZ supported by the Ministry of Education, Youth, and Sports of the Czech Republic under project number LM201810. A.B. thanks the Spanish Government for financial support.Bernardos Bau, A.; Bozik, M.; Montero, A.; Pérez-Esteve, É.; García-Casado, E.; Lhotka, M.; Frankova, A.... (2021). Secreted Enzyme-Responsive System for Controlled Antifungal Agent Release. Nanomaterials. 11(5):1-14. https://doi.org/10.3390/nano11051280S11411

Thymoquinone vapor significantly affects the results of Staphylococcus aureus sensitivity tests using the standard broth microdilution method

The broth microdilution (BMD) method is widely used for the determination of minimum inhibitory concentrations of antimicrobial agents, including volatile oils and their components. In this series of various experiments, we have demonstrated the influence of thymoquinone (TQ) vapor on the results of the BMD test performed with Staphylococcus aureus as a model organism. The spread of vapor from the TQ containing wells (32–512 μg/mL) caused the complete inhibition of staphylococcal growth in adjoining wells initially containing bacterium-inoculated pure Mueller–Hinton broth only and thus produced false positive results of the test. The ability of TQ to pass into the adjoined wells was subsequently confirmed by gas chromatography–mass spectrometry, whereas TQ at concentrations up to 84 μg/mL was detected in these wells after five hours. Based on these results, we suppose that vapors of TQ as well as of other naturally occurring volatile compounds and their mixtures (for example essential oils and plant extracts) can significantly influence results of the standard BMD assay. These observations, therefore, call for development of new appropriate BMD method suitable for assessment of antimicrobial activity of volatile substances

Effect of solar drying on the composition of essential oil of Sacha culantro (Eryngium foetidum L.) grown in the Peruvian Amazon

Two solar drying methods (direct cabinet solar dryer and indirect cabinet solar dryer) were tested under tropical conditions for drying aerial parts of sacha culantro (Eryngium foetidum L.) in Pucallpa City (Peruvian Amazon). The drying behavior was monitored during all experimental runs. Dried samples and fresh leaves were hydrodistilled and isolated oils were analyzed using gas chromatography with flame ionization detector and gas chromatography-mass spectrometry. (E)-2-dodecenal was determined as the main constituent of the sacha culantro essential oil, averaging 61.8–62.2%, followed by n-dodecanal (10.9–15.5%), (E)-2-tetradecenal (6.7–7.6%) and 1-tetradecene (3.6–5.7%). When comparing both solar drying methods, the indirect method was found as more suitable for drying E. foetidum since the dried product resembled the fresh herb more closely in its chemicalcomposition and had better appearance. However, a better drying efficiency of 10.3% was achieved when drying in the direct solar dryer compared with 5.8% for the indirect solar dryer

Evaluation of antimicrobial and anti-inflammatory activities of seed extracts from six Nigella species

Seed extracts from six species of the genus Nigella (Family Ranunculaceae)—Nigella arvensis, Nigella damascena, Nigella hispanica, Nigella nigellastrum, Nigella orientalis, and Nigella sativa—obtained by successive extraction with n-hexane, chloroform, and methanol, were tested for their antimicrobial activity against 10 strains of pathogenic bacteria and yeast using the microdilution method as well as for anti-inflammatory properties by in vitro cyclooxygenase (COX)-1 and COX-2 assay. Chemical characterization of active extracts was carried out including free and fixed fatty acid analysis. Comparison of antimicrobial activity showed that N. arvensis chloroform extract was the most potent among all species tested, inhibiting Gram-positive bacterial and yeast strains with minimum inhibitory concentration (MIC) values ranging from 0.25 to 1 mg/mL. With the exception of selective inhibitory action of n-hexane extract of N. orientalis on growth of Bacteroides fragilis (MIC = 0.5 mg/mL), we observed no antimicrobial activity for other Nigella species. Anti-inflammatory screening revealed that N. sativa, N. orientalis, N. hispanica, N. arvensis n-hexane, and N. hispanica chloroform extracts had strong inhibitory activity (more than 80%) on COX-1 and N. orientalis, N. arvensis, and N. hispanica n-hexane extracts were most effective against COX-2, when the concentration of extracts was 100 μg/mL in both COX assays. In conclusion, N. arvensis, N. orientalis, and N. hispanica seeds, for the first time examined for antimicrobial and anti-inflammatory effects, revealed their significant activity in one or both assays

Norsesquiterpene hydrocarbon, chemical composition and antimicrobial activity of Rhaponticum carthamoides root essential oil

A detailed analysis of Rhaponticum carthamoides (Willd.) Iljin root essential oil was carried out by GC, GC–MS and GC–FTIR techniques. In total, 30 components were identified, accounting for 98.0% of total volatiles. A norsesquiterpene 13-norcypera-1(5),11(12)-diene (22.6%), followed by aplotaxene (21.2%) and cyperene (17.9%), were isolated and their structures confirmed by 1D and 2D-NMR spectra (COSY, ROESY, HSQC, HMBC and INADEQUATE). Selinene type sesquiterpenes and aliphatic hydrocarbons were among minor constituents of the essential oil. The oil exhibited antimicrobial activity against 5 of 9 strains of bacteria and yeast, when tested using broth micro-dilution method. Minimum inhibitory concentrations ranged between 32 and 256 μg/ml

Metabolism of Selected 2-Arylbenzofurans in a Colon In Vitro Model System

2-arylbenzofurans represent a small group of bioactive compounds found in the plant family Moraceae. As it has not been investigated whether these substances are stable during passage through the gastrointestinal tract, their biological effects may be altered by the metabolism of intestinal microbiota or cells. The aim of the present study was to investigate and compare mulberrofuran Y (1), moracin C (2), and mulberrofuran G (3) in an in vitro model of human intestinal bacterial fermentation and in an epithelial model using the Caco-2 cell line. The analysis of compounds by LC-MS-Q-TOF showed sufficient stability in the fermentation model, with no bacterial metabolites detected. However, great differences in the quantity of permeation were observed in the permeability assay. Moreover, mulberrofuran Y (1) and moracin C (2) were observed to be transformed into polar metabolites by conjugation. Among the test compounds, mulberrofuran Y (1) was mostly stable and accumulated in endothelial cells (85.3%) compared with mulberrofuran G (3) and moracin C (2) (14% and 8.2%, respectively). Thus, only a small amount of mulberrofuran Y (1) was conjugated. Moracin C (2) and mulberrofuran G (3) were metabolized almost completely, with only traces of the unchanged molecule being found on the apical and cellular sides of the system. Only conjugates of mulberrofuran Y (1) and moracin C (2) were able to reach the basolateral side. Our results provide the basic description of bioavailability of these three compounds, which is a necessary characteristic for final evaluation of bio-efficacy

In Vitro. antimicrobial activity of some Libyan medicinal plant extracts

In vitro. antimicrobial activity of 32 extracts (ethanol, hexane, chloroform, and methanol) from eight different Libyan medicinal plants, namely Artemisia herba-alba. Asso (Compositae), Globularia alypum. L. (Globulariaceae), Helichrysum stoechas., DC. (Compositae), Peganum harmala. L. (Zygophyllaceae), Polygonum equisetiforme. Sibth. & Sm. (Polygonaceae), Pulicaria crispa. (Forssk.) Oliv. (Compositae), Rosmarinus officinalis. L. (Labiatae), and Thymus capitatus. Hoffmanns & Link. (Labiatae), was determined against seven bacteria and one yeast strain using the broth microdilution method. The results show that all plants tested possessed antimicrobial activity against at least one of the examined strains at a concentration ≤8 mg/ml. The extracts from H. stoechas., P. equisetiforme., P. crispa., R. officinalis., and T. capitatus. exhibited strongest activity against Gram-positive bacteria with minimum inhibitory concentrations (MICs) ranging from 0.5 to 8 mg/ml. Only a few extracts showed inhibitory activity against Gram-negative strains in this test, whereas those of the H. stoechas. and P. harmala. were among the strongest ones (MICs range 4–8 mg/ml). High anticandidal activity was observed for P. harmala., P. crispa., and T. capitatus., with MICs ranging from 0.25 to 1 mg/ml

Metabolism of Stilbenoids by Human Faecal Microbiota

Stilbenoids are dietary phenolics with notable biological effects on humans. Epidemiological, clinical, and nutritional studies from recent years have confirmed the significant biological effects of stilbenoids, such as oxidative stress protection and the prevention of degenerative diseases, including cancer, cardiovascular diseases, and neurodegenerative diseases. Stilbenoids are intensively metabolically transformed by colon microbiota, and their corresponding metabolites might show different or stronger biological activity than their parent molecules. The aim of the present study was to determine the metabolism of six stilbenoids (resveratrol, oxyresveratrol, piceatannol, thunalbene, batatasin III, and pinostilbene), mediated by colon microbiota. Stilbenoids were fermented in an in vitro faecal fermentation system using fresh faeces from five different donors as an inoculum. The samples of metabolized stilbenoids were collected at 0, 2, 4, 8, 24, and 48 h. Significant differences in the microbial transformation among stilbene derivatives were observed by liquid chromatography mass spectrometry (LC/MS). Four stilbenoids (resveratrol, oxyresveratrol, piceatannol and thunalbene) were metabolically transformed by double bond reduction, dihydroxylation, and demethylation, while batatasin III and pinostilbene were stable under conditions simulating the colon environment. Strong inter-individual differences in speed, intensity, and pathways of metabolism were observed among the faecal samples obtained from the donors

Essential oils in the Ranunculaceae family: chemical composition of hydrodistilled oils from Consolida regalis, Delphinium elatum, Nigella hispanica, and N. nigellastrum seeds

In this study, we analyzed the chemical composition of volatile oils hydrodistilled from seeds of Consolida regalis, Delphinium elatum, Nigella hispanica, and N. nigellastrum using GC and GC/MS. In C. regalis, octadecenoic (77.79%) and hexadecanoic acid (8.34%) were the main constituents. Similarly, the oils from D. elatum and N. hispanica seeds consisted chiefly of octadecadienoic (42.83 and 35.58%, resp.), hexadecanoic (23.87 and 28.59%, resp.), and octadecenoic acid (21.67 and 19.76%, resp.). Contrastingly, the monoterpene hydrocarbons α-pinene (34.67%) and β-pinene (36.42%) were the main components of N. nigellastrum essential oil. Our results confirm the presence of essential oils in the family Ranunculaceae and suggest chemotaxonomical relationships within the representatives of the genera Consolida, Delphinium, and Nigella. In addition, the presence of various bioactive constituents such as linoleic acid, (−)-β-pinene, squalene, or carotol in seeds of D. elatum, N. hispanica, and N. nigellastrum indicates a possible industrial use of these plants