Anti-Coccal Activity and Composition of the Essential Oils and Methanolic Extracts Obtained from Brewing Quality Humulus lupulus L. Hop Pellets.

This study examined the chemical composition and anti-coccal properties of essential oils and methanolic extracts of six different Humulus lupulus L. varieties from Poland: Iunga, Marynka, Sybilla, Magnum, Tradition and Chinook. The activity of an α-acid-enriched fraction of methanolic extracts was also studied. The chemical composition of essential oils and extracts was determined by gas chromatography-mass spectrometry (GC/MS) and liquid chromatography-mass spectrometry (LC/MS) techniques. The compounds characteristic to H. lupulus extracts include xanthohumol, α-acids, ß-acids, and prenylated flavonoids. Essential oil compositions showed a high prevalence of monoterpene hydrocarbon, myrcene and sesquiterpene hydrocarbons, α-humulene and ß-caryophyllene. The antimicrobial activity was investigated against eight human cocci pathogenic strains: Staphylococcus aureus MRSA (ATCC 43300), S. aureus MRSA (29213), S. aureus MSSA (ATCC 29213), S. epidermidis (ATCC 12228), Enterococcus faecalis (ATCC 29212), E. faecalis VRE (ATCC 51299), E. faecium (ATCC 19434) and Micrococcus luteus (ATCC 10240). The lowest minimum inhibitory concentrations (MIC) were obtained for extracts and essential oils from Iunga hop samples. Extracts were significantly more active than essential oils. The most susceptible strain to both essential oils and extracts was M. luteus, whilst the least susceptible was E. faecium. The antimicrobial activity correlated with a high concentration of xanthohumol of active extracts rather than with the content of α-acids. Xanthohumol showed considerable activity against MRSA with an MIC value of 3.9 µg/mL. The activity of the α-acid-enriched fraction was mediocre compared to the results of all extracts.

Composition and Anti-Helicobacter pylori Properties of Essential Oils Obtained from Selected Mentha Cultivars.

Helicobacter pylori infections are highly common amongst the global population. Such infections have been shown to be the cause of gastric ulcers and stomach carcinoma and, unfortunately, most cases are asymptomatic. Standard treatment requires antibiotics such as metronidazole or azithromycin to which many strains are now resistant. Mentha species have been used as a natural treatment for gastrointestinal diseases throughout history and essential oils (EOs) derived from these plants show promising results as potential antimicrobial agents. In this study, EOs obtained from the leaves and flowers of five cultivars of Mentha × piperita and M. spicata were examined by GC-MS. The investigated mints are representatives of four chemotypes: the menthol chemotype (M. × piperita 'Multimentha' and M. × piperita 'Swiss'), the piperitenone oxide chemotype (M. × piperita 'Almira'), the linalool chemotype (M. × piperita 'Granada'), and the carvone chemotype (M. spicata 'Moroccan'). The chemical composition of EOs from mint flowers and leaves was comparable with the exception of the Swiss cultivar. Menthol was the most abundant component in the leaves while menthone was highest in flowers. The H. pylori ATCC 43504 reference strain and 10 other H. pylori clinical strains were examined for their sensitivity to the EOs in addition to their major monoterpenoid components (menthol, menthone, carvone, dihydrocarvone, linalool, 1,8-cineole, and limonene). All tested mint EOs showed inhibitory activity against both the reference H. pylori ATCC 43504 strain (MIC 15.6-31.3 mg/L) and clinical H. pylori strains (MIC50/90 31.3-250 mg/L/62.5-500 mg/L). Among the reference monoterpenes, menthol (MIC50/90 7.8/31.3 mg/L) and carvone (MIC50/90 31.3/62.5 mg/L) had the highest anti-H. pylori activity, which also correlated with a higher activity of EOs containing these compounds (M. × piperita 'Swiss' and M. spicata 'Moroccan'). A synergistic and additive interaction between the most active EOs/compounds and antibiotics possibly points to a new plant-based anti-H. pylori treatment.

Microbiological Studies on the Influence of Essential Oils from Several Origanum Species on Respiratory Pathogens.

Essential oils (EOs) with established and well-known activities against human pathogens might become new therapeutics in multidrug-resistant bacterial infections, including respiratory tract infections. The aim of this study was to evaluate the antimicrobial activity of EOs obtained from several samples of Origanum vulgare, O. syriacum, and O. majorana cultivated in Poland. EOs were analyzed by GC-MS and tested against four bacterial strains: Staphylococcus aureus (MRSA), Haemophilus influenzae, Haemophilus parainfluenzae, and Pseudomonas aeruginosa. Chemical analyses showed that the Eos were characterized by a high diversity in composition. Based on the chemical data, four chemotypes of Origanum EOs were confirmed. These were carvacrol, terpineol/sabinene hydrate, caryophyllene oxide, and thymol chemotypes. Thin-layer chromatography-bioautography confirmed the presence of biologically active antibacterial components in all tested EOs. The highest number of active spots were found among EOs with cis-sabinene hydrate as the major compound. On the other hand, the largest spots of inhibition were characteristic to EOs of the carvacrol chemotype. Minimal inhibitory concentrations (MICs) were evaluated for the most active EOs: O. vulgare 'Hirtum', O. vulgare 'Margarita', O. vulgare 'Hot & Spicy', O. majorana, and O. syriacum (I) and (II); it was shown that both Haemophilus strains were the most sensitive with an MIC value of 0.15 mg/mL for all EOs. O. majorana EO was also the most active in the MIC assay and had the highest inhibitory rate in the anti-biofilm assay against all strains. The most characteristic components present in this EO were the trans-sabinene hydrate and terpinen-4-ol. The strain with the least sensitivity was the MRSA with an MIC of 0.6 mg/mL for all EOs except for O. majorana, where the MIC value reached 0.3 mg/mL. Scanning electron microscopy performed on the Haemophilus influenzae and Haemophilus parainfluenzae biofilms showed a visible decrease in the appearance of bacterial clusters under the influence of O. majorana EO.

Composition, Anti-MRSA Activity and Toxicity of Essential Oils from Cymbopogon Species.

Many of the essential oils obtained from medicinal plants possess proven antimicrobial activity and are suitable for medicinal purposes and applications in the food industry. The aim of the present work was the chemical analysis of 19 essential oils (EOs) from seven different Cymbopogon species (C. nardus, C. citratus, C winterianus, C. flexuosus, C. schoenanthus, C. martinii, C. giganteus). Five different chemotypes were established by GC/MS and TLC assay. The EOs, as well as some reference compounds, i.e., citronellol, geraniol and citral (neral + geranial), were also tested for their antimicrobial and antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA) by the microdilution method and direct bioautography. The toxicity of EOs was evaluated by Danio rerio 'Zebrafish' model assay. All examined EOs showed moderate to high activity against MRSA, with the highest activity noted for C. flexuosus-lemongrass essential oil, both in microdilution and direct autobiography method. Significant difference in the toxicity of the examined EOs was also detected.