Étude de six huiles essentielles : composition chimique et activité antibactérienne

Activity of Patchouli and Tea Tree Essential Oils against Staphylococci Isolated from Pyoderma in Dogs and Their Synergistic Potential with Gentamicin and Enrofloxacin

In this paper, we show the effect of some essential oils (EOs) on staphylococci, including multidrug-resistant strains isolated from pyoderma in dogs. A total of 13 Staphylococcus pseudintermedius and 8 Staphylococcus aureus strains were studied. To assess the sensitivity of each strain to the antimicrobial agents, two commercial EOs from patchouli (Pogostemon cablin; PcEO) and tea tree (Melaleuca alternifolia; MaEO) as well as two antibiotics (gentamicin and enrofloxacin) were used. The minimum inhibitory concentration (MIC) followed by checkerboards in the combination of EO-antibiotic were performed. Finally, fractional inhibitory concentrations were calculated to determine possible interactions between these antimicrobial agents. PcEO MIC ranged from 0.125 to 0.5 % v/v (1.2-4.8 mg/mL), whereas MaEO MIC was tenfold higher (0.625-5% v/v or 5.6-44.8 mg/mL). Gentamicin appeared to be highly prone to interacting with EOs. Dual synergy (38.1% of cases) and PcEO additive/MaEO synergism (53.4%) were predominantly observed. On the contrary, usually, no interactions between enrofloxacin and EOs were observed (57.1%). Both commercial EOs were characterized by natural composition without artificial adulteration. Patchouli and tea tree oils can be good alternatives for treating severe cases of pyoderma in dogs, especially when dealing with multidrug-resistant strains.

Thirteen Dipterocarpoideae genomes provide insights into their evolution and borneol biosynthesis

Dipterocarpoideae, the largest subfamily of the Dipterocarpaceae, is a dominant component of Southeast Asian rainforests and is widely used as a source of wood, damar resin, medicine, and essential oil. However, many Dipterocarpoideae species are currently on the IUCN Red List owing to severe degradation of their habitats under global climate change and human disturbance. Genetic information regarding these taxa has only recently been reported with the sequencing of four Dipterocarp genomes, providing clues to the function and evolution of these species. Here, we report on 13 high-quality Dipterocarpoideae genome assemblies, ranging in size from 302.6 to 494.8 Mb and representing the five most species-rich genera in Dipterocarpoideae. Molecular dating analyses support the Western Gondwanaland origin of Dipterocarpaceae. Based on evolutionary analysis, we propose a three-step chromosome evolution scenario to describe the karyotypic evolution from an ancestor with six chromosomes to present-day species with 11 and 7 chromosomes. We discovered an expansion of genes encoding cellulose synthase (CesA), which is essential for cellulose biosynthesis and secondary cell-wall formation. We functionally identified five bornyl diphosphate synthase (BPPS) genes, which specifically catalyze the biosynthesis of borneol, a natural medicinal compound extracted from damar resin and oils, thus providing a basis for large-scale production of natural borneol in vitro.

Chemical Composition and Bioinsecticidal Effects of Thymus zygis L., Salvia officinalis L. and Mentha suaveolens Ehrh. Essential Oils on Medfly Ceratitis capitata and Tomato Leaf Miner Tuta absoluta

The present work was aimed to study the toxicity of the essential oils of three aromatic and medicinal plants on the tomato leaf miner Tuta absoluta and the Medfly Ceratitis capitata as an alternative to conventional pesticides. We carried out a phytochemical and insecticide study of T. zygis L., S. officinalis L. and M. suaveolens Ehrh. essential oils (EOs) through the study of their chemical composition and their toxicity on C. capitata adults and T. absoluta larvae. The extraction of the EOs by hydrodistillation showed yields of 3.87 ± 0.03, 4.09 ± 0.23 and 4.35 ± 0.11 for T. zygis, S. officinalis L. and M. suaveolens Ehrh., respectively. The identification of the chemical composition of the EOs by GC/MS showed that oxygenated monoterpenes constituted the most abundant group for all the extracted EOs. The major compounds were rather diversified depending on plant species. In fact, the S. officinalis L. EO mainly contained trans-thujone (21.80 %), the M. suaveolens Ehrh. EO mainly contained piperitenone oxide (71.19%), and carvacrol (61.60%) was the main component of the T. zygis L. EO. An insecticidal effect was observed for the three studied EOs on C. capitata adults and T. absoluta larvae. The observed LD₅₀ values were 0.80 µL/mL and 11.04 µL/mL for M. suaveolens and S. officinalis, respectively, on T. absoluta larvae. For C. capitata adults, the obtained LD₅₀ values were 0.9 µL/mL and 11.78 µL/mL for M. suaveolens and T. zygis, respectively. The presented findings could contribute to the development of biopesticides for plants as a component of integrated pest management strategies in citrus and tomato crops.

The Tagetes lucida Cav. essential oil and the mixture of its main compounds are antibacterial and modulate antibiotic resistance in multi-resistant pathogenic bacteria

We evaluated an essential oil (EO) of Tagetes lucida Cav. and the mixture of its main compounds against multi-drug resistant bacteria. We found that EO and the partially reconstituted blend of its main components have antibacterial activity and inhibit antibiotic resistance (ampicillin, chloramphenicol, nalidixic acid, vancomycin, and imipenem) in strains of Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa HIM-MR01. The T. lucida EO alone or added to the antibiotics showed antimicrobial activity against S. aureus and P. aeruginosa. The EO main bioactive compounds were methyl eugenol (46.15%), estragole (32.93%), linalool (2.48%), and geraniol (0.33%). The mixture (PREO) of those compounds at those proportions inhibited the growth of P. aeruginosa in 45% at 683.62 µg mL^-1 and that of S. aureus in 51.7% at 39.04 µg mL^-1 . The PREO had higher antibacterial and modulatory activities than the original EO. In conclusion, we overcame the unpredictability of EO activity (due to their natural variability) by determining which EO components inhibited bacteria and then producing a PREO to generate a reproducible mixture with predictable antibacterial and modulation of resistance activities. Thus, the PREO, and its components, show potential as alternatives to manage multidrug-resistant pathogens.

Antimicrobial resistance profile of Staphylococcus aureus and its in-vitro potential inhibition efficiency

BACKGROUND

Staphylococcus aureus infection is associated with hospitals and caused mortality in hospitalized patients. These biofilm-forming bacteria are associated with chronic infections in patients.

OBJECTIVES

To investigate the biofilm forming ability of multidrug resistant bacteria associated with hospital environment and analyze anti-biofilm compounds from the natural sources.

METHODS

The hospital wastewater sample was used for the isolation of drug resistant S. aureus strains. The biofilm producing ability was analyzed and the isolated S. aureus strains were tested for antibiotic susceptibility patterns against various antibiotics. To screen suitable antibacterial agent, essential oil was extracted from Teucrium polium by hydrodistillation method and the compounds were determined by GC-MS analysis. The antimicrobial potential of essential oil was studied against S. aureus strains by disc diffusion method and biofilm inhibition property of essential oil was analyzed. The synergistic activity of essential oil was also analyzed.

RESULTS

A total of 13 S. aureus strains were isolated and almost all bacterial strains showed biofilm forming ability. Most of the isolated S. aureus strains showed resistance to ampicillin, cefoxitin, ciprofloxacin, erythromycin, gentamicin, chloramphenicol and vancomycin. The extracted essential oil showed pale yellow in colour with pleasant odour and the yield was about 0.9%. Twenty-two compounds were detected in GC-MS analysis which shared about 96% of the total determined chemical composition. The major compounds determined were α-pinene (5.3%), linalool (16.2%), caryophyllene (10.04%), germacrene D (37.2%), and β-eudesmol (6.1%). The extracted essential oil showed antibacterial activity and the zone of inhibition varied from 15 ± 1 to 21 ± 2 mm against S. aureus strains. The essential oil showed antibiofilm activity and synergistic activity against S. aureus strains.

CONCLUSIONS

This study analyzed biofilm forming ability of drug resistant S. aureus strains isolated from the hospital wastewater. The isolated bacterial strains showed resistance against various tested antibiotics. The essential oil extracted from T. polium showed antibacterial and anti-biofilm activity.

Chemical Profile, Antioxidant Capacity, and Antimicrobial Activity of Essential Oils Extracted from Three Different Varieties (Moldoveanca 4, Vis Magic 10, and Alba 7) of Lavandula angustifolia

Chemical composition, antioxidant capacity, and antimicrobial activity of lavender essential oils (LEOs) extracted from three different varieties of Lavandula angustifolia Mill. (1-Moldoveanca 4, 2-Vis magic 10, and 3-Alba 7) have been determined. These plants previously patented in the Republic of Moldova were cultivated in an organic agriculture system in the northeastern part of Romania and then harvested in 3 consecutive years (2017-2019) to obtain the essential oils. From the inflorescences in the complete flowering stage, the LEOs were extracted by hydrodistillation. Then, their composition was analyzed by gas chromatography coupled with mass spectrometry (GC-MS) and by Fourier Transformed Infrared spectroscopy (FT-IR). The major identified constituents are as follows: linalool (1: 32.19-46.83%; 2: 29.93-30.97%; 3: 31.97-33.77%), linalyl acetate (1: 17.70-35.18%; 2: 27.55-37.13%; 3: 28.03-35.32%), and terpinen-4-ol (1: 3.63-7.70%; 2: 3.06-7.16%; 3: 3.10-6.53%). The antioxidant capacity as determined by ABTS and DPPH assays indicates inhibition, with the highest activity obtained for LEO var. Alba 7 from 2019. The in vitro antimicrobial activities of the LEOs and combinations were investigated as well, by using the disk diffusion method and minimum inhibitory concentration (MIC) against the Gram-positive bacterial strain Staphylococcus aureus (ATCC 6538), Gram-negative Pseudomonas aeruginosa (ATCC 27858), Escherichia coli (ATCC 25922), the yeast Candida albicans (ATCC 10231), and clinical isolates. Our results have shown that LEOs obtained from the three studied varieties of L. angustifolia manifest significant bactericidal effects against tested microorganisms (Staphylococcus aureus and Escherichia coli), and antifungal effects against Candida albicans. The mixture of LEOs (Var. Alba 7) and geranium, respectively, in tea tree EOs, in different ratios, showed a significant enhancement of the antibacterial effect against all the studied strains, except Pseudomonas aeruginosa.

Chemical Composition and Antimicrobial Activity of Artemisia herba-alba and Origanum majorana Essential Oils from Morocco

Essential oils (EOs) are one of the most important groups of plant metabolites responsible for their biological activities. This study was carried out to study the chemical composition and the antimicrobial effects of Artemisia herba-alba and Origanum majorana essential oils against some Gram-positive and Gram-negative bacteria, and a fungal strain isolated from spoiled butter. The plants were collected in the region Azzemour of South West Morocco and the EOs, extracted by hydrodistillation, were analyzed by GC-MS. The antimicrobial activity was determined using the agar paper disc method. The main components of A. herba-alba EO were cis-thujone, trans-thujone and vanillyl alcohol; in O. majorana EO terpinen-4-ol, isopulegol and β-phellandrene predominated. Both essential oils exhibited growth inhibiting activities in a concentration-dependent manner on several microorganism species. Our results demonstrated that O. majorana and A. herba-alba EOs could be effective natural antibacterial agents in foods.

Antimicrobial Activity of Some Essential Oils-Present Status and Future Perspectives

Extensive documentation on the antimicrobial properties of essential oils and their constituents has been carried out by several workers. Although the mechanism of action of a few essential oil components has been elucidated in many pioneering works in the past, detailed knowledge of most of the compounds and their mechanism of action is still lacking. This knowledge is particularly important for the determination of the effect of essential oils on different microorganisms, how they work in combination with other antimicrobial compounds, and their interaction with food matrix components. Also, recent studies have demonstrated that nanoparticles (NPs) functionalized with essential oils have significant antimicrobial potential against multidrug- resistant pathogens due to an increase in chemical stability and solubility, decreased rapid evaporation and minimized degradation of active essential oil components. The application of encapsulated essential oils also supports their controlled and sustained release, which enhances their bioavailability and efficacy against multidrug-resistant pathogens. In the recent years, due to increasingly negative consumer perceptions of synthetic preservatives, interest in essential oils and their application in food preservation has been amplified. Moreover, the development of resistance to different antimicrobial agents by bacteria, fungi, viruses, parasites, etc. is a great challenge to the medical field for treating the infections caused by them, and hence, there is a pressing need to look for new and novel antimicrobials. To overcome these problems, nano-encapsulation of essential oils and exploiting the synergies between essential oils, constituents of essential oils, and antibiotics along with essential oils have been recommended as an answer to this problem. However, less is known about the interactions that lead to additive, synergistic, or antagonistic effects. A contributing role of this knowledge could be the design of new and more potent antimicrobial blends, and understanding of the interplay between the components of crude essential oils. This review is written with the purpose of giving an overview of current knowledge about the antimicrobial properties of essential oils and their mechanisms of action, components of essential oils, nano-encapsulated essential oils, and synergistic combinations of essential oils so as to find research areas that can facilitate applications of essential oils to overcome the problem of multidrug-resistant micro-organisms.

Investigation of the antifungal activity of carvacrol against strains of Cryptococcus neoformans

BACKGROUND

Cryptococcus neoformans is the etiologic agent of opportunistic systemic fungal infection cryptococcosis, which affects individuals with compromised immune systems. Thus, natural products research has become important, since monoterpenes such as carvacrol, a promising molecule in the search antifungal agents, have shown significant biological activity.

OBJECTIVE

The study aimed to investigate the antifungal activity and mode of action of carvacrol against strains of C. neoformans.

METHODS

The minimum inhibitory concentration (MIC) was determined by microdilution method. Minimum fungicidal concentration (MFC) was performed by seeding technique on solid media. Studying the mode of action was performed using broth microdilution.

RESULTS

The MIC ranged from 25 to 81 μg/mL and the MFC ranged from 25 to 102 μg/mL. Carvacrol bonded to exogenous ergosterol and cholesterol.

DISCUSSION

The results suggest that carvacrol has antifungal activity against C. neoformans and its mode of action is related to fungal membrane instability.

CONCLUSIONS

The phytoconstituent carvacrol may eventually become a drug; however, further studies are needed to elucidate its mechanism.