Thymus zygis Essential Oil: Phytochemical Characterization, Bioactivity Evaluation and Synergistic Effect with Antibiotics against Staphylococcus aureus

Essential Oil Constituents as Anti-Inflammatory and Neuroprotective Agents: An Insight through Microglia Modulation

Microglia are key players in the brain's innate immune response, contributing to homeostatic and reparative functions but also to inflammatory and underlying mechanisms of neurodegeneration. Targeting microglia and modulating their function may have therapeutic potential for mitigating neuroinflammation and neurodegeneration. The anti-inflammatory properties of essential oils suggest that some of their components may be useful in regulating microglial function and microglial-associated neuroinflammation. This study, starting from the ethnopharmacological premises of the therapeutic benefits of aromatic plants, assessed the evidence for the essential oil modulation of microglia, investigating their potential pharmacological mechanisms. Current knowledge of the phytoconstituents, safety of essential oil components, and anti-inflammatory and potential neuroprotective effects were reviewed. This review encompasses essential oils of Thymus spp., Artemisia spp., Ziziphora clinopodioides, Valeriana jatamansi, Acorus spp., and others as well as some of their components including 1,8-cineole, β-caryophyllene, β-patchoulene, carvacrol, β-ionone, eugenol, geraniol, menthol, linalool, thymol, α-asarone, and α-thujone. Essential oils that target PPAR/PI3K-Akt/MAPK signalling pathways could supplement other approaches to modulate microglial-associated inflammation to treat neurodegenerative diseases, particularly in cases where reactive microglia play a part in the pathophysiological mechanisms underlying neurodegeneration.

Carvacrol and Thymol Content Affects the Antioxidant and Antibacterial Activity of Origanum compactum and Thymus zygis Essential Oils

Essential oils are of great interest due to their potent pharmaceutical and biological activities. In this study, essential oils extracted from Origanum compactum and Thymus zygis originating from the Middle Atlas of Morocco were investigated. Their chemical compositions were analyzed using gas chromatography and mass spectrometry, while the assessment of the trapping power of the radical (DPPH: 1,1-diphenyl-2-picrylhydrazyl) and the reducing antioxidant potential of ferric ions (FRAP: Ferric Reducing Antioxidant Power) were performed in order to evaluate the antioxidant activity. Their antibacterial potency was tested against six bacterial strains through the disk diffusion method. The chromatography analyses of the extracted essential oils highlighted the presence of two main components, namely carvacrol at 75.70% in O. compactum and thymol at 40.67% in T. zygis. The antioxidant activity tests showed that both essential oils demonstrated a significant antioxidant activity comparable to the positive control (e.g., ascorbic acid). The antibacterial activity results showed a strong antimicrobial effect for both essential oils, compared to synthetic antibiotics. This study affirms the presence of bioactive components with interesting antioxidant and antibacterial activities in the essential oils extracted from Origanum compactum and Thymus zygis, which could find several applications in the food and pharmaceutical industries through the substitution of synthetic antioxidants and antibiotics.

Flowering phenophases influence the antibacterial and anti-biofilm effects of Thymus vulgaris L. essential oil

BACKGROUND

Essential oils are becoming increasingly popular in medicinal applications because of their antimicrobial effect. Thymus vulgaris L. (Lamiaceae) is a well-known and widely cultivated medicinal plant, which is used as a remedy for cold, cough and gastrointestinal symptoms. Essential oil content of thyme is responsible for its antimicrobial activity, however, it has been reported that the chemical composition of essential oils influences its biological activity. In order to explore flowering phenophases influence on the chemical composition of thyme essential oil and its antibacterial and anti-biofilm activity, plant materials were collected at the beginning of flowering, in full bloom and at the end of flowering periods in 2019.

METHODS

Essential oils from fresh and dried plant materials were distilled and analyzed with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID). The antibacterial activity was performed by broth microdilution and thin layer chromatography-direct bioautography (TLC-DB) assays and the anti-biofilm effect by crystal violet assay, respectively. Scanning electron microscopy was applied to illustrate the cellular changes of bacterial cells after essential oil treatment.

RESULTS

Thymol (52.33-62.46%) was the main component in the thyme essential oils. Thyme oil distilled from fresh plant material and collected at the beginning of flowering period exerted the highest antibacterial and anti-biofilm activity against Haemophilus influenzae, H. parainfluenzae and Pseudomonas aeruginosa.

CONCLUSION

The different flowering periods of Thymus vulgaris influence the antibacterial and anti-biofilm activity of its essential oils, therefore, the collection time has to be taken into consideration and not only the full bloom, but the beginning of flowering period may provide biological active thyme essential oil.

A simple and efficient fluorescent labeling method in Staphylococcus aureus for real-time tracking of invasive bacteria

Bacterial fluorescent labeling is a powerful tool for the diagnosis and treatment of bacterial infections. Here, we present a simple and efficient labeling strategy for Staphylococcus aureus. Intracellular labeling of bacteria was achieved by heat shock using Cyanine 5.5 (Cy5.5) near-infrared-I dyes in S. aureus (Cy5.5@S. aureus). Several key factors, such as Cy5.5 concentration and labeling time, were systematically evaluated. Further, the cytotoxicity of Cy5.5 and the stability of Cy5.5@S. aureus was evaluated by flow cytometry, inverted fluorescence microscopy, and transmission electron microscopy. In addition, Cy5.5@S. aureus were used to explore the phagocytic behavior of RAW264.7 macrophages. These results proved that Cy5.5@S. aureus had a uniform fluorescence intensity and high luminance; additionally, our method had no significant adverse effects on S. aureus compared to unlabeled S. aureus infections. Our method provides researchers with a useful option for analyzing the behavior of S. aureus as an infectious agent. This technique can be broadly applied to study host cell-bacteria interactions at the molecular level, and to in vivo tracing of bacterial infections.

Synergistic and Antibiofilm Effects of the Essential Oil from Croton conduplicatus (Euphorbiaceae) against Methicillin-Resistant Staphylococcus aureus

Bacterial resistance refers to the ability of bacteria to resist the action of some antibiotics due to the development of adaptation and resistance mechanisms. It is a serious public health problem, especially for diseases caused by opportunistic bacteria. In this context, the search for new drugs, used alone or in combination, appears as an alternative for the treatment of microbial infections, and natural products, such as essential oils, are important in this process due to their structural diversity, which increases the probability for antimicrobial action. The objective of this study was to extract and identify the chemical components of the essential oil from Croton conduplicatus (EOCC), to evaluate the antimicrobial activity, to investigate the effect of the interaction between the EOCC and different antibiotics and to evaluate its antibiofilm potential. The EOCC was obtained by hydrodistillation. Based on chemical characterisation, 70 compounds were identified, with 1.8 cineole (13.15%), p-cymene (10.68%), caryophyllene (9.73%) and spathulenol (6.36%) being the major constituents. The minimum inhibitory concentration (MIC) values of EOCC were 256 and 512 µg mL^-1 for methicillin-sensitive and -resistant Staphylococcus aureus strains (MSSA and MRSA), respectively. The combinations of EOCC with the antibiotics oxacillin and ampicillin were synergistic (OXA/EOCC and AMP/EOCC combined decreased the OXA MIC and AMP MIC to 0.5 and 0.25 for MSSA, respectively, and OXA/EOCC and AMP/EOCC combined decreased the OXA MIC and the AMP MIC to 1 and 0.5 for MRSA, respectively) and could modify the resistance profile of MSSA and MRSA strains. The results indicated that EOCC was also able to partially inhibit biofilm formation. Our study presents important information about the chemical composition of EOCC and its antimicrobial potential and provides a reference to determine the mechanisms of action of EOCC and its use in pharmaceutical formulations.

Potential of Aromatic Plant-Derived Essential Oils for the Control of Foodborne Bacteria and Antibiotic Resistance in Animal Production: A Review

Antibiotic resistance has become a severe public threat to human health worldwide. Supplementing antibiotic growth promoters (AGPs) at subtherapeutic levels has been a commonly applied method to improve the production performance of livestock and poultry, but the misuse of antibiotics in animal production plays a major role in the antibiotic resistance crisis and foodborne disease outbreaks. The addition of AGPs to improve production performance in livestock and poultry has been prohibited in some countries, including Europe, the United States and China. Moreover, cross-resistance could result in the development of multidrug resistant bacteria and limit therapeutic options for human and animal health. Therefore, finding alternatives to antibiotics to maintain the efficiency of livestock production and reduce the risk of foodborne disease outbreaks is beneficial to human health and the sustainable development of animal husbandry. Essential oils (EOs) and their individual compounds derived from aromatic plants are becoming increasingly popular as potential antibiotic alternatives for animal production based on their antibacterial properties. This paper reviews recent studies in the application of EOs in animal production for the control of foodborne pathogens, summarizes their molecular modes of action to increase the susceptibility of antibiotic-resistant bacteria, and provides a promising role for the application of nanoencapsulated EOs in animal production to control bacteria and overcome antibiotic resistance.

Essential Oils as a Dietary Additive for Small Ruminants: A Meta-Analysis on Performance, Rumen Parameters, Serum Metabolites, and Product Quality

There is an increasing pressure to identify natural feed additives that improve the productivity and health of livestock, without affecting the quality of derived products. The objective of this study was to evaluate the effects of dietary supplementation with essential oils (EOs) on productive performance, rumen parameters, serum metabolites, and quality of products (meat and milk) derived from small ruminants by means of a meta-analysis. Seventy-four peer-reviewed publications were included in the data set. Weighted mean differences (WMD) between the EOs treatments and the control treatment were used to assess the magnitude of effect. Dietary inclusion of EOs increased (p < 0.05) dry matter intake (WMD = 0.021 kg/d), dry matter digestibility (WMD = 14.11 g/kg of DM), daily weight gain (WMD = 0.008 kg/d), and feed conversion ratio (WMD = −0.111). The inclusion of EOs in small ruminants’ diets decreased (p < 0.05) ruminal ammonia nitrogen concentration (WMD = −0.310 mg/dL), total protozoa (WMD = −1.426 × 105/mL), methanogens (WMD = −0.60 × 107/mL), and enteric methane emissions (WMD = −3.93 L/d) and increased ruminal propionate concentration (WMD = 0.726 mol/100 mol, p < 0.001). The serum urea concentration was lower (WMD = −0.688 mg/dL; p = 0.009), but serum catalase (WMD = 0.204 ng/mL), superoxide dismutase (WMD = 0.037 ng/mL), and total antioxidant capacity (WMD = 0.749 U/mL) were higher (p < 0.05) in response to EOs supplementation. In meat, EOs supplementation decreased (p < 0.05) the cooking loss (WMD = −0.617 g/100 g), malondialdehyde content (WMD = −0.029 mg/kg of meat), yellowness (WMD = −0.316), and total viable bacterial count (WMD = −0.780 CFU/g of meat). There was higher (p < 0.05) milk production (WMD = 0.113 kg/d), feed efficiency (WMD = 0.039 kg/kg), protein (WMD = 0.059 g/100 g), and lactose content in the milk (WMD = 0.100 g/100 g), as well as lower somatic cell counts in milk (WMD = −0.910 × 103 cells/mL) in response to EOs supplementation. In conclusion, dietary supplementation with EOs improves productive performance as well as meat and milk quality of small ruminants. In addition, EOs improve antioxidant status in blood serum and rumen fermentation and decrease environmental impact.

Antiviral and Antibacterial Effect of Honey Enriched with Rubus spp. as a Functional Food with Enhanced Antioxidant Properties

The aim of this study was to investigate the effect of blackberry and raspberry fruits (1 and 4%) and leaves (0.5 and 1%) on the biological activities of rape honey. Honey and plant material extracts were analyzed regarding total phenolic, flavonoid, anthocyanin contents, HPTLC and HPLC polyphenol profiles, as well as antioxidant activity. The antiviral potential was analyzed against bacteriophage phi 6-a coronavirus surrogate-whereas antimicrobial was tested against S. aureus and E. coli. Blackberry extracts were more abundant in antioxidants than raspberry extracts, with better properties found for leaves than fruits and for cultivated rather than commercial plants. The addition of both Rubus plant additives significantly increased the antioxidant potential of honey by four-fold (for 4% fruits additive) to five-fold (for 1% of leaves). Honey with the addition of fruits possessed higher antiviral potential compared with raw rape honey (the highest for 4% of raspberry fruit and 1% of blackberry leaf additive). Honey enriched with Rubus materials showed higher antibacterial potential against S. aureus than rape honey and effectively inhibited S. aureus biofilm formation. To summarize, honey enriched with Rubus fruit or leaves are characterized by increased pro-health value and can be recommended as a novel functional food.

Synergistic Action of AMX Associated with 1,8-Cineole and Its Effect on the ESBL Enzymatic Resistance Mechanism

The purpose of the present study is twofold. First, it aims to evaluate the synergistic action of the ß-lactam antibiotic; AMX is associated with 1,8-cineole on six clinical isolates of ESBL-producing Escherichia coli and Klebsiella pneumoniae strains. Second, it aims to determine the effect this association has on the ESBL enzymatic resistance mechanism. The synergistic action of AMX/1,8-cineole was evaluated using partial inhibitory concentrations (PIC), determined by a microplate, a checkerboard and time-kill assays. The effect of AMX/1,8-cineole associations on the ESBL enzymatic resistance mechanism was evaluated using a new optimized enzymatic assay. This assay was based on the determination of the AMX antibacterial activity when combined with 1,8-cineole (at subinhibitory concentrations) in the presence or absence of the ß-lactamase enzyme toward a sensitive E. coli strain. The results of both checkerboard and time-kill assays showed a strong synergistic action between AMX and 1,8-cineole. The results of the enzymatic assay showed that the combination of AMX with 1,8-cineole notably influences the enzymatic resistance of the reaction by decreasing the affinity of the β-lactam antibiotic, AMX, to the β-lactamase enzyme. All obtained results suggested that the AMX/1,8-cineole association could be employed in therapy to overcome bacterial resistance to AMX while reducing the prevalence of resistance.

Photocatalytic Cu2WS4 Nanocrystals for Efficient Bacterial Killing and Biofilm Disruption

Background

Bacterial biofilm-related wound infections threaten human health due to the lack of efficient treatments. Therefore, developing a novel strategy for wound infection care is urgently needed.

Methods

Cube-shaped Cu₂WS₄ nanocrystals (CWSNs) were successfully prepared via a microwave-assisted method. CWSNs, as photocatalysts, were first studied by using fluorescence spectroscopy for their ability to generate reactive oxygen species (ROS). The antibacterial and biofilm inhibition abilities of CWSNs were determined in vitro by using Staphylococcus aureus (S.aureus) as the model bacterium. Moreover, a CWSN gel was prepared and applied to treat S. aureus-infected wounds in mice. The toxicity of the CWSNs was evaluated through in vitro cell and in vivo animal experiments.

Results

Studies on the properties of the CWSNs demonstrated that these nanomaterials can catalyze the generation of hydroxyl radicals (•OH) without the addition of H₂O₂ after visible-light irradiation, indicating their photocatalytic ability. Moreover, the in vitro experimental results showed that the CWSNs not only adhered to the surfaces of S. aureus to kill the bacteria, but also inhibited S. aureus biofilm formation. The in vivo study showed that the CWSN gel produced excellent antibacterial effects against S. aureus infected wounds in mice and effectively promoted wound healing. Furthermore, toxicity tests showed that the CWSNs have negligible toxicity in vitro and in vivo.

Conclusion

This work provides a potential photocatalytic antibacterial nanoagent for efficient bacterial killing, inhibition of biofilms growth and wound infection treatment.