Antimicrobial activity and mode of action of terpene linalyl anthranilate against carbapenemase-producing Klebsiella pneumoniae

A Novel Dry-Cured Ham Broth-Derived Peptide JHBp2 Effectively Inhibits Salmonella typhimurium In Vitro: Integrated Metabolomic, Proteomic, and Molecular Simulation Analyses

JHBp2 is a peptide purified from Jinhua ham broth with antibacterial activity against Salmonella typhimurium. Untargeted metabolomics and label-free quantitative proteomics were used to analyze metabolic and protein expression changes in S. typhimurium after JHBp2 treatment. Cell wall and membrane damage results indicate that JHBp2 has membrane-disruptive properties, causing leakage of intracellular nucleic acids and proteins. Metabolomics revealed 516 differentially expressed metabolites, involving cofactor biosynthesis, purine metabolism, ABC transporters, glutathione metabolism, pyrimidine metabolism, etc. Proteomics detected 735 differentially expressed proteins, involving pyruvate metabolism, amino acid biosynthesis, purine metabolism, carbon metabolism, glycolysis/gluconeogenesis, etc. RT-qPCR and proteomics results showed a positive correlation, and molecular docking demonstrated stable binding of JHBp2 to some differentially expressed proteins. In summary, JHBp2 could disrupt the S. typhimurium cell wall and membrane structure, interfere with synthesis of membrane-related proteins, trigger intracellular substance leak, and reduce levels of enzymes and metabolites involved in energy metabolism, amino acid anabolism, and nucleotide anabolism.

Structure optimizing of flavonoids against both MRSA and VRE

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) cause more than 100,000 deaths each year, which need efficient and non-resistant antibacterial agents. SAR analysis of 162 flavonoids from the plant in this paper suggested that lipophilic group at C-3 was crucial, and then 63 novel flavonoid derivatives were designed and total synthesized. Among them, the most promising K15 displayed potent bactericidal activity against clinically isolated MRSA and VRE (MICs = 0.25-1.00 μg/mL) with low toxicity and high membrane selectivity. Moreover, mechanism insights revealed that K15 avoided resistance by disrupting biofilm and targeting the membrane, while vancomycin caused 256 times resistance against MRSA, and ampicillin caused 16 times resistance against VRE by the same 20 generations inducing. K15 eliminated residual bacteria in mice skin MRSA-infected model (>99 %) and abdominal VRE-infected model (>92 %), which was superior to vancomycin and ampicillin.

Comparative putative metabolites profiling of Tachypleus gigas and Carcinoscorpius rotundicauda hemocytes stimulated with lipopolysaccharide

Horseshoe crabs are among the most studied invertebrates due to their unique, innate immune system and biological processes. The metabolomics study was conducted on lipopolysaccharide (LPS)-stimulated and non-stimulated hemocytes isolated from the Malaysian Tachypleus gigas and Carcinoscorpius rotundicauda. LC-TOF-MS, multivariate analyses, principal component analysis (PCA), and partial least squares-discriminant analysis (PLS-DA) were included in this study to profile the metabolites. A total of 37 metabolites were identified to be differentially abundant and were selected based on VIP > 1. However, of the 37 putative metabolites, only 23 were found to be significant with ANOVA at p < 0.05. The metabolites were identified using several databases, and the literature review of the metabolites was reported in the manuscript. Thus, this study has provided further insights into the putative metabolites' presence in the hemocytes of horseshoe crabs that are stimulated and non-stimulated with LPS and their abundance in each species. Several putative metabolites showed they have medicinal values from previous studies.

In vitro antibacterial and anti-biofilm potential of an endophytic Schizophyllum commune

The emergence of antibiotic resistance in pathogens is one of the major health concerns facing mankind as different bacterial strains have developed resistance to antibiotics over the period of time due to overuse and misuse of antibiotics. Besides this, ability to form biofilms is another major factor contributing to antibiotic resistance, which has necessitated the need for exploration for novel and effective compounds with ability to inhibit biofilm formation. Endophytic fungi are reported to exhibit antibacterial and anti-biofilm potential and could serve as a potent source of novel antibacterial compounds. Majority of the bioactivities have been reported from fungi belonging to phylum Ascomycota. Endophytic basidiomycetes, inspite of their profound ability to serve as a source of bioactive compounds have not been exploited extensively. In present study, an attempt was made to assess the antibacterial, anti-biofilm and biofilm dispersion potential of an endophytic basidiomycetous fungus Schizophyllum commune procured from the culture collection of our lab. Ethyl acetate extract of S. commune showed good antibacterial activity against Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica and Vibrio cholerae. Minimum inhibitory concentration and minimum bactericidal concentration of the extract were in the range of 1.25-10 mg/ml against the tested bacterial pathogens. The mode of action was determined to be bactericidal which was further confirmed by time kill studies. Good anti-biofilm activity of S. commune extract was recorded against K. pneumoniae and S. enterica, which was further validated by fluorescence microscopy. The present study highlights the importance of endophytic basidiomycetes as source of therapeutic compounds.

PCR-Free, Label-Free, and Centrifugation-Free Diagnosis of Multiplex Antibiotic Resistance Genes by Combining mDNA-Au@Fe3O4 from Heating Dry and DNA Concatamers with G-Triplex

Accurate identification of antibiotic resistance genes (ARGs) is crucial for improving treatment and controlling the spread of antibiotic-resistant bacteria (ARB). Herein, a novel PCR-free, centrifugation-free, and label-free magnetic fluorescent biosensor (MFB) was developed by combining polyA-medium DNA-polyT (mDNA, which contained a partial sequence of a target DNA), gold nanoparticle (AuNP)-anchored magnetic nanoparticle (Au@Fe3O4), complementary strand DNA (CS) of the target DNA, DNA concatamer with G-triplex (G3), and thioflavin T (ThT). Thereinto, Au@Fe3O4 nanoparticles were first capped by mDNA strands within 20 min using a simple hot drying method, and then CS was added and hybridized with mDNA on Au@Fe3O4. Second, a DNA concatamer was used to bind with CS on Au@Fe3O4. When an ARG was present in the sample, the CS would recognize it and release the DNA concatamer into solution by a toehold-mediated strand displacement reaction. Finally, under magnetic separation, the free DNA concatamers with G3 were taken out easily and bound with ThT, resulting in strong fluorescence signals. The fluorescence intensity of ThT was positively correlated with the concentration of the ARG. The whole analysis was accomplished within 1.5 h using 96-well plates. Remarkably, our MFB was universal; eight ARGs were detected by replacing the corresponding mDNA and CS in this study. To verify the practicability of our method, 12 clinically isolated strains were analyzed. The results of the MFB method were in good agreement with those of the quantitative real-time PCR method with an area under the curve of 0.92 (95% confidence interval: 0.8479 to 0.9932), sensitivity of 92.00%, and specificity of 91.55%. Above all, the MFB assay established here is simple, low-cost, and universal and has great potential for applications in the identification of ARGs.

Monoterpene Thiols: Synthesis and Modifications for Obtaining Biologically Active Substances

Monoterpene thiols are one of the classes of natural flavors that impart the smell of citrus fruits, grape must and wine, black currants, and guava and are used as flavoring agents in the food and perfume industries. Synthetic monoterpene thiols have found an application in asymmetric synthesis as chiral auxiliaries, derivatizing agents, and ligands for metal complex catalysis and organocatalysts. Since monoterpenes and monoterpenoids are a renewable source, there are emerging trends to use monoterpene thiols as monomers for producing new types of green polymers. Monoterpene thioderivatives are also known to possess antioxidant, anticoagulant, antifungal, and antibacterial activity. The current review covers methods for the synthesis of acyclic, mono-, and bicyclic monoterpene thiols, as well as some investigations related to their usage for the preparation of the compounds with antimicrobial properties.

1,8-Cineol (Eucalyptol) Disrupts Membrane Integrity and Induces Oxidative Stress in Methicillin-Resistant Staphylococcus aureus

Due to the increased emergence of drug-resistant bacteria, the declining efficiency of traditional antimicrobials has generated severe concerns in recent years. Subsequently, more interest in other antimicrobial agents from natural resources draws more attention as an alternative to conventional medications. This study investigated the bactericidal mechanism of monoterpene 1,8-cineol (eucalyptol), a major compound of various essential oils, against methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial activity of 1,8-cineol was assessed by an MTT assay against clinical and reference MRSA strains. A cell membrane integrity test, followed by zeta potential (ZP) measurements, was performed to evaluate the disruption of the bacterial membrane integrity. Additionally, the cytotoxic effect of this molecule on MRSA bacteria was investigated by monitoring reactive oxygen species (ROS) generation, lipid peroxidation (MDA), and antioxidant enzyme activities (CAT and SOD). Regarding the anti-staphylococcal effect, the obtained results revealed the antibacterial efficacy of 1,8-cineol wherein the minimum inhibitory concentrations were equal to 7.23 mg/mL. Furthermore, it enhanced membrane permeability, with a 5.36-fold increase in nucleic acid and protein leakage as compared with untreated strains, along with the alteration of surface charge (ZP) in MRSA cells. The tested compound caused an increase in ROS generation reaching 17,462 FU and MDA production, reaching 9.56 μM/mg protein, in treated bacterial cells, along with a decrease in oxidative stress enzymes activities. Our findings suggest that 1,8-cineol has the ability to damage the membrane integrity and induce ROS-mediated oxidative stress in MRSA cells, leading to its antagonistic effect against this pathogen and consequently aiding in the reversal of antibiotic resistance.

Antibacterial Mechanism of Shikonin Against Vibrio vulnificus and Its Healing Potential on Infected Mice with Full-Thickness Excised Skin

Shikonin has anticancer, anti-inflammatory, and wound healing activities. Vibrio vulnificus is an important marine foodborne pathogen with a high fatality rate and rapid pathogenesis that can infect humans through ingestion and wounds. In this study, the antibacterial activity and possible antibacterial mechanism of shikonin against V. vulnificus were investigated. In addition, the ability of shikonin to control V. vulnificus infection in both pathways was assessed by artificially contaminated oysters and full-thickness excised skin-infected mice. Shikonin treatment can cause abnormal cell membrane function, as evidenced by hyperpolarization of the cell membrane, significant decreased intracellular ATP concentration (p < 0.05), significant increased intracellular reactive oxygen species and malondialdehyde content (p < 0.05), decreased cell membrane integrity, and changes in cell morphology. Shikonin at 40 and 80 μg/mL reduced bacterial numbers in shikonin-contaminated oysters by 3.58 and 2.18 log colony-forming unit (CFU)/mL. Shikonin can promote wound healing in mice infected with V. vulnificus by promoting the formation of granulation tissue, hair follicles, and sebaceous glands, promoting epithelial cell regeneration and epidermal growth factor production. These findings suggest that shikonin has a strong inactivation effect on V. vulnificus and can be used in food production and wound healing to effectively control V. vulnificus and reduce the number of diseases associated with it.

In Vitro and In Silico Evaluation of the Antimicrobial and Antioxidant Potential of Thymus pulegioides Essential Oil

The study was designed to analyze and evaluate the antioxidant and antibacterial properties of the essential oils of Thymus pulegioides L. grown in Western Romania. Thymus pulegioides L. essential oil (TPEO) was extracted by steam distillation (0.71% v/w) using a Craveiro-type apparatus. GC-MS investigation of the TPEO identified 39 different compounds, representing 98.46% of total oil. Findings revealed that thymol (22.89%) is the main compound of TPEO, followed by para-cymene (14.57%), thymol methyl ether (11.19%), isothymol methyl ether (10.45%), and beta-bisabolene (9.53%). The oil exhibits good antibacterial effects; C. parapsilosis, C. albicans, S. pyogenes, and S. aureus were the most sensitive strains. The antioxidant activity of TPEO was evaluated by peroxide and thiobarbituric acid value, 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), [2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium] (ABTS) radical scavenging assay, and beta-carotene/linoleic acid bleaching testing. The antioxidative data recorded reveal, for the first time, that TPEO inhibits primary and secondary oxidation products, in some particular conditions, better than butylated hydroxyanisole (BHA) with significant statistical difference (p < 0.05). Moreover, TPEO antioxidant capabilities in DPPH and ABTS assays outperformed alpha-tocopherol (p < 0.001) and delta-tocopherol (p < 0.001). Molecular docking analysis revealed that one potential target correlated with the TPEO antimicrobial activity was d-alanine-d-alanine ligase (DDl). The best scoring ligand, linalyl anthranilate, shared highly similar binding patterns with the DDl native inhibitor. Furthermore, molecular docking analysis also showed that the main constituents of TPEO are good candidates for xanthine oxidase and lipoxygenase inhibition, making the essential oil a valuable source for protein-targeted antioxidant compounds. Consequently, TPEO may represent a new potential source of antioxidant and antibacterial agents with applicability in the food and pharmaceutic industries.

Recent advances to combat ESKAPE pathogens with special reference to essential oils

Biofilm-associated bacteria, especially ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), are a serious challenge worldwide. Due to the lack of discovery of novel antibiotics, in the past two decades, it has become necessary to search for new antibiotics or to study synergy with the existing antibiotics so as to counter life-threatening infections. Nature-derived compounds/based products are more efficient than the chemically synthesized ones with less resistance and lower side effects. In this descriptive review, we discuss the most promising therapeutics for the treatment of ESKAPE-related biofilms. The first aspect includes different types of natural agents [botanical drugs, essential oils (EOs), antimicrobial peptides, bacteriophages, and endolysins] effective against ESKAPE pathogens. The second part of the review deals with special references to EOs/essential oil components (EOCs) (with some exclusive examples), mode of action (via interfering in the quorum-sensing pathways, disruption of biofilm and their inhibitory concentrations, expression of genes that are involved, other virulence factors), existing in literature so far. Moreover, different essential oils and their major constituents were critically discussed using in vivo models to target ESKAPE pathogens along with the studies involving existing antibiotics.

Synthesis and Antimicrobial Activity of Sulfenimines Based on Pinane Hydroxythiols

The widespread presence of multidrug-resistant pathogenic microorganisms challenges the development of novel chemotype antimicrobials, insensitive to microbial tools of resistance. To date, various monoterpenoids have been shown as potential antimicrobials. Among many classes of molecules with antimicrobial activity, terpenes and terpenoids are an attractive basis for the design of antimicrobials because of their low toxicity and availability for various modifications. In this work, we report on the synthesis of sulfenimines from chiral trifluoromethylated and non-fluorinated pinane-type thiols. Final compounds were obtained with yields of up to 81%. Among the 13 sulfenimines obtained, 3 compounds were able to repress the growth of both bacteria (S. aureus, both MSSA and MRSA; P. aeruginosa) and fungi (C. albicans) with an MIC of 8-32 µg/mL. Although compounds exhibited relatively high cytotoxicity (the therapeutic index of 3), their chemotype can be used as a starter point for the development of disinfectants and antiseptics for targeting multidrug-resistant pathogens.

Chloroform extracts of Atractylodes chinensis inhibit the adhesion and invasion of Salmonella typhimurium

There are 27 million cases of Salmonella Typhimurium (STM) reported worldwide annually, which have resulted in 217,000 deaths to date. Thus, there is an urgent requirement to develop novel antibacterial agents to target the multidrug-resistant strains of STM. We evaluated the inhibitory effect of the chloroform extracts of Atractylodes chinensis (Ac-CE) on the virulence of STM in vitro and develop it as a potential antibacterial agent. First, we determined the in vitro effects of Ac-CE on STM biofilm formation, and swimming, swarming, and adhesion to mucin. Further, we evaluated the effect of Ac-CE on the adhesion and invasion of STM at the gene level. Lastly, we evaluated the inhibitory effect of Ac-CE on STM infectivity at the cellular level. Ac-CE could attenuate both the adhesion and invasion abilities of STM in vitro. At the gene level, it could inhibit the expression of flagella, pilus, biofilm, SPI-1, and SPI-2 genes, which are related to the adhesion and invasion ability of STM in cells. Ac-CE significantly downregulated the expression of inflammatory cytokines and the TLR4/MyD88/NF-κB pathway in an STM infection cell model. It also significantly recovered the expression of intestinal barrier-related genes and proteins in intestinal cells that are damaged during STM infection. Ac-CE is effective as an antivirulence agent in alleviating STM infection. Although the main components of Ac-CE were analyzed.We have not demonstrated the antivirulence effect of the active ingredients in Ac-CE. And the antivirulence effect of Ac-CE and its active ingredients warrant further in vivo studies.

Anti- and Pro-Oxidant Properties of Essential Oils against Antimicrobial Resistance

The rapid evolution of antimicrobial resistance (AMR) has remained a major public health issue, reducing the efficacy of antibiotics and increasing the difficulty of treating infections. The discovery of novel antimicrobial agents is urgently needed to overcome the challenges created by AMR. Natural products such as plant extracts and essential oils (EOs) have been viewed as potential candidates to combat AMR due to their complex chemistry that carries inherent pro-oxidant and antioxidant properties. EOs and their constituents that hold pro-oxidant properties can induce oxidative stress by producing reactive oxygen species (ROS), leading to biological damage in target cells. In contrast, the antioxidant properties scavenge free radicals through offsetting ROS. Both pro-oxidant and antioxidant activities in EOs represent a promising strategy to tackle AMR. Thus, this review aimed to discuss how pro-oxidants and antioxidants in EOs may contribute to the mitigation of AMR and provided a detailed description of the challenges and limitations of utilizing them as a means to combat AMR.

Contribution of Aldehydes and Their Derivatives to Antimicrobial and Immunomodulatory Activities

Essential oils (EOs) are intricate combinations of evaporative compounds produced by aromatic plants and extracted by distillation or expression. EOs are natural secondary metabolites derived from plants and have been found to be useful in food and nutraceutical manufacturing, perfumery and cosmetics; they have also been found to alleviate the phenomenon of antimicrobial resistance (AMR) in addition to functioning as antibacterial and antifungal agents, balancing menstrual cycles and being efficacious as an immune system booster. Several main aldehyde constituents can be found in different types of EOs, and thus, aldehydes and their derivatives will be the main focus of this study with regard to their antimicrobial, antioxidative, anti-inflammatory and immunomodulatory effects. This brief study also explores the activity of aldehydes and their derivatives against pathogenic bacteria for future use in the clinical setting.

The Interference Mechanism of Basil Essential Oil on the Cell Membrane Barrier and Respiratory Metabolism of Listeria monocytogenes

In order to prevent food-borne diseases caused by Listeria monocytogenes (L. monocytogenes) safely and effectively, plant essential oils that have no toxic side effects and are not prone to drug resistance have become the focus of research. This article takes basil (Ocimum basilicum L.) essential oil (BEO) as the research object and explores its antibacterial mechanism against L. monocytogenes. The site of action was preliminarily determined to provide a theoretical basis for the development of natural antibacterial agents. The results show that BEO has good antibacterial activity against L. monocytogenes. After 8 h of treatment with BEO (1 mg/ml), the number of remaining bacteria reached an undetectable level. Combining spectroscopic analysis techniques (Raman, UV, and fluorescence spectroscopy) and fluorescence microscopy imaging techniques, it was found that BEO increased the disorder of the hydrocarbyl chain of phospholipid tail, which in turn led to increased cell membrane permeability, thereby causing the leakage of intracellular proteins and DNA. Meanwhile, respiratory metabolism experiments showed that BEO inhibited the EMP pathway by inhibiting the activity of key enzymes. From the molecular docking results, this inhibition may be attributed to the hydrophobic interaction between α-bergamotene and the amino acid residues of phosphofructokinase (PFK) and pyruvate kinase (PK). In addition, BEO can also cause oxidative stress, and reactive oxygen species (ROS) may also be related to the damage of cell membranes and enzymes related to respiratory metabolism.

Antibacterial Effect of Oregano Essential Oil against Vibrio vulnificus and Its Mechanism

Oregano essential oil (OEO) is an effective natural antibacterial agent, but its antibacterial activity against Vibrio vulnificus has not been widely studied. The aim of this study was to investigate the inhibitory effect and germicidal activity of OEO on V. vulnificus and its possible inhibition mechanism. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of OEO against four V. vulnificus strains (ATCC 27562 and three isolates from seafoods) were from 0.06 to 0.15 μL/mL. Compared with untreated bacteria, OEO reduced the concentration of intracellular adenosine triphosphate (ATP), hyperpolarized the cell membrane, increased the level of reactive oxygen species (ROS), and increased the concentration of intracellular malondialdehyde (MDA), but there was no obvious DNA damage at the OEO test concentration. It was indicated that OEO inactivated V. vulnificus by generating ROS which caused lipid peroxidation of cell membranes, thereby reducing the permeability and integrity of cell membranes and causing morphological changes to cells, but there was no obvious damage to DNA. In addition, OEO could effectively kill V. vulnificus in oysters at 25 °C, and the number of bacteria decreased by 48.2% after 0.09% OEO treatment for 10 h. The good inhibitory effect and bactericidal activity of OEO showed in this study, and the economy and security of OEO make it possible to apply OEO to control V. vulnificus contamination in oysters and other seafoods.

Antimicrobial activity and mode of action of 1,8-cineol against carbapenemase-producing Klebsiella pneumoniae

Antimicrobial resistance remains one of the most challenging issues that threatens the health of people around the world. Plant-derived natural compounds have received considerable attention for their potential role to mitigate antibiotic resistance. This study was carried out to assess the antimicrobial activity and mode of action of a monoterpene, 1,8-cineol (CN) against carbapenemase-producing Klebsiella pneumoniae (KPC-KP). Results showed that resazurin microplate assay and time-kill analysis revealed bactericidal effects of CN at 28.83 mg/mL. Zeta potential showed that CN increased the surface charge of bacteria and an increase of outer membrane permeability was also detected. CN was able to cause leakage of proteins and nucleic acids in KPC-KP cells upon exposure to CN and ethidium bromide influx/efflux experiment showed the uptake of ethidium bromide into the cell; this was attributed to membrane damage. CN was also found to induce oxidative stress in CN-treated KPC-KP cells through generation of reactive oxygen species which initiated lipid peroxidation and thus damaging the bacterial cell membrane. Scanning and transmission electron microscopies further confirmed the disruption of bacterial cell membrane and loss of intracellular materials. In this study, we demonstrated that CN induced oxidative stress and membrane damage resulting in KPC-KP cell death.

Chemical Composition and Biological Activities of the Essential Oils of Chrysophyllum albidum G. Don (African Star Apple)

The volatile compounds of the fruit and leaf essential oils of the African star fruit, Chrysophyllum albidum G. Don, were characterized by gas chromatography-mass spectrometry in this study. The antimicrobial, antibiofilm, and antioxidant activities of the essential oils were also investigated. Thirty-five and thirty-four compounds, representing 97.84% and 97.87%, were identified in the leaf and fruit essential oils, respectively. The antimicrobial activity of the oils was evaluated in vitro against eight pathogens using the broth microdilution method. The fruit essential oil exhibited broad-spectrum antimicrobial activity in the antimicrobial susceptibility test, with minimum inhibitory concentrations (MICs) ranging from 0.195 to 6.250 mg/mL, while the leaf essential oils showed antimicrobial activity with MICs in the range of 6.875–13.750 mg/mL. The antibiofilm activity was assessed via the crystal violet staining assay, with Pseudomonas aeruginosa as the model organism. The concentrations of the leaf and fruit essential oil required for half-maximal inhibition of biofilm formation (BIC₅₀) were 6.97 ± 0.56 and 4.78 ± 0.21 mg/mL, respectively. In evaluating antioxidant activity, the total antioxidant capacity obtained from the phosphomolybdenum assay was 104.8 ± 2.4 and 101.6 ± 0.8 μg/g AAE for leaf and fruit essential oils, respectively. The IC₅₀ values obtained from the hydrogen peroxide scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging, and inhibition of lipid peroxidation assays were 301.8 ± 0.7 and 669.2 ± 2.1 μg/mL, 1048.0 ± 0.3 and 1454.0 ± 0.3 μg/mL, and 460.1 ± 2.7 and 457.4 ± 0.3 μg/mL for both leaf and fruit essential oils, respectively. The results obtained in this study suggest that the leaf and fruit essential oil of Chrysophyllum albidum G. Don could find potential use in the food, cosmetic, and pharmaceutical industries as preservative and pharmaceutical agents.

Combination Therapy Involving Lavandula angustifolia and Its Derivatives in Exhibiting Antimicrobial Properties and Combatting Antimicrobial Resistance: Current Challenges and Future Prospects

Antimicrobial resistance (AMR) has been identified as one of the biggest health threats in the world. Current therapeutic options for common infections are markedly limited due to the emergence of multidrug resistant pathogens in the community and the hospitals. The role of different essential oils (EOs) and their derivatives in exhibiting antimicrobial properties has been widely elucidated with their respective mechanisms of action. Recently, there has been a heightened emphasis on lavender essential oil (LEO)’s antimicrobial properties and wound healing effects. However, to date, there has been no review published examining the antimicrobial benefits of lavender essential oil, specifically. Previous literature has shown that LEO and its constituents act synergistically with different antimicrobial agents to potentiate the antimicrobial activity. For the past decade, encapsulation of EOs with nanoparticles has been widely practiced due to increased antimicrobial effects and greater bioavailability as compared to non-encapsulated oils. Therefore, this review intends to provide an insight into the different aspects of antimicrobial activity exhibited by LEO and its constituents, discuss the synergistic effects displayed by combinatory therapy involving LEO, as well as to explore the significance of nano-encapsulation in boosting the antimicrobial effects of LEO; it is aimed that from the integration of these knowledge areas, combating AMR will be more than just a possibility.

An Overview of the Potential Therapeutic Applications of Essential Oils

The emergence of antimicrobial resistance (AMR) has urged researchers to explore therapeutic alternatives, one of which includes the use of natural plant products such as essential oils (EO). In fact, EO obtained from clove, oregano, thymus, cinnamon bark, rosemary, eucalyptus, and lavender have been shown to present significant inhibitory effects on bacteria, fungi, and viruses; many studies have been done to measure EO efficacy against microorganisms. The strategy of combinatory effects via conventional and non-conventional methods revealed that the combined effects of EO-EO or EO-antibiotic exhibit enhanced efficacy. This paper aims to review the antimicrobial effects of EO, modes of EO action (membrane disruption, efflux inhibition, increase membrane permeability, and decrease in intracellular ATP), and their compounds' potential as effective agents against bacteria, fungi, and viruses. It is hoped that the integration of EO applications in this work can be used to consider EO for future clinical applications.

The Antibacterial Agent Identified from Acidocella spp. in the Fluid of Nepenthes gracilis Against Multidrug-Resistant Klebsiella pneumoniae: A Functional Metagenomic Approach

Aims: The fluid of Nepenthes gracilis harbors diverse bacterial taxa that could serve as a gene pool for the discovery of the new genre of antimicrobial agents against multidrug-resistant Klebsiella pneumoniae. The aim of this study was to explore the presence of antibacterial genes in the fluids of N. gracilis growing in the wild. Methods: Using functional metagenomic approach, fosmid clones were isolated and screened for antibacterial activity against three strains of K. pneumoniae. A clone that exhibited the most potent antibacterial activity was sent for sequencing to identify the genes responsible for the observed activity. The secondary metabolites secreted by the selected clone was sequentially extracted using hexane, chloroform, and ethyl acetate. The chemical profiles of a clone (C6) hexane extract were determined by gas chromatography/mass spectrometry (GC-MS). Results: Fosmid clone C6 from the fluid of pitcher plant that exhibited antibacterial activity against three strains of K. pneumoniae was isolated using functional metagenome approach. A majority of the open reading frames detected from C6 were affiliated with the largely understudied Acidocella genus. Among them, the gene that encodes for coproporphyrinogen III oxidase in the heme biosynthesis pathway could be involved in the observed antibacterial activity. Based on the GC-MS analysis, the identities of the putative bioactive compounds were 2,5-di-tert-butylphenol and 1-ethyl-2-methyl cyclododecane. Conclusions: The gene that encodes for coproporphyrinogen III oxidase in the heme biosynthesis pathway as well as the secondary metabolites, namely 2,5-di-tert-butylphenol and 1-ethyl-2-methyl cyclododecane could be the potential antibacterial molecules responsible for the antibacterial activity of C6.