Rapid bark-mediated tree stem methane transport occurs independently of the transpiration stream in Melaleuca quinquenervia.

Tree stem methane emissions are important components of lowland forest methane budgets. The potential for species-specific behaviour among co-occurring lowland trees with contrasting bark characteristics has not been investigated. We compare bark-mediated methane transport in two common lowland species of contrasting bark characteristics (Melaleuca quinquenervia featuring spongy/layered bark with longitudinally continuous airspaces and Casuarina glauca featuring hard/dense common bark) through several manipulative experiments. First, the progressive cutting through M. quinquenervia bark layers caused exponential increases in methane fluxes (c. 3 orders of magnitude); however, sapwood-only fluxes were lower, suggesting that upward/axial methane transport occurs between bark layers. Second, concentrated methane pulse-injections into exposed M. quinquenervia bark, revealed rapid axial methane transport rates (1.42 mm s-1 ), which were further supported through laboratory-simulated experiments (1.41 mm s-1 ). Laboratory-simulated radial CH4 diffusion rates (through bark) were c. 20-times slower. Finally, girdling M. quinquenervia stems caused a near-instantaneous decrease in methane flux immediately above the cut. By contrast, girdling C. glauca displayed persistent, though diminished, methane fluxes. Overall, the experiments revealed evidence for rapid 'between-bark' methane transport independent from the transpiration stream in M. quinquenervia, which facilitates diffusive axial transport from the rhizosphere and/or sapwood sources. This contrasts with the slower, radial 'through-bark' diffusive-dominated gas transportation in C. glauca.

Identification of MYB gene family in medicinal tea tree Melaleuca alternifolia (Maiden and Betche) cheel and analysis of members regulating terpene biosynthesis.

BACKGROUND: The tea tree (Melaleuca alternifolia) is renowned for its production of tea tree oil, an essential oil primarily composed of terpenes extracted from its shoot. MYB transcription factors, which are one of the largest TF families, play a crucial role in regulating primary and secondary metabolite synthesis. However, knowledge of the MYB gene family in M. alternifolia is limited. METHODS AND RESULTS: Here, we conducted a comprehensive genome-wide analysis of MYB genes in M. alternifolia, referred to as MaMYBs, including phylogenetic relationships, structures, promoter regions, and GO annotations. Our findings classified 219 MaMYBs into four subfamilies: one 5R-MYB, four 3R-MYBs, sixty-one MYB-related, and the remaining 153 are all 2R-MYBs. Seven genes (MYB189, MYB146, MYB44, MYB29, MYB175, MYB162, and MYB160) were linked to terpenoid synthesis based on GO annotation. Phylogenetic analysis with Arabidopsis homologous MYB genes suggested that MYB193 and MYB163 may also be involved in terpenoid synthesis. Additionally, through correlation analysis of gene expression and metabolite content, we identified 42 MYB genes associated with metabolite content. CONCLUSION: The results provide valuable insights into the importance of MYB transcription factors in essential oil production in M. alternifolia. These findings lay the groundwork for a better understanding of the MYB regulatory network and the development of novel strategies to enhance essential oil synthesis in M. alternifolia.

A synergistic anti-bacterial and anti-adhesion activity of tea tree (Melaleuca alternifolia) and lemon eucalyptus tree (Eucalyptus citriodora Hook) essential oils on Legionella pneumophila.

Legionella pneumophila is a Gram-negative bacterial pathogen that colonizes natural and artificial water systems and has the ability to form a biofilm. The biofilm protects L. pneumophila from various environmental factors and makes it more resistant to chlorine-based disinfectants. This study investigated the anti-bacterial properties of tea tree (Melaleuca alternifolia (Maiden and Betche) Cheel) oil and lemon eucalyptus tree (Eucalyptus citriodora Hook) essential oils (EOs) and their synergistic, additive inhibitory and anti-adhesive effects against L. pneumophila biofilm formation on polystyrene. The minimum effective concentration (MEC) for tea tree is 12.8 mg ml-1 and for lemon eucalyptus tree EO 6.4 mg ml-1. In the checkerboard assay, different combinations of these two EO show synergistic and additive anti-microbial activity. The minimum anti-adhesive concentration (MAC) for tea tree is 12.8 mg ml-1 and for lemon eucalyptus tree EO 6.4 mg ml-1. A combination of 3.2 mg ml-1 tea tree EO and 0.8 mg ml-1 lemon eucalyptus tree EO showed the strongest anti-adhesive effect against L. pneumophila on polystyrene. The tested oils and their combination showed intriguing potential to inhibit L. pneumophila biofilm formation.

A terpene synthase supergene locus determines chemotype in Melaleuca alternifolia (tea tree).

Leaf oil terpenes vary categorically in many plant populations, leading to discrete phenotypes of adaptive and economic significance, but for most species, a genetic explanation for the concerted fluctuation in terpene chemistry remains unresolved. To uncover the genetic architecture underlying multi-component terpene chemotypes in Melaleuca alternifolia (tea tree), a genome-wide association study was undertaken for 148 individuals representing all six recognised chemotypes. A number of single nucleotide polymorphisms in a genomic region of c. 400 kb explained large proportions of the variation in key monoterpenes of tea tree oil. The region contained a cluster of 10 monoterpene synthase genes, including four genes predicted to encode synthases for 1,8-cineole, terpinolene, and the terpinen-4-ol precursor, sabinene hydrate. Chemotype-dependent null alleles at some sites suggested structural variants within this gene cluster, providing a possible basis for linkage disequilibrium in this region. Genotyping in a separate domesticated population revealed that all alleles surrounding this gene cluster were fixed after artificial selection for a single chemotype. These observations indicate that a supergene accounts for chemotypes in M. alternifolia. A genetic model with three haplotypes, encompassing the four characterised monoterpene synthase genes, explained the six terpene chemotypes, and was consistent with available biparental cross-segregation data.

Draft genome of the medicinal tea tree Melaleuca alternifolia.

BACKGROUND: Melaleuca alternifolia is a commercially important medicinal tea tree native to Australia. Tea tree oil, the essential oil distilled from its branches and leaves, has broad-spectrum germicidal activity and is highly valued in the pharmaceutical and cosmetic industries. Thus, the study of genome, which can provide reference for the investigation of genes involved in terpinen-4-ol biosynthesis, is quite crucial for improving the productivity of Tea tree oil. METHODS AND RESULTS: In our study, the next-generation sequencing was used to investigate the whole genome of Melaleuca alternifolia. About 114 Gb high quality sequence data were obtained and assembled into 1,838,159 scafolds with an N50 length of 1021 bp. The assembled genome size is about 595 Mb, twice of that predicted by flow cytometer (300 Mb) and k-mer analysis (345 Mb). Benchmarking Universal Single-Copy Orthologs analyses indicated that only 11.3% of the conserved single-copy genes were miss. Repetitive regions cover over 40.43% of the genome. A total of 44,369 protein-coding genes were predicted and annotated against Nr, Swissprot, Refseq, COG, KOG, and KEGG database. Among these genes, 32,909 and 16,241 genes were functionally annotated in Nr and KEGG, respectively. Moreover, 29,411 and 14,435 genes were functionally annotated in COG and KOG. Additionally, 457,661 simple sequence repeats and 1109 transcription factors (TFs) form 67 TF families were identified in the assembled genome. CONCLUSION: Our findings provide a draft genome sequencing of M. alternifolia which can act as a reference for the deep sequencing strategies, and are useful for future functional and comparative genomics analyses.

Optimizing the Antimicrobial Synergism of Melaleuca alternifolia (Tea Tree) Essential Oil Combinations for Application against Respiratory Related Pathogens.

Antimicrobial research into the use of Melaleuca alternifolia essential oil has demonstrated broad-spectrum activity; however, much of the research published focuses on identifying the potential of this essential oil individually, rather than in combination for an enhanced antimicrobial effect. This study aimed to determine the antimicrobial activity of four essential oil combinations, all inclusive of M. alternifolia, against nine pathogens associated with the respiratory tract. The minimum inhibitory concentration assay was used to determine the antimicrobial activity of four essential oil combinations, M. alternifolia in combination with Cupressus sempervirens, Origanum majorana, Myrtus communis, and Origanum vulgare essential oils. The interactions between essential oil combinations were analyzed using isobolograms and SynergyFinder 2.0 software to visualize the synergistic potential at varied ratios. The antimicrobial activity of the different combinations of essential oils all demonstrated the ability to produce an enhanced antimicrobial effect compared to the essential oils when investigated independently. The findings of this study determined that isobolograms provide a more in-depth analysis of an essential oil combination interaction; however, the value of that interaction should be further quantified using computational modelling such as SynergyFinder. This study further supports the need for more studies where varied ratios of essential oils are investigated for antimicrobial potential.

Comparison of chitosan and SLN nano-delivery systems for antibacterial effect of tea tree (Melaleuca alternifolia) oil against P. aeruginosa and S. aureus.

Treatment of wounds is challenging due to bacterial infections, including Staphylococcus aureus and Pseudomonas aeruginosa. Using the merits of alternative antimicrobials like tea tree oil (TTO) and nanotechnology, they can be helpful in combatting bacterial infections. Solid lipid nanoparticle (SLN) and chitosan (CS) nanoparticles show great potential as carriers for enhancing the stability and therapeutic benefits of oils. The aim of this study is to compare the influence of nanocarriers in enhancing the antibacterial effects of TTO. The study evaluates the physicochemical and antibacterial properties of TTO-SLN and TTO-CS against P. aeruginosa and S. aureus. The TTO-SLN nanoparticles showed a clear round shape with the average diameter size of 477 nm, while the TTO-CS nanoparticles illustrated very homogeneous morphology with 144 nm size. The encapsulation efficiency for TTO-CS and TTO-SLN was ∼88.3% and 73.5%, respectively. Minimum inhibitory concentration against S. aureus and P. aeruginosa for TTO-CS, TTO-SLN, and pure TTO were 35 and 45 µg ml-1, 130 and 170 µg ml-1, and 380 and 410 µg ml-1, respectively. Since TTO-CS revealed an impressively higher antimicrobial effects in comparison with TTO-SLN and TTO alone, it can be considered as a nanocarrier that produces the same antimicrobial effects with lower required amounts of the active substance.

Safety assessment and adverse drug reaction reporting of tea tree oil (Melaleuca aetheroleum).

Tea tree (Melaleuca alternifolia) essential oil is widely used as an antiseptic. It mainly consists of monoterpenes with terpinen-4-ol as the major constituent. The aim of this study was to review literature on safety data about tea tree oil and to assess its safety by investigating 159 cases of adverse reactions possibly caused by the oil, reported to the World Health Organization (WHO) from December 1987 until September 2021. To extract these data, VigiBase, the WHO global database of individual case safety reports maintained by the Uppsala Monitoring Centre (UMC), was used. All cases were categorized and analysed and 16 serious cases further assessed. It was concluded that tea tree oil should never be administered orally, as it can lead to central nervous system depression and pneumonitis. Applied topically, skin disorders may occur, especially when the oil had been exposed to light or air. This yields monoterpene oxidation products, being potent skin irritants. Tea tree oil stored under appropriate conditions and not exceeding the expiration date should be considered safe to use by non-vulnerable people for non-serious inflammatory skin conditions, although the occurrence of adverse reactions such as contact allergies is difficult to predict.

HPTLC Analysis and Chemical Composition of Selected Melaleuca Essential Oils.

Tea tree oil (TTO) is a volatile essential oil obtained by distillation, mainly from the Australian native plant Melaleuca alternifolia (Maiden & Betche) Cheel (Myrtaceae). In this study, a comparative analysis of the chemical constituents of seven tea tree oils (M. alternifolia) and four other Melaleuca spp. oils (M. cajuputi, (MCa), two chemotypes of M. quinquenervia, (MNe and MNi), and M. ericifolia (MRo)) was carried out using gas chromatography-mass spectrometry (GC-MS) and high-performance thin-layer chromatography (HPTLC). Among the seven TTOs, terpinen-4-ol (37.66-44.28%), γ-terpinene (16.42-20.75%), α-terpinene (3.47-12.62%), α-terpineol (3.11-4.66%), and terpinolene (2.75-4.19%) were the most abundant compounds. On the other hand, the most abundant compounds of the other Melaleuca oils varied, such as 1,8-cineole (64.63%) in MCa oil, (E)-nerolidol (48.40%) and linalool (33.30%) in MNe oil, 1,8-cineole (52.20%) in MNi oil, and linalool (38.19%) and 1,8-cineole (27.57%) in MRo oil. HPTLC fingerprinting of Melaleuca oils enabled the discrimination of TTO oils from other Melaleuca spp. oils. Variation was observed in the profile of the Rf values among EOs. The present study shows that HPTLC is one of the best ways to identify and evaluate the quality control in authenticating TTOs, other Melaleuca EOs, or EOs from other species within the Myrtaceae.

Effects of Melaleuca alternifolia Chell (Tea Tree) and Eucalyptus globulus Labill. Essential Oils on Antibiotic-Resistant Bacterial Biofilms.

In the present investigation, the anti-biofilm potential of two essential oils (EOs), Melaleuca alternifolia Chell (Tea-Tree) (TTO) and Eucalyptus globulus Labill. (EEO) was characterized and tested "in vitro" against both mature biofilms and biofilms in the process of formation, produced by strains belonging to three main categories of antibiotic resistant bacteria (ARB): Vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA) and broad-spectrum ß-lactamase-producing Escherichia coli (ESBL). The study was carried out in 96-well microtiter-plates using EOs alone, in association with each other and in combination with antibiotics against both single and multi-species biofilm. The study demonstrated the ability of TTO and EEO to counteract the ARB strains in sessile form, with promising results in particular against the biofilm in formation. Mature biofilm by ESBL E. coli was the most sensitive in the results from the quantification study of viable cells performed in multi-species biofilms. Lastly, in all tests, carried out using TTO/EEO associations and EOs/antibiotic combinations, the synergistic effect which emerged from the FIC-index has been confirmed, and both the reduction of biofilm in formation, and the removal of mature structure was obtained at very low concentrations, with values from 4 to >512-fold lower than the minimum inhibitory concentration (MIC) of the single compounds.

Antifungal Potential of Melaleuca alternifolia against Fungal Pathogen Fusarium oxysporum f. sp. cubense Tropical Race 4.

Fusarium wilt of bananas caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4) poses the most serious threat to banana production globally. The disease has been managed using chemical fungicides, yet the control levels are still unsatisfactory. This study investigated the antifungal activities of tea tree (Melaleuca alternifolia) essential oil (TTO) and hydrosol (TTH) against Foc TR4 and their bioactive components. The potential of TTO and TTH in inhibiting the growth of Foc TR4 was evaluated in vitro using agar well diffusion and spore germination assays. Compared to the chemical fungicide, TTO effectively suppressed the mycelial growth of Foc TR4 at 69%. Both the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of TTO and TTH were established at 0.2 µg/µL and 50% v/v, respectively, suggesting the fungicidal nature of the plant extracts. The disease control efficacies were also demonstrated by a (p ≤ 0.05) delayed Fusarium wilt symptom development in the susceptible banana plants with reduced LSI dan RDI scores from 70% to around 20-30%. A GC/MS analysis of TTO identified terpinen-4-ol, eucalyptol, and α-terpineol as the major components. In contrast, an LC/MS analysis of TTH identified different compounds, including dihydro-jasmonic acid and methyl ester. Our findings indicate the potential of tea tree extracts as natural alternatives to chemical fungicides to control Foc TR4.

Dietary tea tree (Melaleuca alternifolia) essential oil as alternative to antibiotics alleviates experimentally induced Eimeria tenella challenge in Japanese quails.

Coccidiosis is one of the most common infectious diseases seen in Japanese quails. The current study was conducted to evaluate the impact of tea tree essential oil (TTEO) on growth performance and intestinal health of quails in response to Eimeria tenella challenge. A total of 250 Japanese quails were divided into five treatments: untreated uninfected (negative control); untreated infected (positive control); infected + Amprolium; infected and 1% TTEO; infected and 2% TTEO. Except negative control, all groups were orally dosed with 5 × 104 sporulated oocysts of E. tenella. The results revealed that supplementation of 1% TTEO and treatment of amprolium improved feed intake, weight gain and feed conversion ratio in infected quails compared to the positive control. Similarly, lesion score and mortality was significantly (p < 0.01) reduced in quails supplemented with 2% TTEO and amprolium treated birds. Moreover, oocysts counts and histological features of caecum in infected birds were reversed in 1% TTEO and amprolium treatment. The histological findings of amprolium and 1% TTEO supplemented quails showed intact intestinal villi with mild sloughed epithelium. In conclusion, 1% TTEO can be safely used to control coccidiosis in Japanese quails as natural effective compound.

Utilizing intramammary Melaleuca alternifolia as an organic internal sealant for dry-off therapy in Murrah buffaloes.

The effects of intramammary dry cow therapy based on the administration of 5% Melaleuca alternifolia tea tree essential oil (TTO) as an internal teat sealant to Murrah cows were evaluated. A longitudinal prospective and retrospective negative control study was performed using 12 buffaloes from a total of 20 Murrah buffaloes on an organic farm, with the cow used as a control for herself. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for treatments with pure oil (TTO) and medication containing 5% TTO (O5) were determined. The buffaloes were clinically examined, and the teats were evaluated using thermography and ultrasound. Udder health was monitored during the first 100 days in milk (DIM) using milk somatic cell count (SCC) and California mastitis test (CMT). Laboratory tests against standard strains Staphylococcus aureus ATCC®25,923™, Escherichia coli ATCC®25,922™, and wild bacterial strains showed maximum MIC values of 50 µL/mL for the TTO and O5 treatments. One wild-type S. aureus strain showed no MBC. No adverse effects were observed after the intramammary application of TTO. The CMT and SCC values were similar (P > 0.05) for all observations. The medication containing 5% TTO was effective in vitro and compatible with the intramammary tissue in vivo of Murrah buffaloes. TTO was safe, not inducing inflammatory processes or other modifications of the teat detectable by thermography or ultrasound. It was able to protect buffaloes during the dry period under field conditions, demonstrating potential use as a teat sealant for organic farms.

Antimicrobial effects of Melaleuca alternifolia (tea tree) essential oil against biofilm-forming multidrug-resistant cystic fibrosis-associated Pseudomonas aeruginosa as a single agent and in combination with commonly nebulized antibiotics.

Broth microdilution assays were used to determine minimum inhibitory concentrations (MICs) and fractional inhibitory concentration indices (FICIs) of tea tree oil (TTO), tobramycin, colistin and aztreonam (ATM) against clinical cystic fibrosis-associated Pseudomonas aeruginosa (CFPA) isolates (n = 20). The minimum biofilm eradication concentration (MBEC) and fractional biofilm eradication concentration index (FBECI) were also determined using a similar microbroth dilution checkerboard assay, with biofilms formed using the MBEC device® . TTO was effective at lower concentrations against multidrug-resistant (MDR) CFPA isolates (n = 3) in a biofilm compared to in a planktonic state (MBEC 18·7-fold lower than MIC). CFPA within biofilm was less susceptible to ATM, colistin and tobramycin compared to planktonic cells (MBEC 6·3-fold, 9·3-fold, and 2·1-fold higher than MIC respectively). All combinations of essential oil and antibiotic showed indifferent relationships (FICI 0·52-1·72) when tested against planktonic MDR CFPA isolates (n = 5). Against CFPA isolates (n = 3) in biofilm, combinations of TTO/aztreonam and TTO/colistin showed indifferent relationships (mean FBECI 0·85 and 0·60 respectively), whereas TTO/tobramycin showed a synergistic relationship (mean FBECI 0·42). The antibiofilm properties of TTO and the synergistic relationship seen between TTO and tobramycin against CFPA in vitro make inhaled TTO a promising candidate as a potential therapeutic agent.

Isolation and Identification of Acylphloroglucinols in the Medicinal Plant, Melaleuca alternifolia (Australian Tea Tree).

Melaleuca alternifolia (tea tree), family Myrtaceae, is endemic to the northern rivers of NSW, Australia. Since 1925, the volatile components of the hydro- and steam-distilled oils of the leaves have been studied in detail. However, the less-volatile compounds have not been investigated. Using an ethanolic extract of the seedling leaves, the non-volatile components were studied using gas chromatography-mass spectrometry (GC/MS) and liquid chromatography- mass spectrometry (LC/MS). Four of these less-volatile components were isolated by preparative-HPLC from young seedling leaves and identified as the acylphloroglucinols 1-(2,6-dihydroxy-4-methoxy-3-methylphenyl)-2-methylpropan-1-one, callisalignone A, 1-(2,6-dihydroxy-4-methoxyphenyl)-3-methylbutan-1-one and pulverulentone B described here for the first time from M. alternifolia. These compounds change in concentration in the leaf sets as later seedling leaves mature on the seedling.

Design, Synthesis, and Bioactivity of Eighteen Novel 2H-1,4-Benzoxazin-3(4H)-one Containing a Propanolamine Moiety.

To develop a novel skeleton for broad-spectrum pesticides with high-efficiency against tea tree diseases, a series of aniline 2H-1,4-benzoxazin-3(4H)-one derivatives containing a propanolamine structure was synthesized and confirmed by 1 H-NMR, 13 C-NMR, 19 F-NMR, HRMS, and single-crystal diffraction analysis. Bioactivities were evaluated against tobacco mosaic virus (TMV, the model virus), three kinds of bacteria, and five typical plant fungi. Bioassay results showed that compound 2i (EC50 =395.05 µg/mL) had the best curative activity against TMV, 3d (EC50 =45.70 µg/mL) had the best inhibitory activity against Pseudomonas syringae pv. Actinidiae, and 3a (EC50 =13.53 µg/mL) had the best inhibitory activity against Pestalotiopsis trachicarpicola. Scanning electron microscope morphological observation of P. trachicarpicola treated with 0, 100, and 200 µg/mL 3a revealed dried, flattened and folded outer walls of the hyphae at higher concentrations, leading to inhibition of fungal growth. The broad-spectrum bioactivities (against viruses, bacteria and fungi) of this series of target compounds indicate that these 2H-1,4-benzoxazin-3(4H)-one derivatives containing a propanolamine moiety are potential skeletons for developing pesticides with wide-ranging activities against various tea tree diseases.

Extraction of essential oils from tea tree (Melaleuca alternifolia) and lemon grass (Cymbopogon citratus) using betaine-based deep eutectic solvent (DES).

INTRODUCTION: The essential oils of tea tree (Melaleuca alternifolia) leaves mainly contain eucalyptol, α-terpinene, γ -terpinene, and terpinen-4-ol and have anti-bacterial, anti-fungal, anti-infective, and anti-inflammatory actions. The essential oils of lemon grass (Cymbopogon citratus) leaves mainly contain neral, geranial, and geraniol and have anti-microbial and anti-fungal activities and hypocholesterolemic effect. OBJECTIVES: The present study describes the use of low-toxicity solvents called betaine-based deep eutectic solvents (DESs) for efficient extraction of essential oils from tea tree and lemon grass. H2 O and EtOH were used for extraction as control methods. METHODOLOGY: Quantitative analysis was performed using gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring mode. Scanning electron micrography (SEM) and antioxidant assays for extracted samples were also conducted. RESULTS: The results indicated that extraction for tea tree using betaine/sucrose (molar ratio 2:1) improved the yields of terpinolene and eucalyptol 2.5- and 1.9-fold, respectively, compared with the control method. In lemon grass, extraction using betaine/sucrose (molar ratio 2:1) improved the yields of neral and geranial 1.9- and 1.7-fold, respectively, compared with the control method. CONCLUSION: These results demonstrated the effective extraction of essential oils from plant leaves under milder conditions than those needed for the conventional methods. The environmentally benign DESs for the extraction would be applicable to the food and cosmetic industries.

Ultrastructural Damages to H1N1 Influenza Virus Caused by Vapor Essential Oils.

Influenza viruses are transmitted from human to human via airborne droplets and can be transferred through contaminated environmental surfaces. Some works have demonstrated the efficacy of essential oils (EOs) as antimicrobial and antiviral agents, but most of them examined the liquid phases, which are generally toxic for oral applications. In our study, we describe the antiviral activity of Citrus bergamia, Melaleuca alternifolia, Illicium verum and Eucalyptus globulus vapor EOs against influenza virus type A. In the vapor phase, C. bergamia and M. alternifolia strongly reduced viral cytopathic effect without exerting any cytotoxicity. The E. globulus vapor EO reduced viral infection by 78% with no cytotoxicity, while I. verum was not effective. Furthermore, we characterized the EOs and their vapor phase by the head-space gas chromatography-mass spectrometry technique, observing that the major component found in each liquid EO is the same one of the corresponding vapor phases, with the exception of M. alternifolia. To deepen the mechanism of action, the morphological integrity of virus particles was checked by negative staining transmission electron microscopy, showing that they interfere with the lipid bilayer of the viral envelope, leading to the decomposition of membranes. We speculated that the most abundant components of the vapor EOs might directly interfere with influenza virus envelope structures or mask viral structures important for early steps of viral infection.

Potential Use of Tea Tree Oil as a Disinfectant Agent against Coronaviruses: A Combined Experimental and Simulation Study.

The COVID-19 pandemic has highlighted the relevance of proper disinfection procedures and renewed interest in developing novel disinfectant materials as a preventive strategy to limit SARS-CoV-2 contamination. Given its widely known antibacterial, antifungal, and antiviral properties, Melaleuca alternifolia essential oil, also named Tea tree oil (TTO), is recognized as a potential effective and safe natural disinfectant agent. In particular, the proposed antiviral activity of TTO involves the inhibition of viral entry and fusion, interfering with the structural dynamics of the membrane and with the protein envelope components. In this study, for the first time, we demonstrated the virucidal effects of TTO against the feline coronavirus (FCoVII) and the human coronavirus OC43 (HCoV-OC43), both used as surrogate models for SARS-CoV-2. Then, to atomistically uncover the possible effects exerted by TTO compounds on the outer surface of the SARS-CoV-2 virion, we performed Gaussian accelerated Molecular Dynamics simulations of a SARS-CoV-2 envelope portion, including a complete model of the Spike glycoprotein in the absence or presence of the three main TTO compounds (terpinen-4-ol, γ-terpinene, and 1,8-cineole). The obtained results allowed us to hypothesize the mechanism of action of TTO and its possible use as an anti-coronavirus disinfectant agent.

Assessment of Chemical Composition and Anti-Penicillium Activity of Vapours of Essential Oils from Abies Alba and Two Melaleuca Species in Food Model Systems.

The possibilities of the practical utilization of essential oils (EOs) from various plant species in the food industry have attracted the attention of the scientific community. Following our previous studies, the antifungal activities of three further commercial EOs, Melaleuca armillaris subsp. armillaris (rosalina; REO), Melaleuca quinquenervia (niaouli; NEO), and Abies alba (fir; FEO), were evaluated in the present research in respect to their chemical profiles, over four different concentrations, 62.5 µL/L, 125 µL/L, 250 µL/L, and 500 µL/L. The findings revealed that the major compounds of REO, NEO, and FEO were linalool (47.5%), 1,8-cineole (40.8%), and α-pinene (25.2%), respectively. In vitro antifungal determinations showed that the inhibition zones of a Penicillium spp. mycelial growth ranged from no inhibitory effectiveness (00.00 ± 00.00 mm) to 16.00 ± 1.00 mm, indicating a very strong antifungal activity which was detected against P. citrinum after the highest REO concentration exposure. Furthermore, the in situ antifungal efficacy of all EOs investigated was shown to be dose-dependent. In this sense, we have found that the highest concentration (500 µL/L) of REO, NEO, and FEO significantly reduced (p < 0.05) the growth of all Penicillium strains inoculated on the bread, carrot, and potato models. These results indicate that the investigated EOs may be promising innovative agents in order to extend the shelf life of different types of food products, such as bread, carrot and potato.