Antimicrobial Activity Of Essential Oils Research Articles

Synergistic antimicrobial activity of essential oils and oleoresins of cinnamon (Cinnamomum zeylanicum), clove bud (Syzygium aromaticum) and ginger (Zingiber officinale)

The essential oils (EOs) and oleoresins (ORs) of Cinnamomum zeylanicum (cinnamon) and Syzygium aromaticum (clove bud), and Zingiber officinale (ginger) are highly important for therapeutical benefits. This study targeted on the evaluation of the antimicrobial activity of extracted EOs and ORs of three spices and their mixtures against five bacteria and two fungi compared to some commercial antimicrobial agents. The agar-disk diffusion assay and minimum inhibitory concentration (MIC) were done for evaluation of antimicrobial activity and the checkboard assay was done using fractional inhibition concentration to determine the synergism and efficacy of the essential oil and oleoresin combinations. The extracted EOs and ORs comprised a mixture of different chemical compounds and exhibited different in-vitro antimicrobial activity. The cinnamon bark oil exhibited the highest inhibition zones compared to other EOs, ORs and positive controls. The EOs and ORs of cinnamon and clove bud are highly effective against Aspergillus niger and Candida albicans as they exhibited significantly lower MIC values than antifungal agents. Nevertheless, MIC values of five kinds of bacteria implied no significant difference between cinnamon bark oil, clove bud oil and antibiotics. It was proven that EOs are more active in inhibiting microorganisms than ORs.

Antioxidant and antimicrobial potential of essential oils of different types of pepper (Piper sp.)

Essential oils are mixtures of potent compounds with biological effects, such as those with antioxidant, antimicrobial, antitumor and/or anti-inflammatory effects. In this paper, the antioxidant and antimicrobial activity of essential oils of different types of commercial pepper was tested. Essential oils are prepared by hydrodistillation. Polyphenol content, reduction potential and DPPH radical inhibition were analyzed. Antimicrobial activity was tested on reference strains using the diffusion technique. The analysis showed that the essential oil of black pepper has a significantly higher antioxidant potential compared to the essential oils of green and white pepper. High antimicrobial activity was also found for the black pepper essential oil sample, except in the case of Pseudomonas aeruginosa.

Microbiological justification of the advisability of using essential oils of medicinal plants in the treatment of inflammatory diseases of the upper respiratory tract

Introduction. The role of the respiratory tract microflora violations as an etiological and pathogenetic factor in the development of the inflammative upper respiratory tract disease is indisputable, and the importance of persistence factors of respiratory opportunistic microorganisms (URT) is high. The traditional use of antibiotics and antimycotic agents in the pathology of URT has failed due to a significant increase in the number of antibiotic-resistant strains of microorganisms and the development of a number of undesirable adverse reactions in patients. An alternative advantage in these conditions is belonged to herbal preparations.Aim. To conduct a comparative in vitro study of antibacterial and antifungal activities of the plant essential oils as a component of the Dyshi Oil composition and the Dyshi Oil composition itself against opportunistic microorganisms - causative agents of inflammatory upper airway diseases.Materials and methods. Essential oils of clove, juniper, peppermint, eucalyptus, as well as the composition of oils “Dyshi” were used in the work. Staphylococcus aureus ATCC 25923, Klebsiella pneumoniae ICIS-278, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 24433 bacterial cultures were used as test cultures. Staphylococcus epidermidis 25 strain, isolated from a conditionally healthy person, was chosen as a representative of the URT normobiota. Antimicrobial activity of essential oils was determined by the method of diffusion in nutrient agar, MIC - by the method of serial dilutions.Results. The presence of zones of pronounced growth retardation of Staphylococcus aureus, Klebsiella and Pseudomonas, as well as yeast-like fungi was established when exposed to the composition of “Dyshi” oils, while separately used oils did not have a visible effect on the growth of bacteria and fungi, which indicates a synergistic interaction of the drug oils components.Conclusion. The presence of a synergistic antimicrobial effect of the “Dyshi” oil composition against opportunistic bacteria and yeast-like fungi of the genus Candida has been proven. The absence of an inhibitory effect on the growth of Staphylococcus epidermidis, which is a representative of the upper respiratory tract normobiota indicates a possible selective effect of “Dyshi” oil aimed at maintaining the colonization resistance of the URT biotope.

Taxonomic studies based on leaf epidermal microanatomy using high-resolution microscopy in Lamiaceous species and their antimicrobial effects.

The knowledge of essential oil antimicrobial activity of Lamiaceous species is assessed to describe its effects. The comprehensive foliar trichomes and stomatal morphology of the leaves of essential oil-bearing plants from the family Lamiaceae revealed diverse antimicrobial properties. The aim of this study was to investigate the foliar anatomical traits of 19 Lamiaceous taxa belonging to different tribes using light and scanning electron microscopy to correctly diagnose the species. The microanatomy of the foliar epidermis, trichomes diversity, and the stomatal apertural complex was visualized. Quantitative measurements were noted to describe the variations and the qualitative aspects for example, polygonal shape epidermal cells were examined. The stomatal aperture of four types and trichomes appendages both non-glandular and glandular was identified. Significant variation was found in both quantitative and qualitative traits, including unique ornamentation on the trichomes. The taxonomic key was constructed for accurate identification using qualitative morpho-structural traits. The outcomes of this research explored taxonomically to accurately identify the Lamiaceous species using anatomical characters. This study will provide provides the ecological adaptation linked to evolutionary traits of leaf surfaces that evolve with time to adapt the harsh environmental conditions. RESEARCH HIGHLIGHTS: Investigated foliar anatomical traits of 19 Lamiaceous species The anatomy and antimicrobial activity of essential oil yielding Lamiaceae species. SEM revealed diverse aspects including peculiar sculptured trichomes Microscopic identification of different stomatal complex.

Foeniculum vulgare Mill. ve Pimpinella anisum L. (Apiaceae) Türlerinin Uçucu Yağlarının Antimikrobiyal Aktivitesi

Today, essential oils are considered safe substances and can be used as antibacterial additives. Pimpinella anisum L. (Aniseed) and Foeniculum vulgare Mill. var. dulce (fennel) species are of great economic importance. It is among the medicinal and aromatic plants cultivated in wide areas in our country. In this study, it was aimed to determine the antimicrobial properties of essential oils obtained from Foeniculum vulgare Mill. and Pimpinella anisum L plants. The essential oils of the species were obtained by using the distillation method. The antimicrobial activities of essential oils by hand were studied using the hollow agar method. Known to be medically important in food, cosmetics and pharmaceutical products Enterobacter aerogenes (ATCC 13048), Enterococcus faecalis (ATCC 29212), Salmonella enteritidis (ATCC 13075), Staphylococcus aureus subsp. aureus (ATCC 25923), Escherichia coli (ATCC 25922) and Serratia marcescens (ATCC 13880) evaluated against pathogen and microbial contaminants. While Foeniculum vulgare showed results parallel to the antibiotic used as standard, no antibacterial activity was observed in Pimpinella anisum L.

Chemical composition and antimicrobial activity of essential oil obtained from the rhizomes of Kaempferia champasakensis: in vitro and molecular docking studies

Kaempferia champasakensis Picheans. & Koonterm (Zingiberaceae) is locally known as “Dia Lien hoa trang” in Vietnam. Despite a previous study on the essential oils (EO) of K. champasakensis leaves, no other studies have reported the chemical components and biological activities of K. champasakensis. Therefore, this study aims to identify the chemical constituents of the EO from the rhizomes of K. champasakensis and evaluate their antimicrobial activity, which has been re-confirmed through molecular docking studies. The gas chromatography-mass spectrometry (GC/MS) analysis revealed sixty-one constituents (95.4%) present in the EO of K. champasakensis rhizomes. Among them, camphene (40.7%), α-pinene (10.2%), and β-pinene (7.6%) were identified as the main compounds in the EO. Bioassays indicated its antimicrobial activity in the order of inhibitory effectiveness: Staphylococcus aureus > Enterococcus faecalis ≈ Candida albicans > Bacillus cereus ≈ Escherichia coli > Salmonella enterica > Pseudomonas aeruginosa. The molecular docking study of ligand-protein interactions involving the major constituents of EO was conducted against target proteins related to Staphylococcus aureus, Enterococcus faecalis, Candida albicans, Bacillus cereus, and Escherichia coli main activities. The results revealed that α-pinene exhibited strong binding affinity against E. coli, β-pinene demonstrated more effective inhibition against E. faecalis and B. cereus, and camphene primarily exhibited activity against C. albicans and S. aureus. Furthermore, the analysis of interactions between the main compounds and the selected proteins was elucidated in the current study. This is the first time that chemical components of the EO of K. champasakensis rhizomes and their antimicrobial activity have been reported. These findings contributed to the basis for further studies on the chemical compositions and biological effects of K. champasakensis.

Changes in essential oil composition of <i>Thymus vulgaris</i> under different storage conditions and its antimicrobial activity

Thyme (Thymus vulgaris L.) has been used for centuries in traditional medicine due to its various health benefits, and it is widely used today in aromatherapy, cosmetics, and even as a culinary herb. This study aimed to investigate how the chemical compositions and antimicrobial activity of essential oils extracted from the aerial parts of T. vulgaris were affected by storage at different temperatures. The essential oils were obtained by hydrodistillation of air-dried samples and analyzed using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The study observed changes in the essential oil’s composition when stored in a refrigerator (4 °C) and at room temperature (25 °C) for three months. The results revealed that the proportions of compounds with lower boiling temperatures such as β-myrcene (2.29–0.20%) and α-pinene (2.74–0.24%) along with γ-terpinene (7.84–4.81%) and p-cymene (10.93–5.61%) as thymol and carvacrol precursors, were significantly decreased when stored at room temperature. However, the amounts of thymol and carvacrol increased by 51.64 and 21.81%, respectively, after three months storage period, indicating a rise in the oil quality index. Storing the essential oil in a refrigerator resulted in minimal changes to the essential oil composition and maintained its primary quality. In addition, the antimicrobial activity of the essential oils was tested using the broth microdilution method and demonstrated that the essential oils from both storage methods retained their antimicrobial activity compared to freshly extracted ones. In summary, these findings are beneficial for essential oil producers and consumers in the pharmaceutical and cosmetic industries.

Chemical Compositions and Antimicrobial Activity of Essential Oils of Schisandra henryi subsp. hoatii from Vietnam

Chemical Compositions and Antimicrobial Activity of Essential Oils of Schisandra henryi subsp. hoatii from Vietnam

Antimicrobial activity of essential oils of Curcuma longa and Syzygium aromaticum against multiple drug-resistant pathogenic bacteria.

The present study was conducted to investigate the antimicrobial potential of essential oils of Curcuma longa and Syzygium aromaticum against multidrug-resistant pathogenic bacteria. Four identified bacterial isolates including Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii were selected and their antibiotic sensitivity was checked by disc diffusion assay. C. longa and S. aromaticum were subjected to steam distillation to obtain their essential oils. The crude essential oils were fractioned by employing column chromatography. Crude essential oils and their fractions were evaluated for their antibacterial activity by agar well diffusion assay and minimum inhibitory concentrations were calculated. All the selected bacterial isolates showed resistance to three or more than three antibiotic groups and were declared as multidrugresistant (MDRs). Crude essential oils of C. longa and S. aromaticum exhibited antimicrobial activity against all selected isolates but S. aromaticum activity was better than the C. longa with a maximum 19.3±1.50 mm zone of inhibition against A. baumannii at 1.04 µL/mL MIC. GC/MS analysis revealed the abundance of components including eugenol, eugenyl acetate, b- caryophyllene, and a- Humulene in both crude oil and fractions of S. aromaticum. While the main components of C. longa essential oil were Ar-tumerone, a-tumerone, b- Tumerone, I-Phellandrene, a-zingibirene, b- sesquiphellandrene, and p- Cymene. This study highlights that plant-based essential oils could be a promising alternative to antibiotics for which pathogens have developed resistance. C. longa and S. aromaticum carry compounds that have antimicrobial potential against multiple drug-resistant bacteria including MRSA. E. coli, K. pneumoniae and A. baumannii.

Antimicrobial activity of essential oils against Staphylococcus aureus and Staphylococcus chromogenes isolated from bovine mastitis.

Staphylococcus aureus and Staphylococcus chromogenes are pathogens frequently detected in bovine mastitis. Treatment and prevention of this disease have been usually carried on with antimicrobials. However, the emergence of bacterial isolates with antimicrobial resistance has aroused interest in new therapeutic alternatives. Plant essential oils (EOs) have been largely studied as antibacterial treatments. In the present study, EOs from five plants were evaluated for their antibacterial activities against S. aureus and S. chromogenes. Bacterial isolates were obtained in a previous study of clinical cases of bovine mastitis. EOs from lemongrass, eucalyptus, lavender, peppermint, and thyme were obtained by hydrodistillation and their chemical compositions were evaluated by gas chromatography (GC). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were evaluated for all EOs. The results demonstrated that citral (40.9%), myrcene (24.7%), and geraniol (1.9%) were detected in lemongrass EO; 1,8-cineole (76.9%), α-pinene (8.2%), and ledene (5.1%) in eucalyptus EO; 1,8-cineole (45.2%), camphor (18.2%), and fenchone (14.6%) in lavender EO; L-menthol (38.5%), menthofuran (16.3%), and citronellal (10.6%) in peppermint EO; and thymol (44.2%), p-cymene (24.6%) and 1,8-cineole (9.9%) in thyme EO. More effective antibacterial activities were observed only with the use of lemongrass (MIC and MBC ranging from 0.39 to 3.12mg/mL and 0.39 to 6.35mg/mL, respectively) and thyme (MIC and MBC ranging from 0.39 to 1.56mg/mL and 0.39 to 3.12mg/mL, respectively). Peppermint, lavender and eucalyptus EOs did not show bactericidal activities. In conclusion, lemongrass and thyme EOs are promising antibacterial alternatives against Staphylococcus species associated with bovine mastitis.

ACTIVITY OF PLANT ESSENTIAL OILS AGAINST OCHRATOXIN A PRODUCING ASPERGILLUS OCHRACEUS

Plant essential oils have been used in traditional medicines since ancient times to combat disease and in agro-food science to preserve food stuff. Antifungal activity of plant essential oils was evaluated using different substrates of varied moisture levels against ochratoxin A (OTA) producing Aspergillus ochraceus. A. ochraceus (n = 3) isolates were processed for antifungal activity of various essential oils including Zingiber officinale, Curcuma longa, Eucalyptus globulus, Syzygium aromaticum, Nigella sativa, Elettaria cardamomum, Cinnamomum verum and Cuminum cyminum extracted by hydro-distillation. To check the antimicrobial activity of essential oils, the highest zone of inhibition recorded was of C. verum (33.67±0.57mm) followed by S. aromaticum (30.33±0.57mm) and the least minimum inhibitory concentration (MIC) was of S. aromaticum (0.52±0.22 µg/mL) followed by C. verum (0.65±0.22 µg/mL). Antifungal activity was evaluated in term of log reduction and at the exposure time of 60 and 90 min, 6±0.00 log reduction was observed by S. aromaticum, C. verum and E. cardamomum with non-significant differences. At 15th, 30th, 45th and 60th day of experiment, toxin production by A. ochraceus at moisture contents (10, 20, 30, 40, 50, 60 and 70%) in un-inoculated groups and inoculated treated groups with C. verum Essential Oils were found non-significantly different to each other but significantly different from the OTA production in inoculated groups of wheat, maize and rice (intact and broken). At 10% moisture level, OTA production was low and reached to maximum level at 40% moisture level and again decline with increasing moisture level. Cinnamon has showed antifungal activity against A. ochraceus at all moisture levels. The confirmation of inhibition potential of C. verum was evaluated using thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC) techniques. This study illustrates that cinnamon oil is effective to inhibit the growth of OTA producing A. ochraceus in stored grains to overcome the economic losses. Keywords: Antifungal activity, Cinnamomum verum, Dimethyl sulfoxide, Log reduction, Minimum inhibitory concentration

Antimicrobial Activities of Essential Oils Extracted from the Leaf Materials of Selected Zingiberaceae Plants of Vizianagaram District, AP, India and Detection of Antimicrobial Compounds

Antimicrobial Activities of Essential Oils Extracted from the Leaf Materials of Selected Zingiberaceae Plants of Vizianagaram District, AP, India and Detection of Antimicrobial Compounds

Phytochemistry and Biological Activities of Essential Oils from Satureja calamintha Nepeta

Satureja calamintha nepeta (S. calamintha) has a history of successful use in the treatment of bacterial and fungal diseases. The present study was designed to investigate the chemical composition and antioxidant and antimicrobial activities of essential oils extracted from wild S. calamintha (EOSS) and domesticated S. calamintha (EOSD) for comparison purposes. Hydrodistillation was used to extract the essential oils (EOs), while GC/MS was used for chemical analysis. Antioxidant activity was studied using DPPH and FRAP assays. Antifungal activity was performed against Candida albicans, Aspergillus niger, Aspergillus flavus, and Fusarium oxysporum), while antibacterial activity was tested against clinically resistant bacteria, namely Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Proteus mirabilis. By using ab=n in silico approach, the antioxidant and antimicrobial activities of the main compounds of EOSS and EOSD were also investigated. The yields obtained of EOSS and EOSD were 2.80% and 1.95%, respectively, with a dominance of eucalyptol, pulegone and rotundifolone. Concerning the antioxidant power, the IC50 values recorded by the use of the DPPH assay were in the range of 23.03 ± 4.30 and 24.09 ± 4.38 μg/mL for EOSS and EOSD, respectively, while by using the FRAP assay, the EC50 values were in the range of 55.38 ± 2.16 and 60.72 ± 7.71 μg/mL for EOSS and EOSD, respectively. Importantly, both essential oils of EOSS and EOSD exhibited good antibacterial activity against all studied bacteria; notably, the inhibition zone ranged from 14 ± 0.00 to 48.67 ± 1.15 mm and the MICs ranged from 0.37 ± 0.00 to 5.96 ± 0.00 µg/mL. Similarly, the studied EOs showed important antifungal activities compared to all the studied fungi, wherein the inhibition percentage ranged from 47.33 ± 1.15 to 89.18 ± 0.75%, while the MICs ranged from 0.18 ± 0.00 to 2.98 ± 0.00 µg/mL. The molecular docking results showed that piperitenone and pulegone strongly inhibited human acetylcholinesterase, whereas (+)-Isomenthone and piperitenone strongly inhibited S. aureus nucleoside diphosphate kinase, and E. coli beta-ketoacyl-[acyl carrier protein] synthase, respectively. The outcome of this article suggests that EOs of S. calamintha can be developed as alternative agents to manage drug-resistant phenomena and free radical issues.

P44 | Antimicrobial activity of essential oils extracted from Origanum vulgare and Melaleuca armillaris against Escherichia coli isolated from poultry feces

Journal of Veterinary Pharmacology and TherapeuticsVolume 46, Issue S1 p. 106-107 POSTER PRESENTATIONS P44 | Antimicrobial activity of essential oils extracted from Origanum vulgare and Melaleuca armillaris against Escherichia coli isolated from poultry feces First published: 11 June 2023 https://doi.org/10.1111/jvp.13323Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume46, IssueS1Special Issue: 15th International Congress of the European Association for Veterinary Pharmacology and Toxicology held Bruges, Belgium, July 2–5, 2023June 2023Pages 106-107 RelatedInformation

Chemical composition, antioxidant, and antimicrobial activities of P. roxburghii oleoresin essential oils extracted by steam distillation, superheated steam, and supercritical fluid CO2 extraction.

Pinus roxburghii is a rich source of high-quality oleoresin that is composed of resin acids and essential oil (EO). The present research work was planned to study and compare the yield, biological activities, and chemical profiling of P. roxburghii oleoresin EOs extracted through various green extraction methods. Steam distillation (SD), supercritical fluid extraction, and superheated SD (SHSD) at different temperatures (120, 140, and 160°C) were employed to extract EOs from P. roxburghii oleoresin. Antioxidant potential of EOs was determined by total antioxidant content/ferric-reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH)-free radical scavenging activity (DPPH-FRSA), hydrogen peroxide scavenging assays, and percentage inhibition in linoleic acid. Antimicrobial activity of EOs was determined by resazurin microtiter-plate, disc diffusion, and micro-dilution broth susceptibility assays. Gas chromatography-mass spectrometry was used to determine the chemical composition of EOs. It was observed that extraction methods significantly affected the yield, biological activities, and chemical composition of EOs. The maximum yield (19.92%) was found in EO extracted by SHSD at 160°C. EO extracted by SHSD at 120°C showed the highest DPPH-FRSA (63.33%±0.47%), linoleic acid oxidation inhibition (96.55%±1.71%), hydrogen peroxide scavenging activity (59.42%±0.32%), and total antioxidant contents/FRAP (134.49%±1.34mg/L of gallic acid equivalent). The antimicrobial activity results showed that superheated steam-extracted EO of 120°C revealed the highest antifungal and antibacterial activity. It is concluded that SHSD is an alternative and effective technique for the extraction of oleoresins EO that improves the EO yield and biological activities. Further research on optimization and experimental parameters for the extraction of P. roxburghii oleoresin EO by SHSD is required.

Virtual screening of antimicrobial plant extracts by machine-learning classification of chemical compounds in semantic space.

Plant extract is a mixture of diverse phytochemicals, and considered as an important resource for drug discovery. However, large-scale exploration of the bioactive extracts has been hindered by various obstacles until now. In this research, we have introduced and evaluated a new computational screening strategy that classifies bioactive compounds and plants in semantic space generated by word embedding algorithm. The classifier showed good performance in binary (presence/absence of bioactivity) classification for both compounds and plant genera. Furthermore, the strategy led to the discovery of antimicrobial activity of essential oils from Lindera triloba and Cinnamomum sieboldii against Staphylococcus aureus. The results of this study indicate that machine-learning classification in semantic space can be a highly efficient approach for exploring bioactive plant extracts.

Antimicrobial activity and constituents of the leaf essential oil of Syzygium petelotii Merr. & Perry and Syzygium syzygioides (Miq.) Merr. & Perry from Vietnam

Syzygium plants are known as sources of biologically active substances. The essential oils constituents and antimicrobial activity of Syzygium petelotii Merr. & Perry and Syzygium syzygioides (Miq.) Merr. & Perry from Vietnam are being reported. Essential oils were obtained by hydrodistillation of the leaves of S. petelotii and S. syzygioides collected from Pù Hoạt Nature Reserve, Vietnam. The constituents of the essential oils were determined by using gas chromatography (GC) and gas chromatography-mass (GC/MS) spectrometry methods. The antimicrobial activity was evaluated by microdilution broth susceptibility assay. The results indicate that γ-guaiene (24.1%), β-caryphyllene (9.3%), α-pinene (7.8%), and β-pinene (6.1%) were the major compounds of S. petelotii. The main constituents of S. syzygioides were caryophyllene oxide (14.8%), α-pinene (10.6%), β-pinene (6.6%) and spathulenol (6.4%). The essential oil of S. petelotii showed pronounced antimicrobial activity against Pseudomonas aeruginosa ATCC27853 and Enterococcus faecalis ATCC299212, with minimum inhibitory concentration (MIC) values of 16.0 μg/mL and 64.0 μg/mL, respectively. The essential oil of S. syzygioides only displayed activity towards Pseudomonas aeruginosa ATCC27853 with MIC value of 32.0 μg/mL. Both essential oils exhibited antimicrobial activity towards Bacillus cereus ATCC14579 (MIC value, 128.0 μg/mL), and anti-candidal action against Candida albicans ATCC10231 with MIC value of 64.0 μg/mL. The chemical compositions and antimicrobial activity of essential oils of S. petelotii and S. syzygioides are being reported for the first time.

Chemical profile and antibacterial activity of essential oil from ironwood (Eusideroxylon zwageri) sawdust

The current study describes for the first time the chemical compositions and antimicrobial activity of essential oils from ironwood sawdust (Eusideroxylon zwageri) obtained from Borneo Island. Fifteen terpene metabolites were identified by GC-MS of the ironwood sawdust essential oil extracted by steam distillation. (E)-β-Caryophyllene was the oil’s major compound (35.81 ± 0.25%), while its oxygenated derivative (caryophyllene oxide, 8.78 ± 0.08%) was the third biggest terpene. α-Copaene (13.05 ± 0.02%) was also observed in a significant amount together with other minor sesquiterpene hydrocarbons and oxygenated sesquiterpenes. The oil also exhibited antibacterial activities against Gram-positive Multi-Drug Resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli (strain ESBL) during a disc diffusion assay with inhibition zones of 6.13 ± 0.03 mm and 3.35 ± 0.05 mm, respectively.

The antimicrobial efficacy of native Australian essential oils in liquid and vapour phase against foodborne pathogens and spoilage microorganisms

Foodborne pathogens and spoilage microorganisms are a source of concern for public health and the food industry. Considering the problem of antimicrobial resistance in microbes, controlling these microorganisms using synthetic antimicrobials is challenging, thus, essential oils are a potential natural alternative. Previous studies have predominantly focussed on the antimicrobial activity of essential oils in the liquid phase. However, in this work we report on the in vitro antimicrobial activity of the liquid and vapour phases of essential oils from native Australian plants Tasmanian mountain pepper (Tasmannia lanceolata), lemon myrtle (Backhousia citriodora), as well as the common herb thyme (Thymus vulgaris) against 11 common food spoilage and pathogenic bacteria and fungi. Initial screening was conducted using the disc diffusion assay. The minimum inhibitory concentration (MIC) of the oils was determined using the broth microdilution assay. The vapour phase antimicrobial activity of the oils was assessed using an inverted petri plate assay and the vapour phase MIC (V-MIC) was quantified using a vapour diffusion assay. GC-MS was adopted to elucidate the compositional profile of the oil in liquid phase. Two extraction methods, namely solid-phase microextraction (HS-SPME) and gas tight syringe headspace sampling (HS) coupled with GC-MS were used for profiling the composition of the volatiles. The findings of this study confirmed the antimicrobial activity of the oils in both liquid and vapour phases, with lemon myrtle and thyme generally showing stronger antimicrobial activity than Tasmanian mountain pepper. The activity in liquid phase was generally higher than the volatiles. However, lemon myrtle and Tasmanian mountain pepper berry volatiles were more effective against Aspergillus niger and Saccharomyces cerevisiae, respectively, relative to the liquid phase highlighting their potential as vapour phase antifungals. In the liquid and gas phases, the major compounds in lemon myrtle were Z-citral (neral) and E-citral (geranial). Polygodial and thymol were the major compounds in Tasmanian mountain pepper and thyme in the liquid phase, respectively. However, the main compounds in their volatiles were p-cymene and γ-terpinene. In conclusion, our research indicates the essential oils' potent vapour phase activity, highlighting their potential application in gaseous diffusion-dependent food applications such as active antimicrobial food packaging.

Activity of plant essential oils against clinically and environmentally isolatedSalmonella entericaserotypes:in vitroassays and molecular docking

This research aimed to evaluate the antimicrobial activity of essential oils (EOs) against clinically and environmentally isolated Salmonella serotypes. Oregano, thyme, and grapefruit EO compounds were identified, and the antimicrobial activity was evaluated against the S. Saintpaul, Oranienburg, and Infantis serotypes. In addition, molecular docking was performed to explore the possible mechanisms between compounds of EOs with microbial enzymes. Thymol was the main compound identified in oregano (44.0%) and thyme (31%) EOs, while d-limonene was present in a greater proportion in grapefruit EO. Oregano EO had the highest antimicrobial activity, followed by thyme and grapefruit EOs. Oregano and thyme EOs illustrated a greater inhibitory capacity to all serotypes, particularly with the environmental S. Saintpaul. Oregano EO presented values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration of 0.1 μL/mL for all serotypes, while thyme and grapefruit EOs presented MIC values of 0.1 μL/mL for the clinical serotypes S. Infantis and S. Oranienburg, respectively. Molecular docking analysis showed the optimal binding free energies for thymol and carvacrol with glucokinase, ATP-dependent-6-fructokinase, outer membrane porin C, and topoisomerase IV. Our results indicate that these EOs can inhibit clinically and environmentally isolated Salmonella serotypes and can be used as alternatives for developing natural food preservatives.