Disc Volatilization Method Research Articles

In Situ Antimicrobial Properties of Sabinene Hydrate, a Secondary Plant Metabolite.

The objective of this research was to investigate natural products for their potential against pathogenic microorganisms. Sabinene hydrate (SH), a monoterpenoid, is synthesised by numerous different plants as a secondary metabolite. At present, there is a lack of definite investigations regarding the antimicrobial activity of SH itself and its different isomers. The antimicrobial effects of commercially available SH (composed mainly of trans-isomer) were evaluated within a range of concentrations in three types of contact tests: solid and vapor diffusion and the macro-broth dilution method. Moreover, the effects of SH on the rate of linear growth and spore germination were also examined. Ethanolic SH solutions were tested against an array of microorganisms, including blue-stain fungi (Ceratocystis polonica, Ophiostoma bicolor, O. penicillatum), frequently originating from bark beetle galleries; three fungal strains (Musicillium theobromae, Plectosphaerella cucumerina, and Trichoderma sp.) isolated from a sapwood underneath bark beetle galleries (Ips typographus) on spruce (Picea abies) stems; Verticillium fungicola, isolated from diseased I. typographus larvae; two Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus), two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa); five yeasts (Candida albicans, C. krusei, C. parapsilosis, Saccharomyces cerevisiae, and Rhodotorula muscilaginosa), and two saprophytic fungi (Aspergillus niger and Penicillium notatum). In solid agar disc diffusion tests, Gram-positive bacteria exhibited greater susceptibility to SH than Gram-negative bacteria, followed by yeasts and fungi. The most resistant to SH in both the disc diffusion and broth macro-dilution methods were P. aeruginosa, A. niger, and Trichoderma sp. strains. Blue-stain fungi and fungi isolated from the Picea sapwood were the most resistant among the fungal strains tested. The minimum inhibition concentrations (MICs) generated by SH and determined using a disc volatilization method were dependent on the fungal species and played an important role in the development of microorganism inhibition. The two Gram-positive bacteria, B. subtilis and S. aureus (whose MICs were 0.0312 and 0.0625 mg/mL, respectively), were the organisms most susceptible to SH, followed by the Gram-negative bacterium, E. coli (MIC = 0.125 mg/mL) and two yeasts, C. albicans and C. kruei (MIC was 0.125 mg/mL and 0.25 mg/mL, respectively). C. parapsilosis (MIC = 0.75 mg/mL) was the yeast most resistant to SH. The investigation of antimicrobial properties of plant secondary metabolites is important for the development of a new generation of fungicides.

Systematic analysis of antimicrobial activity, phytochemistry, and in silico molecular interaction of selected essential oils and their formulations from different Indian spices against foodborne bacteria

Essential oils (EOs) from Indian spices like Elettaria cardamomum (L.) Maton (small green cardamom), Syzygium aromaticum (L.) Merr. & L.M. Perry (clove), Cinnamomum zeylanicum Blume (cinnamon quills), and Cinnamomum tamala (Buch.-Ham.) T. Nees & C. H. Eberm (Indian bay leaves) exhibit a broad spectrum range of biological activity including antibacterial and antifungal activity. Yet, there is a lack of data regarding the antimicrobial activity of their formulations. Also, the link between the antimicrobial effect of individual EO with their chemical composition and molecular interaction with bacterial pathogens has not been systematically explored. Therefore, the objectives of the current study were to evaluate the antimicrobial activity and phytochemical characterization of EOs and to bridge the gap between them through in-silico molecular interactions. The antibacterial activity of EOs of four different spices and their formulations against foodborne pathogens such as Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa was evaluated using the disc volatilization method. The chemical profile of the individual EO was determined through GC-MS analysis and molecular interactions of identified major components with bacterial proteins were carried out through molecular docking studies. All EOs and their formulations exhibited antibacterial activity ranging from 5.92 to 24.55 mm and 11–23.52 mm, respectively. Among all EOs, cinnamon and formulation C (cardamom: cinnamon- 2:1) exhibited the highest antibacterial activity. The composition of the EOs included sesquiterpenes, monoterpenoids, monoterpenes, and, phenylpropanoids such as (E)-cinnamaldehyde, δ-cadinene, α-copaene, eugenol, caryophyllene, eugenol acetate, methyl eugenol, menthadiene, eucalyptol, α-terpinyl acetate, and sabinene. Furthermore, docking study revealed that the abundant compounds from cinnamon EO mainly α-copaene and δ-cadinene had a high binding affinity towards the bacterial essential proteins which increases the bacterial susceptibility towards cinnamon EO. The selected EOs and their formulations were systematically analysed and they were effective against foodborne pathogens. The current findings suggest the application of these EOs against food pathogens with further research.

Comparison between the Antimicrobial Activity of Essential Oils and Their Components in the Vapor Phase against Food-related Bacteria.

In this study, the antibacterial properties of the volatile components of four essential oils (cinnamon, clove, origanum, and peppermint oil) and five of their components (allyl isothiocyanate (AITC), carvacrol, citral, eugenol, and (+)-limonene) against five food-related bacteria (Escherichia coli, Listeria monocytogenes, Salmonella Typhimurium, Pseudomonas fluorescens, and Enterococcus faecalis) were evaluated. The results of disc volatilization method revealed that AITC exhibited antibacterial activity against the five tested strains at the lowest concentration, as did cinnamon oil and carvacrol. Moreover, the total aerobic bacterial count in coleslaw salad was suppressed in all test groups treated with AITC compared to that in control.

Inhibition of Fungal Strains Isolated from Cereal Grains via Vapor Phase of Essential Oils.

Fungal contamination in stored food grains is a global concern and affects food economics and human and animal health. It is clear that there is a need to develop new technologies with improved performances that are also eco-friendly in nature. Due to the bioactivity of essential oils (EOs) in the vapor phase, their low toxicity for humans, and their biodegradability and antifungal properties, EOs could be a suitable solution. In this study, we explored the potential of thyme, oregano, lemongrass, clove, and cajeput EOs in the vapor phase. For 17 days, inhibitory activity was assessed against five strains of postharvest pathogens—Aspergillus spp., Fusarium s. l. spp., and Penicillium ochrochloron—isolated from cereal grains. A modified disc volatilization method was used, which is more effective in comparison to traditional screening methods. Three concentrations were tested (250, 125, and 62.5 μL/L). The two highest concentrations resulted in complete inhibition of fungal growth; however, even 62.5 μL/L showed a significant antifungal effect. The efficiency of EOs followed this order: thyme > oregano > lemongrass > clove > cajeput. From our findings, it appears that the use of EOs vapors is a better option not only for laboratory experiments, but for subsequent practice.

In vitro and in silico evaluation of antifungal activity of cassia (Cinnamomum cassia) and holy basil (Ocimum tenuiflorum) essential oils for the control of anthracnose and crown-rot postharvest diseases of banana fruits

Anthracnose and crown-rot postharvest diseases of banana fruit are responsible for major postharvest losses of the fruit. For natural control of these diseases, in vitro antifungal activity of cassia and holy basil essential oils was evaluated by disc volatilization method. Cassia essential oil at 6 μL per plate exhibited 100% growth inhibition of both the causative fungal pathogens, namely Colletotrichum musae and Lasiodiplodia theobromae. Holy basil essential oil was capable of completely inhibiting the growth of L. theobromae at 6 μL per plate, whereas it could inhibit C. musae up to 96% at 10 μL per plate. Molecular docking and conceptual DFT studies have been performed to ascertain the components of essential oils responsible for antifungal activity based on their binding affinities to chitin synthase protein and chemical behaviour. Components, such as eugenol, cinnamyl acetate, caryophyllene, humulene and trans-calamenene, may most likely be responsible for high activity of the tested essential oils as per the in silico results.

The Novel Quantitative Assay for Measuring the Antibiofilm Activity of Volatile Compounds (AntiBioVol)

Herein, we present a new test, dubbed AntiBioVol, to be used for the quantitative evaluation of antibiofilm activity of volatile compounds in vitro. AntiBioVol is performed in two 24-well plates using a basic microbiological laboratory equipment. To demonstrate AntiBioVol usability, we have scrutinized the activity of volatilized eucalyptus, tea tree, thyme essential oils, and ethanol (used for method suitability testing) against biofilms of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. We have also compared AntiBioVol with the standard disc volatilization method, placing a special stress on evaluating the impact of various technical parameters on the outcomes of the latter method. The obtained results indicate that AntiBioVol allows analyzing the antibiofilm activity of volatile compounds in a high number of repeats and provides semi-quantitative or quantitative results of high repeatability. In comparison to disc volatilization, AntiBioVol is a more space- and cost-effective method that allows analyzing various types of microbial aggregates. Moreover, we have indicated that the possible reasons for the discrepancies in the results obtained by means of the standard disc volatilization method may be related to various parameters of the testing dishes used (height, volume, diameter) and to various volumes of the agar medium applied. In turn, the application of a 24-well plate and a strictly defined AntiBioVol protocol provide a higher control of experimental conditions. Therefore, the application of AntiBioVol may enable an optimization of and introduction of volatile compounds to the fight against infective biofilms.

Effect of Essential Oils and GRAS Compounds on Postharvest Disease Control in Mango (Mangifera indica L.cv Tom EJC)

Purpose : Mango (Mangifera indica L. cv. Tom EJC) has a high economic value due to its unique qualities. Postharvest diseases such as anthracnose cause considerable loss of fruits in the market. Applications of synthetic fungicides are the common practice for controlling postharvest diseases, which could lead to hazardous effects on health. Therefore, search for alternative measures for the control of anthracnose are in demand. Research Method : Different fungal species have been described as causative agents of above disease. To determine the causative agent, fungal isolations were done from symptomatic fruits and identified by morphological and molecular techniques. Sodium bicarbonate, and sodium metabisulphite were used as GRAS (Generally Recognized as Safe) compounds and clove, cinnamon and citronella oils were used as essential oils during in-vitro studies to evaluate their potential to control the pathogen. The mycelial inhibitory capacity of five concentrations (1µLplate-1- 5µLplate-1) of each essential oil was evaluated in-vitro disc volatilization method. Compounds with minimum inhibitory concentrations were selected for in-vivo studies. Essential oil treatments for mango comprised of fumigation and application of GRAS compounds by dipping 15 and 30 minute time intervals. Physiochemical properties (pH, titrable acidity and total soluble solid content) of treated and non-treated mango fruits were evaluated.Findings : The identified causative agent of anthracnose was Colletotrichum siamense. Sodium bicarbonate (80000ppm), sodium metabisulphite (1500ppm) showed 100% inhibition of radial mycelia growth against the pathogen through in-vitro poison food method.100% inhibition of radial mycelia growth was reported with clove and cinnamon oil at all the concentrations tested (1-5µLplate-1). The citronella oil showed the lowest inhibitory activity. 15 minute and 30 minute dipping in sodium bicarbonate and fumigation with clove oil and cinnamon oil treatments effectively controlled anthracnose disease in mango, in comparison to the recommended fungicide Chlorothalonil (3mL/L). Physiochemical properties of mango were not altered by any of the treatments in comparison to no-treated fruits.Originality / Value : These results suggest that Sodium bicarbonate, Clove oil and Cinnamon oil could be used as alternatives to control the anthracnose disease in mango.

The antifungal activity of essential oils in combination with warm air flow against postharvest phytopathogenic fungi in apples

Essential oils (EOs) are strong plant-derived antimicrobials. For their efficient use in the agri-food industry, the problems with technology of their application have to be solved. In vitro antifungal activity of cinnamon, oregano, lemongrass and clove essential oils (EOs) was tested by innovative method using EO in combination with warm air flow (WAF). EOs in concentrations from 0.25 to 512 μL/L of air were tested against eleven phytopathogenic fungi. Application of EOs in concentration of 4 and 16 μL/L by WAF method was used for treatment of apples inoculated with Penicillium expansum. Detailed sensory analysis of treated apples was performed. The WAF was more effective compare to standard disc volatilization method (DVM), the average minimum inhibitory concentrations in vitro were 5.6 μL/L during 5 min WAF treatment, compared to 136 μL/L during the DVM 24 h treatment. EOs applied by WAF delayed the incidence and development of P. expansum on apples with minimal adverse effect on their sensory profile. The WAF treatment could be considered for the development of antifungal treatments in the agri-food industry.

Essential oil of Algerian Eucalyptus citriodora: Chemical composition, antifungal activity

Essential oil of Eucalyptus citriodora is a natural product which has been attributed for various medicinal uses. In the present investigation, E.citriodora essential oil was used to evaluate its antifungal effect against medically important dermatophytes. Essential oil from the Algerian E.citriodora leaves was analyzed by GC and GC/MS. The antifungal effect of E.citriodora essential oil was evaluated against four dermatophytes: Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes, Trichophyton rubrum using disc diffusion method, disc volatilization method, and agar dilution method. The chemical composition of the oil revealed the presence of 22compounds accounting for 95.27% of the oil. The dominant compounds were citronellal (69.77%), citronellol (10.63%) and isopulegol (4.66%). The disc diffusion method, MIC and MFC determination, indicated that E.citriodora essential oil had a higher antifungal potential against the tested strains with inhibition zone diameter which varied from (12 to 90mm) and MIC and MFC values ranged from (0.6 to 5μL/mL and 1.25 to 5μL/mL) respectively. The M.gypseum was the most resistant to the oil. The results of the present study indicated that E.citriodora essential oil may be used as a new antifungal agent recommended by the pharmaceutical industries.

Modelling the effect of essential oil of betel leaf (Piper betle L.) on germination, growth, and apparent lag time of Penicillium expansum on semi-synthetic media

The current study aimed at characterizing the chemical components of betel leaf (Piper betle L. var. Tamluk Mitha) essential oil (BLEO) and modelling its effect on growth of Penicillium expansum on semi-synthetic medium. Gas chromatography-mass spectrophotometry (GC-MS) analysis of BLEO revealed the presence of different bioactive phenolic compounds in significant amounts. Among 46 different components identified, chavibetol (22.0%), estragole (15.8%), β-cubebene (13.6%), chavicol (11.8%), and caryophyllene (11.3%) were found to be the major compounds of BLEO. A disc diffusion and disc volatilization method were used to evaluate antifungal activity of the oil against a selected food spoilage mould. The logistic model was used to study the kinetics of spore germination. Prediction and validation of antifungal effect of BLEO was performed on semi-synthetic medium (apple juice agar) using predictive microbiological tools. The Baranyi and Roberts model was used to estimate maximum growth rate (μmax in mm/day) and apparent lag time (λ in days) of the mould. Secondary modelling was performed using a re-parameterized Monod-type equation based on cardinal values to study the effect of different BLEO concentration on estimated growth parameters. Emax (minimum concentration of oil at which mould growth was inhibited) and MIC (minimum inhibitory concentration of BLEO at which lag time is infinite) value of BLEO against P. expansum was estimated to be 0.56 and 0.74μl/ml, respectively, which was found to be similar on potato dextrose agar (PDA) as well as apple juice agar (AJA) medium. The correlation between estimated growth parameters of the mould on both the media was obtained with satisfactory statistical indices (R2 and RMSE). This study revealed inhibitory efficacy of BLEO on spore germination, mycelial growth and apparent lag time of P. expansum in a dose-dependent manner. Hence, BLEO has potential to be used as a natural food preservative.

Antibacterial activities of isothiocyanates (ITCs) extracted from horseradish (Armoracia rusticana) root in liquid and vapor phases against 5 dominant bacteria isolated from low-salt Jeotgal, a Korean salted and fermented seafood

Antibacterial activities of isothiocyanates (ITCs) extracted from horseradish (Armoracia rusticana) root in liquid and vapor phases were evaluated against 5 dominant bacteria (2 strains of Bacillus sp., Straphylococcus sp., Streptococcus sp., and Enterobacter sp.) from jeotgal. ITCs in liquid and vapor phases exhibited potent antibacterial activities based on a disc diffusion method (liquid phase) and a disc volatilization method (vapor phase). ITCs minimum bactericidal concentrations in the liquid phase (broth dilution method) and vapor phase (disc volatilization method) ranged from 0.208±0.091 to 2.083±0.722 mg/mL and 0.078±0.000 to 1.875±0.722 mg/mL, respectively. ITCs in the vapor phase showed stronger antibacterial activities against all tested bacterial strains. ITCs extracted from horseradish root in the vapor phase can be used as a natural preservative to extend the shelf-life of jeotgal.

Preservative effectiveness of essential oils in vapor phase combined with modified atmosphere packaging against spoilage bacteria on fresh cabbage

This study was conducted to investigate the antibacterial effects of various essential oils (EOs) against pathogens using the disc volatilization method. Also, combined effects of EOs in vapor phase and MAP were evaluated for reducing levels of total mesophilic microorganisms on fresh cabbage. The vapor phase activities of EOs (thyme-1, oregano-1, lemongrass-1, and lemongrass-2 oils) observed strong inhibitory effects. The MAP results showed that 100% CO2 gas packaging reduced significantly levels of total mesophilic microorganisms on cabbage and radish sprouts, and their reduction level was 1.55 and 2.26 log10 CFU/g compared to control after 21 days of storage (p ≤ 0.05). Based on previous results, combined effects of EOs in vapor phase and MAP (100% CO2) showed that lemongrass-2 oil with 20 discs showed complete inactivation by <1.0 log10 CFU/g after 14 days of storage. These results could provide useful information for developing alternative preservation method to improve the freshness and shelf-life of fresh produce using natural antimicrobials.

Antifungal Activity and Chemical Composition of Thyme, Peppermint and Citronella Oils in Vapor Phase against Avocado and Peach Postharvest Pathogens

AbstractThe antifungal activity of three essential oils thyme: (Thymus vulgaris L), peppermint, (Mentha piperita L) and citronella (Cymbopogen nardus); against two avocado postharvest fungal pathogens: Colletotrichum gloeosporioides (anthracnose), Lasiodiplodia theobromae (stem‐end rot); and three peach pathogens: Monilinia fructicola (brown rot), Rhizopus stolonifer (Rhizopus rot) and Penicillium expensum (blue mould rot), was assayed using a disc volatilization method. In vitro study revealed that in the vapor phase, thyme oil at 5 μL/plate as opposed to peppermint and citronella oils completely inhibited the radial mycelia growth of all five pathogens. gas chromatograph/mass spectrometry analysis showed thymol (58.77%), menthol (46.45%) and R (+) citronellal (27.59%) as the major compounds in thyme, peppermint and citronella oils, respectively. Thyme oil vapor showed a fungicidal effect on C. gloeosporioides, L. theobromae and R. stolonifer at 5 μL/plate. Thyme oil vapor at 66.7 μL/L significantly reduced anthracnose and stem‐end rot in artificially wounded and infected fruit. Therefore, these results suggest that thyme oil vapors could be used as alternate natural fungicide to control the common postharvest diseases in avocado.Practical ApplicationsGrowers and suppliers of fresh produce are faced with the challenge of providing consumers with products that are attractive, free from disease, defects and toxic residues, and with longer shelf or storage life. The strict regulations enforced by the fresh produce‐importing countries regarding the minimum pesticide residue levels in the edible portion of the fresh produce, increasing resistance to synthetic fungicides by fungal pathogens, waste disposal of fungicides and growing concerns to lower the associated environmental footprint have necessitated the search for a natural novel fungicide to replace synthetic fungicide applications in the packing line as postharvest treatment. Consumer preference to organic fresh produce is increasingly becoming popular in developed countries. On the other hand, synthetic fungicide applications are expensive for small‐scale farmers from developing countries. Therefore, considering all the reasons mentioned earlier, the results of our study provide a novel practical tool using thyme oil vapors to reduce losses because of postharvest diseases in avocado, and thus ensuring safe food.

Testing the antimicrobial activity of essential oils

The vapor phase of some essential oils proved to have antimicrobial activity. Utilization of the vapor phase of Eos is presently understood as one of the possible alternatives to synthetic food preservatives which could be used in the future. However, testing the vapor phase of EOs against microorganisms causing food-borne diseases (e.g. Salmonella enteritidis or Staphylococcus aureus) or food spoilage is relatively new. Consequently, due to the large number of known EOs, research on their antimicrobial activity is still largely in the phase of in vitro rather than in vivo testing. Moreover, no standard and reliable method for fast screening of a wide range of samples exists. Thus, the aim of this study is to show results concerning tests of the antimicrobial activity of EOs against S. enteritidis or S. aureus, which were conducted by two modifications of the disc volatilization method we developed. The lately developed method has the potential to become widely used for fast screening of EO antimicrobial activity in the vapor phase.

Fast screening method for assessment of antimicrobial activity of essential oils in vapor phase

Among promising alternative methods to control food spoilage much attention is being paid to the use of essential oils (EOs), and lately also to their activity in vapor phase. Until now, no standard assay exists, and there are many methods used by different authors, but any of them is suitably adapted for fast screening of large quantities of samples. We have modified most commonly used disc volatilization method by using four-section Petri dish (PD, 90mm diameter), large filter paper disc (85mm diameter) evenly impregnated with EO and medium containing lid. In comparison to normal disc volatilization method, labor and material needed are several times reduced, while the composition of headspace is more uniform than in case of 6mm disc, where different volatility of particular compounds could influence the results. Sixty nine EOs were tested for its antimicrobial activity against three bacteria (Staphylococcus aureus, Salmonella enteritidis, Pseudomonas aeruginosa) and three fungi (Alternaria alternata, Aspergillus niger, Penicillium digitatum). Thirty nine EOs inhibited at least one microorganism, Armoracia rusticana and Cinnamomum zeylanicum being the most active, followed by EOs of Eugenia caryophyllata, Origanum compactum, Origanum vulgare, Pimenta racemosa, Thymus serpyllum and Thymus vulgaris inhibiting all six or five microorganisms, respectively. According to our opinion, this method is suitable for screening of large quantities of samples for antimicrobial activity in vapor phase.

Antimicrobial potential and chemical composition of Mentha piperita oil in liquid and vapour phase against food spoiling microorganisms

Antimicrobial potential of Mentha piperita oil in liquid and vapour phase against different bacterial strains ( Escherichia coli αDH5, Escherichia coli ATCC 25922, Pseudomonas aeruginosa, Pseudomonas fluorescens, Bacillus subtilis and Staphylococcus aureus), fungal strains ( Penicillium digitatum, Aspergillus flavus, Aspergillus niger, Mucor spp, and Fusarium oxysporum) and yeasts ( Candida albicans and Sacchromyces cerevisiae) was determined by agar dilution method, well diffusion method and disc volatilization method, respectively. Minimum inhibitory concentration (MIC) and Minimum bactericidal and fungicidal concentration (MBC/MFC) of M. piperita oil varied from 1.13 to 2.25 mg/ml and 2.25 to 9 mg/ml for bacterial strains, 1.13 to 2.25 mg/ml and 2.25 to 4.5 mg/ml for fungal strains and 1.13 mg/ml and 2.25 mg/ml for yeasts, respectively. Bacterial inhibition zone due to M. piperita oil (40 μl/well) varied from 13 mm ( P. aeruginosa) to 22 mm ( B. subtilis). Bacterial inhibition zone due to M. piperita oil (40 μl) vapour varied from 22 mm ( P. fluorescens) to 35 mm ( B. subtilis) while almost complete growth inhibition occurred in case of fungal strains. In the kill time assays, 100% reduction in viability of C. albicans and B. subtilis was found within 8 h exposure to M. piperita oil vapour. Significant morphological alterations due to the effect of M. piperita oil and oil vapour on B. Subtilis have also been observed by scanning electron microscope. Chemical constituents of the M. piperita essential oil and oil vapour have been identified by gas chromatography (GC), gas chromatography/mass spectrometry (GC–MS) and Solid phase micro extraction-gas chromatography mass spectrometry (SPME GC–MS), respectively.

Liquid and vapour-phase antifungal activities of selected essential oils against Candida albicans: microscopic observations and chemical characterization of Cymbopogon citratus.

BackgroundUse of essential oils for controlling Candida albicans growth has gained significance due to the resistance acquired by pathogens towards a number of widely-used drugs. The aim of this study was to test the antifungal activity of selected essential oils against Candida albicans in liquid and vapour phase and to determine the chemical composition and mechanism of action of most potent essential oil.MethodsMinimum Inhibitory concentration (MIC) of different essential oils in liquid phase, assayed through agar plate dilution, broth dilution & 96-well micro plate dilution method and vapour phase activity evaluated through disc volatilization method. Reduction of C. albicans cells with vapour exposure was estimated by kill time assay. Morphological alteration in treated/untreated C. albicans cells was observed by the Scanning electron microscopy (SEM)/Atomic force microscopy (AFM) and chemical analysis of the strongest antifungal agent/essential oil has been done by GC, GC-MS.ResultsLemon grass (Cymbopogon citratus) essential oil exhibited the strongest antifungal effect followed by mentha (Mentha piperita) and eucalyptus (Eucalyptus globulus) essential oil. The MIC of lemon grass essential oil in liquid phase (288 mg/l) was significantly higher than that in the vapour phase (32.7 mg/l) and a 4 h exposure was sufficient to cause 100% loss in viability of C. albicans cells. SEM/AFM of C. albicans cells treated with lemon grass essential oil at MIC level in liquid and vapour phase showed prominent shrinkage and partial degradation, respectively, confirming higher efficacy of vapour phase. GC-MS analysis revealed that lemon grass essential oil was dominated by oxygenated monoterpenes (78.2%); α-citral or geranial (36.2%) and β-citral or neral (26.5%), monoterpene hydrocarbons (7.9%) and sesquiterpene hydrocarbons (3.8%).ConclusionLemon grass essential oil is highly effective in vapour phase against C. albicans, leading to deleterious morphological changes in cellular structures and cell surface alterations.

Activity of essential oils in vapour phase against Paenibacillus larvae

Paenibacillus larvae subspecies larvae, a Gram-positive, spore-forming bacterium, is the causative agent of the American foulbrood (AFB), one of the most serious and destructive brood diseases of honeybees. AFB is a problem for beekeepers world-wide [1]. Thus, in this study we have tested eight essential oils from aromatic plants against two strains of P. larvae, one wild strain isolated from infected honeybee colony (15/08f4) and one standard strain (ATCC 9545). For the tests we have used disc volatilization method, as the application of chemicals in vapour phase in the beehives is simple and common. In addition, several products containing thymol against parasitic mite Varroa destructor are commercially available. Four essential oils were active in the range of tested concentrations (from 1 to 256 nl/ml). The most active was EO from Armoracia rusticana (MICs 16 nl/ml) followed by Thymus vulgaris (MIC 64 nl/ml), Mentha spicata var. crispa (MICs 64 and 128 nl/l against wild and standard strain, respectively) and Satureja hortensis (MICs 128 and 256 nl/ml, respectively). The results are quite promising, the toxicity of active EO against honeybees and possible organoleptic changes of bee products will be checked in the next phase.

Antimicrobial properties of selected essential oils in vapour phase against foodborne bacteria

The aim of this study was to identify antimicrobial properties of essential oils in vapour phase. In vitro antibacterial activity against five foodborne bacteria ( Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella enteritidis, Staphylococcus aureus) was evaluated by disc volatilization method. The results were expressed as minimum inhibitory concentrations (MIC) in μl/cm 3 of air. Thirteen of the 27 essential oils were active at least against one bacterial strain in the range of tested concentrations (0.0083–0.53 μl/cm 3). The best results were shown by Armoracia rusticana (MIC 0.0083 μl/cm 3) against all of the strains, followed by Allium sativum > Origanum vulgare > Thymus vulgaris > Satureja montana, Thymus pulegioides > Thymus serpyllum > Origanum majorana > Caryopteris x clandonensis, Hyssopus officinalis, Mentha villosa, Nepeta x faassenii, Ocimum basilicum var. grant verte. In conclusion, certain essential oils are highly effective in vapour phase and could be used in control of foodborne bacterial pathogens.