Vapour phase: a potential future use for essential oils as antimicrobials?

Essential oil (EO) vapours have been known for their antimicrobial properties since the 4th century B.C.; however, it was not until the early 1960s that research into the potential of these volatile oils was explored. More recently, the use of EOs such as tea tree, bergamot, lavender and eucalyptus in vapour form has been shown to have antimicrobial effects against both bacteria and fungi, with range of methods being developed for dispersal and efficacy testing. To date, many applications for EO vapours as antimicrobials have been identified including in the food and clinical arenas.     

Vapour–phase activities of essential oils against antibiotic sensitive and resistant bacteria including MRSA

Aims:  To determine whether essential oil (EO) vapours could reduce surface and airborne levels of bacteria including methicillin-resistant Staphylococcus aureus (MRSA).
Methods and Results:  The antibacterial activity of geranium and lemongrass EO individually and blended were evaluated over a range of concentrations by direct contact and vapour diffusion. The EO were tested in vitro against a selection of antibiotic-sensitive and -resistant bacteria, including MRSA, vancomycin-resistant Enterococci (VRE), Acinetobacter baumanii and Clostridium difficile . An EO blend containing lemongrass and geranium was used to formulate BioScent^TM that was dispersed into the environment using the ST Pro^TM machine. The effects were variable depending on the methods used. In a sealed box environment, MRSA growth on seeded plates was reduced by 38% after 20 h exposure to BioScent^TM vapour. In an office environment, the ST Pro^TM machine dispersing BioScent^TM effected an 89% reduction of airborne bacteria in 15 h, when operated at a constant output of 100%.
Conclusions:  EO vapours inhibited growth of antibiotic-sensitive and -resistant bacteria in vitro and reduced surface and airborne levels of bacteria.
Significance and Impact of the Study:  Results suggest that EO vapours, particularly Bioscent^TM, could be used as a method of air disinfection.     

植物精油的抗菌特性及在食品工业中应用研究新进展

概述了植物精油和其单组分的来源、安全性评价、抗菌性能以及在食品工业上应用研究的新进展。并简要讨论了在食品应用中,食物中脂肪、蛋白、水、盐、pH等含量以及外在条件如包装、精油的添加形态和病菌的特性对植物精油的抗菌活性的影响。     

In vitro assessment of antimicrobial activity of carvacrol, thymol and cinnamaldehyde towards Salmonella serotype Typhimurium DT104: effects of pig diets and emulsification in hydrocolloids

AIMS: To determine the effect of pig diets in vitro on the antimicrobial activity of carvacrol, thymol and cinnamaldehyde, and to identify an emulsifier/stabilizer that can stabilize the essential oil (EO) components in aqueous solution and retain their antimicrobial activity in the presence of the diets. METHODS AND RESULTS: Emulsification of essential oil components with hydrocolloid solution was achieved by blending with a Polytron. Antimicrobial activity was measured through in vitro assays to determine the inhibition of bacterial growth by measuring the optical density at 600 nm or plating on nutrition agar after incubation of the mixtures of an EO component with the culture of Salmonella serotype Typhimurium DT104 in the presence or absence of pig diets. The results generated through the in vitro assays indicated that pig diets were able to abolish the antimicrobial activity of EOs. Xanthan, fenugreek and yellow mustard gums were the best in forming stable emulsions of five different EO components among ten different plant polysaccharides and surfactants examined. Emulsification of all the EO components in the fenugreek gum solution did not alter their antimicrobial activity. However, the antimicrobial activity of geraniol was significantly reduced when emulsified with other polysaccharides and surfactants. Both fenugreek and xanthan gum solutions were unable to protect the antimicrobial activity of carvacrol and thymol when mixed with the diets. Although cinnamaldehyde required no emulsification, but a high concentration (equivalent to at least three times of minimum bactericidal concentration for cinnamon oil) to inhibit Salmonella growth significantly in the presence of the diets, emulsification in fenugreek gum appeared to be essential for cinnamaldehyde solution to retain its antimicrobial activity during storage. CONCLUSIONS: The diets for newly weaned pigs were a significant factor limiting the antimicrobial activity of EOs and their components. Cinnamaldehyde required a high concentration to retain its antimicrobial activity in the diets, in addition to its requirement for emulsification to stabilize its activity during the storage. SIGNIFICANCE AND IMPACT OF THE STUDY: The assay with the diets used in this study for measuring the antimicrobial activity can be used in vitro for rapid and effective screening of potential antimicrobials for swine production. This study has identified polysaccharides that are able to stabilize EO component solutions. It has also identified cinnamaldehyde for further in vivo studies that may have potential in future application in controlling Salmonella and possibly other enteric pathogens in swine production.     

薄荷精油抗菌活性研究

采用气相色谱—质谱联用仪分析了薄荷精油的成分,在鉴定出的21种成分中,异佛尔酮(41.22%)、β-石竹烯(10.01%)、斯巴醇(2.89%)、β-蒎烯(1.45%)和桉树脑(1.13%)为主要成分。采用琼脂扩散法和微量肉汤稀释法对薄荷精油的抗菌活性进行了研究。结果表明,枯草芽孢杆菌及变形杆菌出现最大的抑菌环。MIC实验中,薄荷精油的浓度范围为5.00%~0.039%。在所选的8种菌种中,变形杆菌的MIC及MBC值最低,分别为0.625%及1.25%。结果充分证明,薄荷精油对于所选的8种病原菌都有很好的抗菌活性,在食品及制药工业中有广阔的应用前景。     

Ecophysiological attributes of Salmonella typhimurium in liquid culture and within a gelatin gel with or without the addition of oregano essential oil

The growth of Salmonella typhimurium in liquid culture and in a gel matrix system at two pH values (5.0 and 7.0) with (0.03% w/v) or without oregano essential oil was studied. It was shown that the type of growth media (liquid or gel) influenced significantly both the type of end-product formation and growth of bacteria as well as the inhibitory efficacy of the essential oil. The oil inhibited S. typhimurium more strongly in the liquid medium than in the gelatin matrix. In particular, the addition of essential oil in gelatin matrix delayed the initiation of growth and caused a slight suppression of the maximum population level, while in liquid culture, growth was prevented completely in identical conditions. Structure also was found to affect the rate of consumption of glucose and the rate of production of end products. Formic and acetic acids were produced in both systems, while an unidentified peak was formed only in broth samples.     

芳香植物精油的抗菌性及在动物生产中的应用

芳香植物精油为具特征性气味的挥发性油状液体, 是从芳香植物中提取的一种重要次生代谢物质。芳香植物精油的抗菌活性由其化学成分和浓度决定, 其中酚类、含氧萜类和萜烯类在抗菌方面表现出较强的活性。芳香植物精油的抗菌机制主要涉及脂肪酸外膜的改变、细胞质膜的损坏、质子动力的消耗、代谢物及离子泄露。在畜牧业生产体系中, 抗生素的无序使用不仅可能引发“超级细菌”的产生, 其残留亦会造成畜产品不安全和环境污染。芳香植物精油作为一种天然植物抗菌剂, 毒性较低且无残留, 作为饲料添加剂可用于维持动物机体的健康, 有望成为重要的抗生素替代品。该文阐述了芳香植物精油的活性成分、抗菌作用机制及其在动物生产中的应用, 为抗菌机理研究和新技术开发利用提供了理论依据。     

The effect of lemon, orange and bergamot essential oils and their components on the survival of Campylobacter jejuni, Escherichia coli O157, Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus in vitro and in food systems

AIMS: To investigate the effectiveness of oils and vapours of lemon (Citrus limon), sweet orange (Citrus sinensis) and bergamot (Citrus bergamia) and their components against a number of common foodborne pathogens. METHODS AND RESULTS: The disc diffusion method was used to screen the oils and vapours against Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Escherichia coli O157 and Campylobacter jejuni. The survival of each species, demonstrated to be susceptible in the in vitro studies, was tested on cabbage leaf for 60 s by direct contact and on chicken skin for 10 min by direct contact and 24 h by vapour. The results indicate that bergamot was the most inhibitory essential oil (EO) and citral and linalool mimicked its effect (P > 0.001). Citral and linalool vapours produced 6 log reductions in L. monocytogenes, Staph. aureus and B. cereus populations on cabbage leaf after 8-10 h exposure but bergamot vapour exposure, while producing a similar reduction in L. monocytogenes and B. cereus populations, had no effect on Staph. aureus. CONCLUSIONS: Bergamot was the most effective of the oils tested and linalool the most effective anti-bacterial component. Gram-positive bacteria were more susceptible than Gram-negative bacteria in vitro, although Camp. jejuni and E. coli O157 were inhibited by bergamot and linalool oils and by linalool vapour. All bacteria tested were less susceptible in food systems than in vitro. Of the Gram-positive bacteria tested Staph. aureus was the least susceptible to both the oils and the components tested. SIGNIFICANCE AND IMPACT OF THE STUDY: Results suggest the possibility that citrus EOs, particularly bergamot, could be used as a way of combating the growth of common causes of food poisoning.     

海南暗罗叶挥发油化学成分及其抗菌活性(英文)

本文采用水蒸气蒸馏萃取法提取海南暗罗叶挥发油化学成分,利用气相色谱-质谱(GC-MS)从中分离鉴定出40种化学成分,占挥发油总量的67.03%。其中主要成分为1-甲基-5-亚甲基-8-(1-甲基乙基)-1,6-二烯环十烷(18.305%),丁子香烯(6.256%)和γ-榄香烯(6.211%)。所得的挥发油抑菌试验表明其对大肠杆菌和枯草芽孢杆菌表现出显著的抑制活性。     

Micropropagation and acclimatization of Hedeoma multiflorum

A method for the micropropagation of Hedeoma multiflorum Benth from shoot tips or nodal segments was developed. Proliferating microshoot cultures were obtained by placing shoot tips or nodal segments on half-strength Murashige and Skoog (1962) medium supplemented with 22.2 μM BA or 22.2 μM BA plus 0.05 μM NAA. Individual shoots were excised and transferred into rooting medium containing auxins (IBA, NAA or IAA). Rooting of shoots was better on half-strength MS medium containing 0.6 μM IAA than on half-strength MS medium without growth regulators. Rooted plantlets were successfully acclimatized to soil. Preconditioning at different sucrose concentrations prior to acclimatization had no effect on plant establishment, but influenced plant quality. This revised version was published online in June 2006 with corrections to the Cover Date.     

Chemical composition and bioactivity of Boswellia serrata Roxb. essential oil in relation to geographical variation

Oleo–gum–resin of Boswellia serrata Roxb. (Burseraceae) was collected from Shivpuri forest situated in northwestern district of Madhya Pradesh, India. The commercial samples were purchased from Mandsaur and Neemuch districts (the major herbal markets of Madhya Pradesh) for comparative study of their essential oils. The average essential oil contents in the commercial Neemuch samples (11.1%) were much better as compared to the wild collection from Shivpuri (6.1%) as well as commercial collection from Mandsaur (6.9%). The commercial samples contained higher percentage of monoterpene hydrocarbons (81.9–88.1%) including α-thujene (61.4–69.8%) as the major compound. The wild habitat contained higher percentage of oxygenated monoterpenoids/benzenoids (15.7%) and sesquiterpenes (19.2%) including α-terpineol (7.8%), terpinyl isobutyrate (5.1%), and eudesmol (11.5%). Further, the antimicrobial activities of these collections showed remarkable variation among the essential oils. On the other hand, wild habitat contained improved percentage of semi-polar compounds (34.9%) which might be responsible for enhanced antibacterial activity. Similarly, the winter collection from Neemuch (BS-N2) showed significant antioxidant activity, whereas the wild habitat did not show any antioxidant activity. The higher percentage of monoterpene hydrocarbons in commercial samples, especially δ-3-carene, α-pinene, and α-thujene, might be responsible for enhanced antifungal and antioxidant activities. The Pearson correlation values justify the bioactivity relationship of the major compounds with different microbial strains. It also justified the interaction among the major individual compounds.     

Potential use of Tunisian Pituranthos chloranthus essential oils as a natural disinfectant

Aims:  To highlight the bactericidal and fungicidal activities of Tunisian Pituranthos chloranthus essential oils and to study their potential use as powerful and natural disinfectant.
Methods and Results:  The essential oils were obtained by hydro-distillation of the aerial part of P. chloranthus . The bactericidal and fungicidal properties of essential oils were investigated by using the NCCLS broth dilution method and the EN 1275 and EN 1276 European standard methods. High bactericidal and fungicidal effects of 1·87–3·75 and 7·5 mg l⁻¹ were obtained, respectively. Essential oils concentrations of 0·5% and 1% (w/v) allowed reductions in viability higher than 5 and 4 log units per ml for standard bacteria and fungi, respectively, within a contact time of 5 min under dirty conditions.
Conclusions:  Our results support the traditional uses of P. chloranthus as a natural disinfectant and insecticide. It could be used to manage life-threatening pathogens as well as food preservative.
Significance and Impact of the Study:  This natural disinfectant could play a vital role in alleviating the spread of pathogenic micro-organisms and environmental problems associated with the indiscriminate use of synthetic chemicals.     

Phytotoxic and antimicrobial activities and chemical analysis of leaf essential oil fromAgastache rugosa

Seasonal variations in the chemical composition of leaves fromAgastache rugosa were analyzed by gas chromatography-mass spectrometry (GC-MS). Phytotoxic and antimicrobial activities of its essential oil were investigated by characterizing 31 components, primarily methylchavicol (80.24%),dl-limonene (3.50%), linalool (4.23%), 5-methyl-2-(1-methylethylidene)-cyclohexanone (3.84%), and β-caryophyllene (2.39%). The contents of most of these chemical constituents varied significantly (P<0.05) over time, with the highest oil yield being early in the growing season (May). Their phytotoxic effects on the seed germination ofMajorana hortensis, Trifolium repens, Rudbeckia hirta, Chrysanthemum zawadskii var.latilobum, Melissa officinalis,Taraxacum platycarpum, andTagetes patula also were determined. These oils partially or completely inhibited germination, and prevented the growth of radicles and hypocotyls. Results of antimicrobial testing showed that the oils also entirely blocked the growth of four microorganisms (Staphylococcus aureus sub.aures, Escherichia coli, Salmonella enteritidis, andPseudomonas aeruginosa). These inhibitory effects might depend on the activity of methylchavicol, a main compound inA. rugosa.     

Screening of potential antimicrobial compounds against Xanthomonas campestris from 100 essential oils of aromatic plants used in India: an ecofriendly approach

Plants are constantly exposed to and threatened by a variety of pathogenic microorganisms present in their environments. Xanthomonas campestris is a major plant pathogen in the world. It is known to cause significant losses in many crop plants due to leaf spot and leaf blight. In the present study, bacteria isolated from infected Citrus limon fruit and identified by 16S rDNA sequencing was X. campestris. In vitro antimicrobial properties of 100 essential oils were evaluated against X. campestris. The chemical composition of the most active essential oils was investigated by gas chromatography–mass spectral (GC–MS) analysis. The potential of these essential oils as ecofriendly and economical biocontrol in agriculture is discussed.     

Susceptibility and intrinsic tolerance of Pseudomonas aeruginosa to selected plant volatile compounds

AIMS: To examine the causes for variations in sensitivity and intrinsic tolerance of Pseudomonas aeruginosa to plant volatile compounds. METHODS AND RESULTS: Minimum inhibitory concentrations were determined for a selection of volatile phytochemicals against P. aeruginosa using a microdilution assay. Effects on growth were also assessed in 100-ml broth cultures. The two strains of P. aeruginosa included in the study exhibited intrinsic tolerance to all compounds, with the exception of carvacrol and trans-cinnamaldehyde. The protonophore carbonyl cyanide m-chlorophenylhydrazone increased P. aeruginosa sensitivity to all compounds except trans-cinnamaldehyde, implicating an ATP-dependent efflux mechanism in the observed tolerance. Outer membrane integrity following treatment with test compounds was assessed by measuring sensitization to detergents. Only carvacrol caused damage to the outer membrane of P. aeruginosa. CONCLUSIONS: The intrinsic tolerance of P. aeruginosa strains to plant volatile compounds is associated with an active efflux mechanism and the barrier function of the outer membrane. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings offer an explanation for the intrinsic tolerance to plant volatile compounds exhibited by P. aeruginosa. The study also confirms that the outer membrane-permeabilizing action of carvacrol, previously reported for the gram-negative bacteria Escherichia coli and Salmonella, extends to monoterpene-tolerant strains of P. aeruginosa.