Minimum inhibitory concentrations of herbal essential oils and monolaurin for gram-positive and gram-negative bacteria

New, safe antimicrobial agents are needed to prevent and overcome severe bacterial, viral, and fungal infections. Based on our previous experience and that of others, we postulated that herbal essential oils, such as those of origanum, and monolaurin offer such possibilities. We examined in vitro the cidal and/or static effects of oil of origanum, several other essential oils, and monolaurin on Staphylococcus aureus, Bacillus anthracis Sterne, Escherichia coli, Klebsiella pneumoniae, Helicobacter pylori, and Mycobacterium terrae. Origanum proved cidal to all tested organisms with the exception of B. anthracis Sterne in which it was static. Monolaurin was cidal to S. aureus and M. terrae but not to E. coli and K. pneumoniae. Unlike the other two gram-negative organisms, H. pylori were extremely sensitive to monolaurin. Similar to origanum, monolaurin was static to B. anthracis Sterne. Because of their longstanding safety record, origanum and/or monolaurin, alone or combined with antibiotics, might prove useful in the prevention and treatment of severe bacterial infections, especially those that are difficult to treat and/or are antibiotic resistant.     

Essential oils against multidrug resistant gram-negative bacteria

Multi-drug resistant uropathogens are responsible for urinary tract infections. The antibacterial activity of seven essential oils, oregano, thyme, clove, arborvitae, cassia, lemongrass, tea tree) was investigated by agar diffusion method, followed by determination of minimum inhibitory (MIC) and bactericidal (MBC) concentrations against five multidrug resistant isolates namely Pseudomonas aeruginosa, Escherichia coli, Enterobacter cloaceae, Morganella morganii, Proteus mirabilis. Oregano, thyme, cassia had antibacterial activity with inhibition zones ranging 25–39 mm; clove, arborvitae, tea tree and lemongrass 12–15 mm. The essential oils showed antibacterial activities with MICs ranged from 0.005% (w/v) to 0.5% (w/v). Thyme had the same MIC and MBC on all strains. The effects of the vapors of the essential oils were also tested by placing the oils on the underside of the Petri dish lid. Thyme, oregano and cassia essential oils strongly inhibited the growth of the clinical strains of bacteria tested in vapor phase. This study demonstrates the potential of investigated essential oils as natural alternatives for further application in hospital therapies in order to retard or inhibit the bacterial growth. For the first time antibacterial effects of essential oils (clove, arborvitae, tea tree, lemongrass, and cassia) were evaluated against Enterobacter cloaceae and Morganella morganii clinical isolates.     

Sensitivity of two greenhouse pests to vapours of essential oils

Vapours of essential oils extracted from cumin, Cuminum cyminum L., anise, Pimpinella anisum L., oregano, Origanum syriacum var bevanii (Holmes) Ietswaart and eucalyptus, Eucalyptus camaldulensis Dehn., were found to be toxic to two greenhouse pests, viz. the carmine spider mite, Tetranychus cinnabarinus (Boisd.) (Tetranychidae, Tetranychini) and cotton aphid, Aphis gossypii Glov. (Aphididae, Aphidini). In general, a minimum dose of 0.5 µl/l air and 2–3 days of exposure was required for 99% mortality using essential oils of the first three plants.     

Sensitivity of heat-stressed yeasts to essential oils of plants.

Eight strains of yeasts (Candida lipolytica, Debaryomyces hansenii, Hansenula anomala, Kloeckera apiculata, Lodderomyces elongisporus, Rhodotorula rubra, Saccharomyces cerevisiae, and Torulopsis glabrata) were examined for changes in sensitivity to eight essential oils of plants (allspice, cinnamon, clove, garlic, onion, oregano, savory, and thyme) after being sublethally heat stressed. With the exception of garlic oil for all test yeasts, onion oil for S. cerevisiae, and oregano oil for R. rubra, the essential oils at concentrations of up to 200 ppm in recovery media did not interfere with colony formation by unheated cells. However, some oils, at concentrations as low as 25 ppm in recovery media, reduced populations of sublethally heat-stressed cells compared to populations recovered in media containing no test oils. This demonstrates that the yeasts were either metabolically or structurally damaged as a result of being exposed to elevated temperatures and that essential oils prohibited repair of injury. The size (diameter) of colonies produced on oil-supplemented recovery agar by heat-stressed cells was reduced compared to that observed on unsupplemented agar. Pigment production by heated R. rubra was inhibited by oils of oregano, savory, and thyme, but enhanced by garlic and onion oils. The influence of essential oils on survival of yeasts in thermally processed foods and in the enumeration of stressed cells in these foods should not be minimized.     

Anaerobic utilization of essential oils bydenitrifying bacteria

Plant volatile organic compounds are a major carbonsource in nature. We studied the degradability ofthese substances by anaerobic microorganisms inenrichment cultures with representative essential oilsas organic substrates and nitrate as electronacceptor. Lemon and pine needle oil supportedmicrobial growth in the presence of pure oil, whereasparsley seed, camphor, sage, fennel, and mint oilsupported growth only when the essential oils weredissolved in an overlying phase of2,2,4,4,6,8,8-heptamethylnonane. Thyme oil did notsupport denitrification. Analyses of the microbiallydegraded oils revealed the disappearance ofmonoterpenes, of several monoterpenoids, and ofmethoxy-propenyl-benzenes, including apiole andmyristicin. Most-probable-number determinations fordenitrifying communities in sewage sludge and forestsoil yielded 10⁶ to 10⁷monoterpene-utilizing cells ml^-1, representing0.7 to 100% of the total cultivablenitrate-reducing microorganisms. The utilization ofessential oils together with the common occurrence ofthis metabolic trait are indications for anenvironmentally important, but currently unexploredanaerobic turnover of plant volatile organic compoundsin soil.     

Numerical taxonomy of gram-negative, nonmotile, nonfermentative bacteria isolated during chilled storage of lamb carcasses.

A numerical taxonomic study using 75 characters was performed with 132 strains of gram-negative, nonmotile, nonfermentative bacteria selected on the basis of lack of motility and Gram reaction among 1,200 cultures isolated during aerobic storage of lamb carcasses. At the 80% similarity level (SSM), eight clusters were formed. Strains in clusters 1 to 6 could be identified as members of the family Moraxellaceae and, more specifically, as members of the Psychrobacter-[Moraxella] phenylpyruvica subgroup. Of these strains, clusters 1 and 2 (88 strains) were identified as [Moraxella] phenylpyruvica and cluster 3 (15 strains) was identified as Psychrobacter immobilis. Clusters 4, 5, and 6 were not identifiable with any species. Clusters 7 and 8 consisted of 14 strains considered nonmotile variants of Pseudomonas fragi. The highest separation indices corresponded to acid production from certain carbohydrates (melibiose, L-arabinose, and cellobiose). Although strains of Psychrobacter-Moraxella clusters were relatively frequently identified at the completion of slaughter, very few cultures were detected on spoiled carcasses. It appears, therefore, that this group of organisms has only low spoilage potential.     

Numerical taxonomy of gram-negative, nonmotile, nonfermentative bacteria isolated during chilled storage of lamb carcasses.

A numerical taxonomic study using 75 characters was performed with 132 strains of gram-negative, nonmotile, nonfermentative bacteria selected on the basis of lack of motility and Gram reaction among 1,200 cultures isolated during aerobic storage of lamb carcasses. At the 80% similarity level (SSM), eight clusters were formed. Strains in clusters 1 to 6 could be identified as members of the family Moraxellaceae and, more specifically, as members of the Psychrobacter-[Moraxella] phenylpyruvica subgroup. Of these strains, clusters 1 and 2 (88 strains) were identified as [Moraxella] phenylpyruvica and cluster 3 (15 strains) was identified as Psychrobacter immobilis. Clusters 4, 5, and 6 were not identifiable with any species. Clusters 7 and 8 consisted of 14 strains considered nonmotile variants of Pseudomonas fragi. The highest separation indices corresponded to acid production from certain carbohydrates (melibiose, L-arabinose, and cellobiose). Although strains of Psychrobacter-Moraxella clusters were relatively frequently identified at the completion of slaughter, very few cultures were detected on spoiled carcasses. It appears, therefore, that this group of organisms has only low spoilage potential.     

Inhibitory activity of spices and essential oils on psychrotrophic bacteria

This study was designed to evaluate "in vitro" the inhibitory effects of spices and essential oils on the growth of psycrotrophic food-borne bacteria: Aeromonas hydrophila, Listeria monocytogenes and Yersinia enterocolitica. The sensitivity to nine spices and their oils (chilli, cinnamon, cloves, ginger, nutmeg, oregano, rosemary, sage, thyme) was studied. Antibacterial activity was evaluated on liquid and solid medium. Spices: 1% concentration of each spice was added separately to Triptic Soy Broth and then inoculated to contain 10(8)/ml organism and held to 4 degrees C for 7 days. Populations of test organism were determined on Triptic Soy Agar. Oils: Inhibition of growth was tested by using the paper disc agar diffusion method (at 35, 20 and 4 degrees C) and measuring their inhibition zone. MIC was determined by the broth microdilution method. Some culinary spices produce antibacterial activity: inhibition of growth ranged from complete (cinnamon and cloves against A. hydrophila) to no inhibition. Antibacterial inhibition zone ranged from 8 mm to 45 mm: thyme essential oil showed the greatest inhibition against A. hydrophila.     

Transformation of various species of gram-negative bacteria belonging to 11 different genera by electroporation

Summary We have undertaken a systematic study to test the transformation of various species of gram-negative bacteria using the electroporation method. The data obtained show very clearly that a great variety of gram-negative bacteria — 15 different species belonging to 11 different genera — including freshly isolated wild-type strains can be transformed efficiently by use of the electric-field mediated transformation technique. These include species of the families Enterobacteriaceae, Pseudomonadaceae, Rhizobiaceae, photosynthetic bacteria and strains for which transformation could not be achieved, up to now, by other methods.     

Metabolism of o-phthalic acid by different gram-negative and gram-positive soil bacteria

Different bacteria, isolated from soil by the enrichment method, were able to grow on phthalic acid as carbon source. Protocatechuate was identified as intermediate in phthalate metabolism. All phthalategrown bacteria oxidized phthalate and protocatechuate rapidly without having a lag-period. Benzoic acid, terephthalic acid, protocatechuic acid, salicylic acid, di- and mono-butyl phthalate were also metabolized by some of the organisms, benzoic acid being degraded via catechol and terephthalic acid via protocatechuate as intermediate. All organisms tested cleaved protocatechuate or catechol, respectively, by the ortho fission, when grown on phthalate, terephthalate, or benzoate as carbon source. A characterization and tentative identification of the organisms is given.     

Comparison of pistachio hull essential oils from different Tunisian localities

Pistachio (Pistacia vera L.) fruit is well known for its oleaginous and edible seed. Less information is available about the hull constituted by the epicarp and the mesocarp. This part of the fruit contains an essential oil that can be valorized. Tunisia is one of the countries cultivating pistachio trees. This work presents essential oil composition of pistachio hulls (Mateur variety) from different geographical localities: Grombalia (North-East), Kairouan (Middle) and Sfax (Middle-East). Yields were more important in Sfax samples (0.53% on a dry weight basis). Alpha-terpinolene was the major compound for Grombalia fruits (35.7%), whereas Kairouan and Sfax samples where characterized by alpha-pinene (42.5 and 43.8% respectively). For all samples, monoterpene hydrocarbons predominated (more than 79.8% of the essential oil).     

Anhydrobiotic engineering of gram-negative bacteria

Anhydrobiotic engineering aims to improve desiccation tolerance in living organisms by adopting the strategies of anhydrobiosis. This was achieved for Escherichia coli and Pseudomonas putida by osmotic induction of intracellular trehalose synthesis and by drying from trehalose solutions, resulting in long-term viability in the dried state.     

Bactericidal activities of essential oils of basil and sage against a range of bacteria and the effect of these essential oils on Vibrio parahaemolyticus

Basil and sage essential oils were examined for bactericidal activity against a range of Gram-positive and Gram-negative bacteria by viable count determinations. Generally, Gram-positive bacteria showed higher resistance to basil and sage essential oils than Gram-negative bacteria. Vibrio species showed a high sensitivity to both essential oils. Stationary growth phase cells of selected bacteria showed higher resistance to these essential oils than exponential growth phase cells. Basil-resistant (b21) and sage-resistant (s20) strains of Vibrio parahaemolyticus were isolated. Both strains showed higher resistance to heat and H2O2 than parent strain. Conversely, heat-adapted V. parahaemolyticus also showed a higher resistance to these essential oils than nonadapted cells.     

Rational design of a plasmid origin that replicates efficiently in both gram-positive and gram-negative bacteria

Background

Most plasmids replicate only within a particular genus or family.

Methodology/Principal Findings

Here we describe an engineered high copy number expression vector, pBAV1K-T5, that produces varying quantities of active reporter proteins in Escherichia coli, Acinetobacter baylyi ADP1, Agrobacterium tumefaciens, (all Gram-negative), Streptococcus pneumoniae, Leifsonia shinshuensis, Peanibacillus sp. S18-36 and Bacillus subtilis (Gram-positive).

Conclusions/Significance

Our results demonstrate the efficiency of pBAV1K-T5 replication in different bacterial species, thereby facilitating the study of proteins that don''t fold well in E. coli and pathogens not amenable to existing genetic tools.     

The response of gram-negative,thermophilic bacteria to oxygen

Nine gram-negative, thermophilic bacteria (LEH-1, CC-6, BI-1, NR-9, K-2,Thermus aquaticus, T. thermophilus, T. sp. X-1, andThermomicrobium roseum) tolerated increased oxygen tensions (0.6–1.0 atm). All of the strains demonstrated catalase, peroxidase, and superoxide dismutase activity. Except forT. roseum, the specific activity of one or more of these enzymes was higher under aerated culture, as compared to static conditions. Polyacrylamide gel electrophoresis (PAGE) indicated that each organism possessed only one superoxide dismutase, and each was tentatively identified as having a manganese prosthetic group. PAGE also demonstrated that the number of isozymes of catalase varied from one to three, depending on the organism. Finally, the characterization of these enzymes supported previous tentative groupings of these thermophiles.     

Inhibitory effect of oregano and thyme essential oils on moulds and foodborne bacteria

The essential oil of oregano ('origanum oil'; thymol type oil from Origanum vulgare) inhibited completely the mycelial growth of Aspergillus niger and A. flaous at 400 μg/ml, while A. ochraceus was inhibited at 600 μg/ml. At 700 μg/ml, thyme oil inhibited the mycelial growth of A. flavus and A. niger but not that of A. ochraceus . Fungal spore germination was inhibited by 600 μg/ml of origanum oil and (with the exception of A. ochraceus) by 700 μg/ml of thyme oil. Under aerobic conditions, the essential oils of oregano (250 μg/ml) and thyme (350 μg/ml) inhibited to some extent the growth of Staphylococcus aureus and Salmonella typhimurium. Pseudomonas aeruginosa was not affected by either oregano or thyme oil at concentrations up to 500 μg/ml. The origanum oil was very effective against Campylohacter jejuni and Clostridiurn sporogenes and thyme oil was very effective against C. jejuni. The antagonistic effect of the two oils on Staph. aureus and Salm. typhimuriutn was greatly enhanced when those organisms were incubated in atmospheres of low oxygen tensions