Comparison of Antimicrobial Activity of Essential Oils,Plant Extracts and Methylparaben in Cosmetic Emulsions: 2 Months Study

The aim of the study was to compare the preservative effectiveness of plant extracts (Matricaria chamomilla, Aloe vera, Calendula officinalis) and essential oils (Lavandulla officinalis, Melaleuca alternifolia, Cinnamomum zeylanicum) with methylparaben in cosmetic emulsions against skin microflora during 2 months of application by volunteers. Cosmetic emulsions with extracts (2.5 %), essential oils (2.5 %), methylparaben (0.4 %) or placebo were tested by 40 volunteers during 2 months of treatment. In order to determine microbial purity of the emulsions, the samples were taken after 0, 2, 4, 6 and 8 weeks of application. Throughout the trial period it was revealed that only cinnamon oil completely inhibited the growth of bacteria, yeast and mould, as compared to all other essential oils, plant extracts and methylparaben in the tested emulsions. This result shows that cinnamon oil could successfully replace the use of methylparaben in cosmetics, at the same time ensuring microbiological purity of a cosmetic product under its in-use and storage conditions.     

Low-Molecular-Weight Metabolites Secreted by Paenibacillus larvae as Potential Virulence Factors of American Foulbrood

The spore-forming bacterium Paenibacillus larvae causes a severe and highly infective bee disease, American foulbrood (AFB). Despite the large economic losses induced by AFB, the virulence factors produced by P. larvae are as yet unknown. To identify such virulence factors, we experimentally infected young, susceptible larvae of the honeybee, Apis mellifera carnica, with different P. larvae isolates. Honeybee larvae were reared in vitro in 24-well plates in the laboratory after isolation from the brood comb. We identified genotype-specific differences in the etiopathology of AFB between the tested isolates of P. larvae, which were revealed by differences in the median lethal times. Furthermore, we confirmed that extracts of P. larvae cultures contain low-molecular-weight compounds, which are toxic to honeybee larvae. Our data indicate that P. larvae secretes metabolites into the medium with a potent honeybee toxic activity pointing to a novel pathogenic factor(s) of P. larvae. Genome mining of P. larvae subsp. larvae BRL-230010 led to the identification of several biosynthesis gene clusters putatively involved in natural product biosynthesis, highlighting the potential of P. larvae to produce such compounds.     

Chemical composition and antimicrobial activity of Citrus essences on honeybee bacterial pathogen <Emphasis Type="Italic">Paenibacillus larvae</Emphasis>, the causal agent of American foulbrood

Antimicrobial properties and chemical composition of four citrus fruit essential oils to control Paenibacillus larvae, the causal agent of American foulbrood disease (AFB) were determined. This honeybee larvae disease occurs throughout the world and is found in many beekeeping areas of Argentina. Citrus fruit essential oils tested were those from grapefruit (Citrus paradisi), sweet orange (Citrus sinensis), mandarin (Citrus nobilis) and lemon (Citrus limon). The components of the essential oils were identified by SPME-GC/MS analysis. The antimicrobial activity of the oils against P. larvae were determined by the broth microdilution method. Two way ANOVA tests for minimum inhibitory concentrations (MICs) data and minimal bactericide concentrations (MBCs) data, indicated significant differences between the strains and the oils tested. The antimicrobial assays showed that the oil of C. paradisi inhibited the bacterial strains at the lowest concentrations tested, MICs and MBCs averages of 385.0 mg/l and 770.0 mg/l, respectively. This property could be attributed to the kind and percentage of the volatile components of the oil, like limonene (69.9%) and myrcene (9.6%). The use of essential oils or their specific volatile components individually against pests related to food provision may represent an alternative scope for the control of this serious disease because it does not leave toxic chemical residues in honey nor in its by products.     

Synergistic effect of surfactin from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> C4 and <Emphasis Type="Italic">Achyrocline satureioides</Emphasis> extracts on the viability of <Emphasis Type="Italic">Paenibacillus larvae</Emphasis>

The aim of this work was to determine the in vitro effect of the mixture between the lipopeptide surfactin, synthesized by Bacillus subtilis C4 (strain isolated from honey) and the most active vegetal extract from Achyrocline satureioides, a traditional medicinal plant, on local strains of Paenibacillus larvae, the agent of American Foulbrood in honeybees. Five P. larvae strains isolated in Córdoba, Argentina, were phenotypically characterized. These and 12 other P. larvae strains from different regions of Argentina were analysed. The antimicrobial activities of the essential oil, hexane (HE) and benzene extracts from A. satureioides were assessed against P. larvae and the HE showed the highest anti-P. larvae activity. A combination of the biosurfactant surfactin, produced by B. subtilis C4, and the HE of A. satureioides revealed a synergistic action on P. larvae. The effective surfactin concentration in the mixture decreased from 32 to 1 μg ml⁻¹ and the HE concentration from 32 to 4 μg ml⁻¹, values similar or equal to minimal inhibitory concentrations observed for oxytetracycline. The fractional inhibitory concentration index confirmed synergism in 4 strains and partial synergism in one strain. The combination of surfactin synthesized by B. subtilis C4 and the HE from A. satureioides could be a natural alternative to help beekeepers to combat the American foulbrood agent P. larvae.     

Astaxanthin Synthesis by Yeast Xanthophyllomyces dendrorhous and its Mutants on Media Based on Plant Extracts

The study evaluated the effect of media based on plant extracts: potato, carrot and barley malt broth, on growth and astaxanthin synthesis by yeast Xanthophyllomyces dendrorhous DSM 5626 and its mutants. The carrot medium promoted carotenogenesis most effectively. In cultures on this medium the highest volumetric and cellular concentrations of astaxanthin were recorded for four out of five tested strains. Also the share of astaxanthin in the total carotenoids produced by the tested strains was the highest.     

Differentiation of Paenibacillus larvae subsp. larvae, the Cause of American Foulbrood of Honeybees, by Using PCR and Restriction Fragment Analysis of Genes Encoding 16S rRNA

A rapid procedure for the identification of Paenibacillus larvae subsp. larvae, the causal agent of American foulbrood (AFB) disease of honeybees (Apis mellifera L.), based on PCR and restriction fragment analysis of the 16S rRNA genes (rDNA) is described. Eighty-six bacterial strains belonging to 39 species of the genera Paenibacillus, Bacillus, Brevibacillus, and Virgibacillus were characterized. Amplified rDNA was digested with seven restriction endonucleases. The combined data from restriction analysis enabled us to distinguish 35 profiles. Cluster analysis revealed that P. larvae subsp. larvae and Paenibacillus larvae subsp. pulvifaciens formed a group with about 90% similarity; however, the P. larvae subsp. larvae restriction fragment length polymorphism pattern produced by endonuclease HaeIII was found to be unique and distinguishable among other closely related bacteria. This pattern was associated with DNA extracted directly from honeybee brood samples showing positive AFB clinical signs that yielded the restriction profile characteristic of P. larvae subsp. larvae, while no amplification product was obtained from healthy larvae. The method described here is particularly useful because of the short time required to carry it out and because it allows the differentiation of P. larvae subsp. larvae-infected larvae from all other species found in apiarian sources.     

Biological effects of some natural and chemical compounds on the potato tuber moth,Phthorimaea operculella Zell. (Lepidoptera:Gelechiidae)

The olfactory reaction of larvae and moths was investigated towards 18 oils (6 natural oils and 12 commercial chemical oils). Some of these oils such as peppermint and camphor (natural oils) and eugenol and camphene (commercial oils) were repellent to both larvae and moths. Other oils such as strawberry and d-limonene were attractive to both larvae and moths.Some of the repellent oils were, therefore, tested for their effect on certain biological aspects of the insects.Eugenol and peppermint oils, each at the 0.01% conc., caused a significant depression in the fecundity of moth and decreased the percentage of egg hatchability. Eugenol oil was much more effective than peppermint oil at 1%. Dried (leaves, fruits or seeds) powder of 14 different plants species were tested in different concentrations with talcum powder (carrier material) against egg deposition. The results indicated that dried powders of Allium cepa, Curcuma longa, Colocasia antiqurum, Ocimum basilicum. Dodonaea viscose and Thuja orientalis played a highly significant role in reducing egg deposition. The most impressive effect was displayed by powders of D. viscose and A. cepa, which caused the highest depression in egg deposition as well as in the emerging offsprings. Ethanolic extracts of 11 plants indicated that extracts of Pithuranthos tortosus and Iphiona scabra caused the maximum inhibition of egg hatchability, followed by C. longa, Citrullus colocynthia and T. orientalis. Ethanolic extracts of Schinus terebenthiflius (leaves) and I. scabra caused the highest depression in the deposited eggs, as they played a remarkable role as ovipositor deterrents.The majority of the plant extracts at 1% conc. could protect potato tubers at different intervals according to the calculated tuber damage index as follows: Iphiopna > Pithuranthos > Curcuma > Schinus (fruits) Thuja > Schinus (leaves) > Dodonaea > Citrullus.     

Activity of some Nile River aquatic macrophyte extracts against the cyanobacterium Microcystis aeruginosa

The anti-algal activity of five macrophyte extracts on the cyanobacterium Microcystis aeruginosa in Egypt was investigated in 2013. Extract activity varied according to plant type, extracting solvent and its concentration. The highest inhibitory activity was achieved with ethanol extract at a concentration of 80 mg l^?1, followed by chloroformic extracts, at 60 mg l^?1. Methanolic extracts of Eichhornia crassipes and Polygonum tomentosum inhibited growth of Microcystis aeruginosa at all concentrations. Acetonic extracts inhibited algal growth at 60 mg l^?1, except for the extract of Ceratophyllum subdemersum, which showed stimulation of M. aeruginosa growth. Eichhornia crassipes ethanolic extract exerted the most powerful inhibition by more than five-fold, 570.17%, followed by those of P. tomentosum, Saccharum spontaneum, Ceratophyllum demersum and C. subdemersum, 559.48, 553.99, 544.11 and 366.51%, respectively. Phytochemical screening for the tested plant extracts revealed the presence of biologically active substances of different concentrations, with P. tomentosum having the highest polyphenols, 1.95% of dry weight.     

A PCR Detection Method for Rapid Identification of Paenibacillus larvae

American foulbrood is a disease of larval honeybees (Apis mellifera) caused by the bacterium Paenibacillus larvae. Over the years attempts have been made to develop a selective medium for the detection of P. larvae spores from honey samples. The most successful of these is a semiselective medium containing nalidixic acid and pipermedic acid. Although this medium allows the growth of P. larvae and prevents the growth of most other bacterial species, the false-positive colonies that grow on it prevent the rapid confirmation of the presence of P. larvae. Here we describe a PCR detection method which can be used on the colonies that grow on this semiselective medium and thereby allows the rapid confirmation of the presence of P. larvae. The PCR primers were designed on the basis of the 16S rRNA gene of P. larvae and selectively amplify a 973-bp amplicon. The PCR amplicon was confirmed as originating from P. larvae by sequencing in both directions. Detection was specific for P. larvae, and the primers did not hybridize with DNA from closely related bacterial species.     

Development and Evaluation of PCR Assays for the Detection of Paenibacillus larvae in Honey Samples: Comparison with Isolation and Biochemical Characterization

PCR assays were developed for the direct detection of Paenibacillus larvae in honey samples and compared with isolation and biochemical characterization procedures. Different primer pairs, designed from the 16S rRNA and the metalloproteinase precursor gene regions, and different DNA extraction methods were tested and compared. The sensitivity of the reactions was evaluated by serial dilutions of DNA extracts obtained from P. larvae cultures. The specificity of the primers was assessed by analyzing related Paenibacillus and Bacillus strains isolated from honey. The PCR assays also amplified these related bacteria, but at lower sensitivity. In the next step, the PCR assays were applied to contaminated honey and other bee products originating from 15 countries. Lysozyme treatment followed by proteinase K digestion was determined to be the best DNA extraction method for P. larvae spores. The most sensitive primer pair detected P. larvae in 18 of 23 contaminated honey samples, as well as in pollen, wax, and brood. Honey specimens containing saprophyte bacilli and paenibacilli, but not P. larvae, were PCR negative. Although the isolation and biochemical identification method (BioLog) showed higher sensitivity and specificity, PCR proved to be a valuable technique for large-scale screening of honey samples for American foulbrood, especially considering its rapidity and moderate costs.     

Antimicrobial activity and phytochemical analyses of Polygonum aviculare L. (Polygonaceae), naturally growing in Egypt

Polygonum aviculare (Polygonaceae) is an herb commonly distributed in Mediterranean coastal regions in Egypt and used in folkloric medicine. Organic and aqueous solvent extracts and fractions of P. aviculare were investigated for antimicrobial activities on several microorganisms including bacteria and fungi. Phytochemical constituents of air-dried powered plant parts were extracted using aqueous and organic solvents (acetone, ethanol, chloroform and water). Antimicrobial activity of the concentrated extracts was evaluated by determination of the diameter of inhibition zone against both Gram-negative and Gram-positive bacteria and fungi using paper disc diffusion method.Results of the phytochemical studies revealed the presence of tannins, saponins, flavonoids, alkaloids and sesquiterpenes and the extracts were active against both Gram-negative and Gram-positive bacteria. Chloroform extract gave very good and excellent antimicrobial activity against all tested bacteria and good activity against all tested fungi except Candida albicans. Structural spectroscopic analysis that was carried out on the active substances in the chloroform extract led to the identification of panicudine (6-hydroxy-11-deoxy-13 dehydrohetisane).Evaluation of the antimicrobial activity of panicudine indicated significant activity against all tested Gram-negative and Gram-positive organisms. Panicudine displayed considerable activity against the tested fungi with the exception of C. albicans. Antimicrobial activity of the extracts was unaffected after exposure to different heat treatments, but was reduced at alkaline pH. Studies of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of panicudine on the tested organisms showed that the lowest MIC and the MBC were demonstrated against Salmonella paratyphi, Bacillus subtilis and Salmonella typhi and the highest MIC and MBC were against Staphylococcus aureus.     

In vitro efficacies of oils, silicas and plant preparations against the poultry red mite Dermanyssus gallinae

The aim of this study was to test the effectiveness of physically acting substances (oils and silicas) and plant preparations for the control of the poultry red mite Dermanyssus gallinae (De Geer 1778). Reproduction and survival of fed D. gallinae females were evaluated in vitro for a total of 168 h using the “area under the survival curve” (AUC) to compare survival of the mites between treatments. Four oils (two plant oils, one petroleum spray oil and diesel), one soap, three silicas (one synthetic amorphous silica, one diatomaceous earth (DE) and one DE with 2% pyrethrum extract) and seven plant preparations (derived from Chrysanthemum cineariaefolium, Allium sativum, Tanacetum vulgare, Yucca schidigera, Quillaja saponaria, Dryopteris filix-mas, and Thuja occidentalis) were tested at various concentrations. All the oils, diesel and soap significantly reduced D. gallinae survival. All silicas tested inhibited reproduction. DE significantly reduced mite survival, but amorphous silica was less effective in vitro. Except for pure A. sativum juice and the highest concentration of C. cineariaefolium extract, the plant preparations tested resulted in statistically insignificant control of D. gallinae.     

Effect of Single and Interplantings on Pathogenicity of Pratyenchus penetrans and P. neglectus to Alfalfa and Crested Wheatgrass

Alfalfa is a host of Pratylenchus penetrans and P. neglectus, whereas crested wheatgrass is a host of P. neglectus but not of P. penetrans. In a 120-day greenhouse experiment at 24 ñ 3 C, P. neglectus inhibited the growth of ''Lahontan'' alfalfa and ''Fairway'' crested wheatgrass. There were no differences in persistence and plant growth of alfalfa and crested wheatgrass, or reproduction of P. neglectus, in single plantings of alfalfa (AO) or crested wheatgrass (CWO), or in interplanted alfalfa and crested wheatgrass (ACW) treatments. On alfalfa, P. penetrans inhibited growth and reproduced more than did P. neglectus. Inhibition of plant growth and reproduction of P. penetrans was greater on alfalfa in AO than in ACW treatments. Pratylenchus penetrans did not reproduce on crested wheatgrass, but inhibited growth of crested wheatgrass in interplanted treatments and was avirulent in single planted treatments. Results were similar in a controlled growth chamber experiment at 15, 20, 25, and 30 C. Both nematode species inhibited alfalfa growth at all temperatures, and P. penetrans was more virulent than was P. neglectus to alfalfa at all temperatures and treatments. Plant growth inhibition and reproduction of P. penetrans on alfalfa in single and interplanted treatments were similar at 15-20 C, but were greater in single than in interplanted treatments at 25-30 C. Pratylenchus penetrans was avirulent to crested wheatgrass in the single planted treatments at all temperatures, but inhibited growth of crested wheatgrass in interplanted treatments at 20-30 C. Plant growth and reproduction of P. neglectus on crested wheatgrass was similar in single and interplanted treatments at 20-30 C and 15-30 C, respectively.     

In vitro evaluation of antibacterial,anticollagenase, and antioxidant activities of hop components (Humulus lupulus) addressing acne vulgaris

Seven naturally derived components from hop plant (Humulus lupulus L.) extracts were tested for evaluation of biological activities affecting acne vulgaris. Five strains, Propionibacterium acnes, Staphylococcus epidermidis, Staphylococcus aureus, Kocuria rhizophila and, Staphylococcus pyogenes, were selected as the main acne-causing bacteria. Hop extracts xanthohumol and the lupulones showed strong inhibitory activities against all of the strains. Although hydrogenated derivatives did not show the same level of activity, naturally occurring xanthohumol, humulones, and lupulones all showed moderate to strong anticollagenase inhibitory activities. Antioxidant capacity was also evaluated with seven different methods based on different reactive oxygen species. Xanthohumol showed the highest activity in total oxygen radical absorbance capacity as well as singlet oxygen absorbance capacity.     

Essential Oils,Silver Nanoparticles and Propolis as Alternative Agents Against Fluconazole Resistant Candida albicans,Candida glabrata and Candida krusei Clinical Isolates

Development of effective and safe therapeutic treatment of fungal infections remains one of the major challenge for modern medicine. The aim of presented investigation was to analyze the in vitro antifungal activity of selected essential oils, ethanolic extracts of propolis and silver nanoparticles dropped on TiO₂ against azole-resistant C. albicans (n = 20), C. glabrata (n = 14) and C. krusei (n = 10) clinical isolates. Among tested essential oils, the highest activity has definitely been found in the case of the oil isolated from the bark of Cinnamomum cassia, with MIC and MFC values for all tested strains in the range of 0.0006–0.0097 % (v/v) and 0.0012–0.019 % (v/v), respectively. High activity was also observed for the Lemon, Basil, Thyme, Geranium and Clove (from buds) essential oils. Significant differences in fungicidal activity have been observed in the case of four tested propolis samples. Only one of them revealed high activity, with MFC values in the range from 0.156 to 1.25 % (v/v). Satisfactory fungicidal activity, against C. albicans and C. glabrata isolates, was also observed in the case of silver nanoparticles, however C. krusei isolates were mostly resistant. We also revealed that constituents of most of essential oils and propolis as well as silver nanoparticles are not substrates for drug transporters, which belong to the most important factors affecting resistance of Candida spp. clinical isolates to many of conventional antimycotics. To conclude, the results of our investigation revealed that essential oils, propolis and silver nanoparticles represent high potential for controlling and prevention candidiasis.     

Chemical compositions,antimicrobial and herbicidal effects of essential oils isolated from Turkish Tanacetum aucheranum and Tanacetum chiliophyllum var. chiliophyllum

The chemical composition of essential oils isolated from the aerial parts by hydrodistillation of Turkish Tanacetum aucheranum and Tanacetum chiliophyllum var. chiliophyllum were analyzed by GC–MS. The oils contain similar major components. The major components of T. aucheranum oil were 1,8-cineole (23.8%), camphor (11.6%), terpinen-4-ol (7.2%), α-terpineol (6.5%), borneol (3.8%), (E)-thujone (3.2%), epi-α-cadinol (3.1%), and artemisia ketone (3.0%). Camphor (17.9%), 1,8-cineole (16.6%) and borneol (15.4%) were found to be predominant constituents in the oil of T. chiliophyllum. It is interesting to find that ester derivatives of dihydro-α-cyclogeranic acid (2,2,6-trimethylcyclohexylcarboxylate), dihydro-α-cyclogeranyl hexanoate (10.1%), dihydro-α-cyclogeranyl pentanoate (3.0%), dihydro-α-cyclogeranyl butanoate (2.1%) and dihydro-α-cyclogeranyl propionate (1.2%) are firstly found as chemotaxonomically important components in T. chiliophyllum oil. From these, dihydro-α-cyclogeranyl hexanoate was isolated on silica gel column chromatography and its structure was confirmed by spectroscopic methods. This is the first report on the occurrence of ester derivatives of dihydro-α-cyclogeranic acid in essential oils of Tanacetum species. The oils were also characterized to have relatively high amounts of oxygenated monoterpenes. Results of the antifungal testing by microbial growth inhibition assays showed that the oils completely inhibit the growth of 30 phytopathogenic fungi. However, their growth inhibition effects were lower than commercial benomyl. The oils tested for antibacterial activity against 33 bacterial strains showed a considerable antibacterial activity over a wide spectrum. Herbicidal effects of the oils on seed germination of Amaranthus retroflexus, Chenopodium album and Rumex crispus were also determined and the oils completely inhibited the seed germination and seedling growth of the plants.     

Enhancing a search for traditional medicinal plants with anthelmintic action by using wild type and stress reporter Caenorhabditis elegans strains as screening tools

Traditional healers in Sarawak, Malaysia, use plants such as Picria fel-terrae, Linariantha bicolor and Lansium domesticum to treat gastrointestinal infections. This study aimed to test whether their nematocidal activities could be confirmed in vitro using highly standardised Caenorhabditis elegans models. We applied eight different ethanol solubilised plant extracts and two commercial anthelmintic drugs to larval and adult stages of C. elegans in vitro. Seven C. elegans strains were evaluated, one wild type and six strains with GFP-tagged stress response pathways to help characterise and compare the pathways affected by plant extracts. Our in vitro screen confirmed that both of the commercial anthelmintic drugs and five of the eight traditionally used plant extracts had significant nematocidal activity against both larval and adult C. elegans. The most effective extracts were from P. fel-terrae. The plant extracts triggered different stress response pathways from the commercial anthelmintic drugs. This study showed that using traditional knowledge of plant medicinal properties in combination with a C. elegans in vitro screen provided a rapid and economical test with a high hit rate compared with the random screening of plants for nematocidal activities. The use of transgenic C. elegans strains may allow this approach to be refined further to investigate the mode of action of active extracts.     

Plant growth promoting rhizobacteria improve growth and essential oil yield in Origanum majorana L.

Effects of root colonization by plant growth promoting rhizobacteria (PGPR) on biomass, and qualitative and quantitative composition of essential oils, were determined in the aromatic crop Origanum majorana L. (sweet marjoram). PGPR strains evaluated were Pseudomonas fluorescens, Bacillus subtilis, Sinorhizobium meliloti, and Bradyrhizobium sp. Only P. fluorescens and Bradyrhizobium sp. showed significant increases in shoot length, shoot weight, number of leaf, number of node, and root dry weight, in comparison to control plants or plants treated with other PGPR. Essential oil yield was also significantly increased relative to non-inoculated plants, without alteration of oil composition. P. fluorescens has clear commercial potential for economic cultivation of O. majorana.     

In vitro Growth Inhibition by Hypericum Extracts and Isolated Pure Compounds of Paenibacillus larvae,a Lethal Disease Affecting Honeybees Worldwide

The in vitro inhibitory potential of 50 extracts from various species of the flowering plant genus Hypericum was investigated using the Kirby? Bauer disk diffusion susceptibility test against Paenibacillus larvae, a spore‐forming, Gram‐positive bacterial pathogen that causes American foulbrood (AFB), a lethal disease affecting honeybee brood worldwide. Of the tested extracts, 14 were identified as highly active against P. larvae as compared to the activity of the positive control, indicating the presence of highly potent antibacterial compounds in the extracts. Examination of these extracts using TLC and HPLC/MS analyses revealed the presence of acylphloroglucinol and filicinic‐acid derivatives. Six pure compounds isolated from these extracts, viz., hyperforin ( 1 ), uliginosin B ( 2 ), uliginosin A ( 3 ), 7‐epiclusianone ( 4 ), albaspidin AA ( 5 ), and drummondin E ( 6 ), displayed strong antibacterial activity against the vegetative form of P. larvae (MIC ranging from 0.168–220 μM ). Incubation of P. larvae spores with the lipophilic extract of Hypericum perforatum and its main acylphloroglucinol constituent 1 led to the observation of significantly fewer colony forming units as compared to the negative control, indicating that the acylphloroglucinol scaffold represents an interesting lead structure for the development of new AFB control agents.     

Disruption of N-Αcyl Homoserine Lactone-Mediated Cell Signaling and Iron Acquisition in Epiphytic Bacteria by Leaf Surface Compounds

Since N-acyl homoserine lactones (AHLs) are key mediators of cell density-dependent regulation of traits involved in virulence and epiphytic fitness in gram-negative bacteria such as Pseudomonas syringae, a variety of plant species were examined to determine their production of leaf surface compounds that could interact with these signaling systems. Leaf washings of 17 of 52 plant species tested stimulated or inhibited AHL-dependent traits in at least one of the bacterial reporter strains used. The active compounds from most plants could be distinguished from known AHLs due to different patterns of mobility during C₈ and C₁₈ reverse-phase thin-layer chromatography (TLC) and normal-phase TLC compared to the patterns for authentic bacterial AHLs. All plant extracts were also tested to determine their abilities to sequester iron and trigger bacterial siderophore synthesis on a medium containing abundant iron. Leaf washings from 16 of the 52 plant species, as well as tannic acid solutions, stimulated pyoverdine synthesis in P. syringae in a high-iron medium. These preparations also inhibited the growth of a P. syringae mutant unable to produce pyoverdine siderophores but not the growth of the wild-type bacterium. The stimulation of siderophore production and the growth inhibition by plant extracts and purified tannins were both reversed by addition of ferric chloride to culture media, indicating that iron was made unavailable by the compounds released onto the leaf surface.