In-vitro anti-<Emphasis Type="Italic">Vibrio</Emphasis> spp. activity and chemical composition of some Tunisian aromatic plants

The chemical composition of five aromatic plants (Mentha longifolia, M. pulegium, Eugenia caryophyllata, Thymus vulgaris and Rosmarinus officinalis) frequently used in food preparation in Tunisia was analysed by GC-MS. The antimicrobial effect of the essential oils obtained from these plants was tested against Vibrio alginolyticus, Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio fluvialis strains. Thyme oil exhibited a high level of antimicrobial activities against Vibrio spp. strains. The diameter of the zones of growth inhibition for V. parahaemolyticus species was interestingly high (ranging from 14.66 to 28 mm). The MIC and MBC values were interestingly low for thyme oil (MIC 0.078–0.156 mg/ml) and (MBC >0.31–1.25 mg/ml). These results showed that these plants especially thyme and clove, can be to be used for seafood preparation to protect against contamination by Vibrio spp. strains. An erratum to this article can be found at     

Antibacterial activity of the leaf essential oil of <Emphasis Type="Italic">Blumea mollis</Emphasis> (D. Don) Merr.

The antibacterial activity of the leaf essential oil of Blumea mollis was assayed against 14 clinically isolated bacterial strains on Muller–Hinton Agar medium and Muller–Hinton Agar medium with 5% sheep blood. The essential oil had promising antibacterial activity against all the bacterial strains tested. The highest mean zone of inhibition and lowest values of minimum inhibitory concentration were recorded against methicillin-resistant Staphylococcus aureus followed by beta hemolytic Streptococcus pyogenes. The Gram-positive bacteria were more sensitive than Gram-negative bacteria. Among the bacterial strains tested, Psudomonas aeruginosa was resistant to the essential oil. The results of the present study suggest that the essential oil of B. mollis is one of the new medicinal resources as an antibacterial agent against the bacterial strains tested.     

Comparison of solid‐phase cytometry and the plate count method for the evaluation of the survival of bacteria in pharmaceutical oils

Aim: To compare the survival of four bacterial strains (Escherichia coli, Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa) in pharmaceutical oils, including jojoba oil/tea tree oil, carbol oil, jojoba oil and sesame oil. Methods and Results: Oils were spiked with the test bacteria in a concentration of 10⁴ CFU ml^?1. Bacteria were extracted from oils with phosphate‐buffered saline containing 0·5% Tween 20. Aliquots of the pooled water layers were analysed by solid‐phase cytometry and plate counting. Plate counts dropped to zero for all test strains exposed for 24 h to three of the four oils. In contrast, significant numbers of viable cells were still detected by SPC, except in the jojoba oil/tea tree oil mixture and partly in sesame oil. Conclusions: Exposure of bacteria for 24 h to the two oils containing an antimicrobial led to a loss of their culturability but not necessarily of their viability. The antibacterial activity of the jojoba oil/tea tree oil mixture supersedes that of carbol oil. Significance and Impact of the Study: These in vitro data suggest that the jojoba oil/tea tree oil mixture more than carbol oil inhibits bacterial proliferation when used for intermittent self‐catherization.     

Antimicrobial Activities of the Essential Oils of Various Plants against Tomato Late Blight Disease Agent Phytophthora infestans

The aim of this study was to find an alternative to synthetic fungicides currently used in the control of devastating oomycete pathogen Phytophthora infestans, causal agent of late blight disease of tomato. Antifungal activities of essential oils obtained from aerial parts of aromatic plants such as oregano (Origanum syriacum var. bevanii), thyme (Thymbra spicata subsp. spicata), lavender (Lavandula stoechas subsp. stoechas), rosemary (Rosmarinus officinalis), fennel (Foeniculum vulgare), and laurel (Laurus nobilis), were investigated against P. infestans. Both contact and volatile phase effects of different concentrations of the essential oils used were determined by using two in vitro methods. Chemical compositions of the essential oils were also determined by GC-MS analysis. Major compounds found in essential oils of thyme, oregano, rosemary, lavender, fennel and laurel were carvacrol (37.9%), carvacrol (79.8), borneol (20.4%), camphor (20.2%), anethole (82.8%) and 1,8-cineole (35.5%), respectively. All essential oils were found to inhibit the growth of P. infestans in a dose-dependent manner. Volatile phase effect of oregano and thyme oils at 0.3 μg/ml air was found to completely inhibit the growth of P. infestans. Complete growth inhibition of pathogen by essential oil of fennel, rosemary, lavender and laurel was, however, observed at 0.4–2.0 μg/ml air concentrations. For the determination of the contact phase effects of the tested essential oils, oregano, thyme and fennel oils at 6.4 μg/ml were found to inhibit the growth of P. infestans completely. Essential oils of rosemary, lavender and laurel were inhibitory at relatively higher concentrations (12.8, 25.6, 51.2 μg/ml respectively). Volatile phase effects of essential oils were consistently found to be more effective on fungal growth than contact phase effect. Sporangial production was also inhibited by the essential oil tested. Light and scanning electron microscopic (SEM) observation on pathogen hyphae, exposed to both volatile and contact phase of oil, revealed considerable morphological alterations in hyphae such as cytoplasmic coagulation, vacuolations, hyphal shrivelling and protoplast leakage.     

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.     

Root-promoting rhizobacteria in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> cuttings

Cloned Eucalyptus spp. plantations are based in greenhouse production of plants generated by vegetative propagation. Diverse studies have demonstrated that rhizospheric bacteria can stimulate plant growth, and more recently that they can increase rooting in vegetative material. Considering this potential, the objective of this study was to verify the effect of bacterial strains on rooting Eucalyptus globulus. A total of 132 bacterial strains isolated from the rhizosphere of E. globulus and Eucalyptus nitens were studied. The bacterial inoculums in a concentration of 4 × 10⁸ cfu/ml were applied to the rooting substrate at the cutting installation and 45 days after by irrigation. Rooting was evaluated on days 60 and 75 after cutting installation, considering the number of roots as well as their fibrosity and roots biomass. Of the 132 strains evaluated, 26 significantly increased cutting rooting in a range of 191.4–69.4% with respect to the control. Additionally, some strains stimulated the development of fine roots and incremented the roots biomass. The strains identificated that produced a rooting effect were: Bacillus firmus, Bacillus mycoides, Bacillus stearothermophilus, Bacillus subtilis, B. subtilis/amyloliquefaciens, Bacillus circulans, Brevibacillus brevis, Paenibacillus lautus and Stenotrophomona maltophilia. These first trials suggest the potential of these bacteria to be used in clonal production programs for E. globulus.     

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.     

Biosurfactant production by two isolates ofPseudomonas aeruginosa

Two strains of biosurfactant-producing bacteria, identified asPseudomonas aeruginosa, were isolated from injection water and crude oil-associated water in Venezuelan oil fields. Both biosurfactants resembled rhamnolipids and produced stable emulsions of heavy and extra-heavy crude oils, reducing the surface tension of water from 72 to 28 dynes/cm. Tenso-active properties of the biosurfactants were not affected by pH, temperature, salinity or Ca²⁺ or Mg²⁺ at concentrations in excess of those found in many oil reservoirs in Venezuela.     

Bactericidal activity of some plant essential oils against Ralstonia solanacearum infection

Potato plants and their tubers in Egypt are affected by one of the most renowned soil-borne pathogen, Ralstonia solanacearum, that caused brown rot in potato tubers and wilt in plants. There is no efficient therapeutic bactericide so; control of bacterial wilt is very rough.The study investigated three different concentrations of seven essential plant oils under in vitro and in vivo conditions as a result of their effects on Ralstonia solanacearum growth and their possibility use as potato seed pieces dressing for controlling bacterial wilt disease incidence. In vitro, anise oil at the three tested different concentrations (0.04, 0.07, and 0.14% vol/vol) was the most effective one inhibiting the growth of T4 and W9 isolates of Ralstonia solanacearum then pursued by thyme, lemongrass, and clove oils. On the other hand, rocket oil at the tested concentration was the least effective one followed by fennel oil. However, wheat germ oil was not completely effective. In vivo, experiment revealed that anise oil at the three concentrations significantly reduced disease incidence and severity in sponta and hermes potato cultivars and their effect was associated with increase of peroxidase, polyphenoloxidase, phenols and the foliar fresh weight of treated plants as well as the weight of tubers/plant followed by thyme and lemongrass oils compared to the infected untreated control.Morphological differences in bacterial cell structure have been observed using a transmission electron microscope (TEM). Anise oil at higher concentration caused of cell wall rupture and degraded cellular components.     

Phylogenetic analysis of epiphytic marine bacteria on Hole-Rotten diseased sporophytes of <Emphasis Type="Italic">Laminaria japonica</Emphasis>

During an occurrence of Hole-Rotten Disease of Laminaria japonica in a cultivating farm in Ma Shan Shandong province, China, 42 Gram-negative epiphytic marine bacteria were isolated and purified on Zobell 2216E marine agar medium. Morphological and biochemical characteristics of each isolated bacterium were studied, and molecular identification of bacterial strains was conducted with polymerase chain reaction amplification to 16S rRNA gene sequence analysis. Based on nearly full length of 16S rRNA gene sequence analysis, the isolated strains were bacteria that belong to genus Pseudoalteromonas, Vibrio, Halomonas and Bacillus. The percentage of each group was 61.9%, 28.6%, 7.1% and 2.4% respectively. The results of pathogenicity assay showed that 12 strains could cause the disease symptoms in sporophytes of L. japonica. They belonged to the genera Pseudoalteromonas, Vibrio and Halomonas with 58.3%, 33.3%, 8.3% respectively. The results suggest that these bacteria are the dominant marine bacteria on diseased sporophytes of L. japonica and may be the potential pathogenic bacteria associated with Hole-Rotten Disease of L. japonica.     

Effect of two plant extracts and Lactobacillus fermentum on colonization of gastrointestinal tract by Salmonella enterica var. Düsseldorf in chicks

According to published data, it is well known that essential oils from plants possess antimicrobial activity against a wide range of pathogens, including Salmonella strains. The influence of the administration of essential oils from oregano (Origanum vulgare) and thyme (Thymus vulgaris) as well as Lactobacillus fermentum on crop, caecum, liver and spleen colonization by Salmonella enterica var. Düsseldorf in chicks was investigated in this study. For the experiment, one hundred 1-day old chicks were used, and they were divided into four groups: (i) untreated (C); (ii) treated with L. fermentum (L); (iii) treated with a mixture of oregano and thyme essential oils (OT); and (iv) treated with a combination of L. fermentum and a mixture of oregano and thyme essential oils (LOT). Essential oils from oregano and thyme were mixed with commercial poultry diet, which was offered ad libitum to chicks in appertaining groups. L. fermentum was added daily to drinking water. After 3 days all the chicks were challenged orally with S. enterica var. Düsseldorf. The crops, ceca, spleens and livers of the birds were examined for S. enterica var. Düsseldorf colonization 5 days after the challenge. Our results showed that a combined administration of L. fermentum and essential oils (oregano and thyme) in group with combined application of essential oils and lactobacillus strain reduced the percentage of colonized crops and ceca when compared to the control group without any treatment. Presented at the Second Probiotic Conference, Košice, 15–19 September 2004, Slovakia.     

Evaluation of the anti-<Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp <Emphasis Type="Italic">cicer</Emphasis> and anti-<Emphasis Type="Italic">Alternaria porri</Emphasis> effects of some essential oils

The anti-Fusarium oxysporum f. sp cicer (FOC) and anti-Alternaria porri (A. porri) effects were evaluated for 75 different essential oils. The most active essential oils found were those of lemongrass, clove, cinnamon bark, cinnamon leaf, cassia, fennel, basil and evening primrose. However, the effectiveness of these essential oils with both the tested fungi showed different responses. The level of inhibition was compared with Hexaconazole. GC–MS analysis for five oils amongst the 75 essential oils tested was performed. The potential of these essential oils as an ecofriendly and economic approach as a fungicide for FOC and A. porri is discussed.     

Essential oils: effects of application rate and modality on potential for combating northern fowl mite infestations

The northern fowl mite (NFM), Ornithonyssus sylviarum (Mesostigmata: Macronyssidae), is the primary blood‐feeding ectoparasite found on poultry in the U.S.A. Three experiments were conducted in vitro to test the acaricidal properties of cade, garlic, lavender, lemongrass, pine and thyme essential oils against NFM, and to evaluate whether these effects are altered by adjusting oil application rates and application modality (direct vs. vapour contact). Applied at the rate of 0.21 mg/cm², the essential oils of cade, thyme, lemongrass and garlic resulted in higher NFM mortality at 24 h post‐application than lavender and pine oils, and the untreated and ethanol‐treated controls. Cade and thyme were the most consistent and fast‐acting of the essential oils in terms of toxicity to NFM. Cade applied at 0.21 mg/cm² and 0.11 mg/cm² and thyme applied at 0.21 mg/cm² were effective in eliminating NFM within 2 h through direct contact. The modality of application did not affect the efficacy of cade and thyme essential oils. The results suggest that essential oils may be utilized as alternatives to chemical pesticides and could be used as fumigants for the control of NFM.     

Effect of some essential oils on mycelial growth of <Emphasis Type="Italic">Penicillium digitatum</Emphasis> Sacc.

The antifungal action of four essential oils of Foeniculum vulgare (fennel), Thymus vulgaris (thyme), Eugenia caryophyllata (Clove) and Salvia officinalis (sage) was tested in vitro against Penicillium digitatum Sacc. Direct contact and vapour phase were used to test the antifungal activity of these essential oils against P. digitatum that is responsible for green mould rot of citrus fruits. The vapour phase and direct contact of clove and thyme essential oils exhibited the strongest toxicity and totally inhibited the mycelial growth of the test fungus. Thyme and clove essential oils completely inhibited P. digitatum growth either when added into the medium 600 μl l⁻¹ or by their volatiles with 24 μl per 8 cm diameter Petri dish. In in vitro mycelial growth assay showed fungistatic and fungicidal activity by clove and thyme essential oils. Sage and fennel oils did not show any inhibitory activity on this fungus. Scanning electron microscopy (SEM) was done to study the mode of action of clove oil in P. digitatum and it was observed that treatment with the oil leads to large alterations in hyphal morphology.     

Antimicrobial activity of essential oils of Thymus vulgaris and Origanum vulgare on phytopathogenic strains isolated from soybean

The aim of this work was to study the antimicrobial activity of essential oils obtained from Thymus vulgaris (thyme) and Origanum vulgare (oregano) on phytopathogenic Pseudomonas species isolated from soybean. Strains with characteristics of P. syringae were isolated from leaves of soybean plants with blight symptoms. Ten of these could be identified in Group Ia of LOPAT as P. syringae. Six of these were confirmed as P. syringae using 16S rRNA, indicating the presence of these phytopathogenic bacteria in east and central Argentina. All the phytopathogenic bacteria were re‐isolated and identified from the infected plants. MIC values for thyme were 11.5 and 5.7 mg·ml^?1 on P. syringae strains, while oregano showed variability in the inhibitory activity. Both essential oils inhibited all P. syringae strains, with better inhibitory activity than the antibiotic streptomycin. The oils were not bactericidal for all pseudomonads. Both oils contained high carvacrol (29.5% and 19.7%, respectively) and low thymol (1.5%). Natural products obtained from aromatic plants represent potential sources of molecules with biological activity that could be used as new alternatives for the treatment of phytopathogenic bacteria infections.     

The activity of thyme essential oil against <Emphasis Type="Italic">Acinetobacter</Emphasis> spp.

The aim of this work was to investigate the antimicrobial properties of thyme essential oil against clinical multiresistant strains of Acinetobacter spp. The antibacterial activity of oil was tested against standard and clinical bacterial strains of Acinetobacter genus. The agar diffusion method was used to check the inhibition of microbial growth at various concentrations of the oil from Thymus vulgaris. Susceptibility testing to antibiotics and chemotherapeutics was prepared using the disc-diffusion method. Identification of bacterial strains was carried out with the Vitek system and confirmed by PCR for Acinetobacter baumanii gyrB gene. The results of experiments showed that the oil from T. vulgaris exhibited an extremely strong activity against all of the clinical strains of Acinetobacter. Thyme oil demonstrated a very good efficacy against multiresistant strains of tested bacteria. Essential oils seems to be an excellent alternative for synthetic preparations and that is reason for an extensive assessment of their antimicrobial activity.      

Oil biodegradation by Bacillus strains isolated from the rock of an oil reservoir located in a deep-water production basin in Brazil

Sixteen spore forming Gram-positive bacteria were isolated from the rock of an oil reservoir located in a deep-water production basin in Brazil. These strains were identified as belonging to the genus Bacillus using classical biochemical techniques and API 50CH kits, and their identity was confirmed by sequencing of part of the 16S rRNA gene. All strains were tested for oil degradation ability in microplates using Arabian Light and Marlin oils and only seven strains showed positive results in both kinds of oils. They were also able to grow in the presence of carbazole, n-hexadecane and polyalphaolefin (PAO), but not in toluene, as the only carbon sources. The production of key enzymes involved with aromatic hydrocarbons biodegradation process by Bacillus strains (catechol 1,2-dioxygenase and catechol 2,3-dioxygenase) was verified spectrophotometrically by detection of cis,cis-muconic acid and 2-hydroxymuconic semialdehyde, and results indicated that the ortho ring cleavage pathway is preferential. Furthermore, polymerase chain reaction (PCR) products were obtained when the DNA of seven Bacillus strains were screened for the presence of catabolic genes encoding alkane monooxygenase, catechol 1,2-dioxygenase, and/or catechol 2,3-dioxygenase. This is the first study on Bacillus strains isolated from an oil reservoir in Brazil.     

印度块菌-云南松菌根际土壤细菌的种群组成和群落结构

以印度块菌-云南松菌根际土壤细菌为研究对象,研究其种群组成和结构特征。(1)稀释平板法分离得到印度块菌-云南松菌根际土壤细菌的纯培养菌株,对菌株的16S rRNA序列测序分析,对测序的菌株数量和得到的OTUs数量绘制物种累积曲线,当物种累积曲线趋于平缓时,对OTUs进行系统发育分析,揭示可培养细菌的种群组成和结构特征。(2)对印度块菌-云南松菌根际土壤细菌16S rRNA基因的V3—V4区进行高通量测序,分析全部细菌类群的种群组成和结构特征。(1)分离得到菌根际可培养细菌793株,分属于3个属的61个OTUs,其中假单胞菌属(Pseudomonas)序列占总序列的86%,不动杆菌属(Acinetobacter)序列占总序列的9.8%,链霉菌属(Streptomyces)序列占总序列的6.5%。假单胞菌是印度块菌-云南松菌根际土壤可培养细菌的绝对优势类群。(2)高通量测序得到菌根际细菌序列8937条,分属于20个门、198属、2073个OTUs。隶属于变形菌门(Proteobacteria)、放线菌门(Actinobacteria)和酸杆菌门(Acidobacteria)的OTUs占总OTUs的65.9%,变形菌门、放线菌门和酸杆菌门细菌是印度块菌-云南松菌根际土壤细菌的优势细菌。隶属于黄杆菌属(Flavobacterium)、根瘤菌属(Rhizobium)和假黄色单胞菌属(Pseudoxanthomona)的OTUs占总OTUs的33%,黄杆菌属、根瘤菌属和假黄色单胞菌属细菌是印度块菌-云南松菌根际土壤细菌的优势属。印度块菌-云南松菌根际土壤可培养细菌多样性较低,假单胞菌属细菌占据绝对优势地位。印度块菌-云南松菌根际土壤细菌类群具有较高的多样性,物种种类丰富,优势菌群集中。     

小花老鼠簕可培养细菌多样性及其生物学活性研究

小花老鼠簕(Acanthus ebracteatus)是一种生长在红树生态系统的珍稀真红树植物,具有较高的药用价值。为研究小花老鼠簕内生及根际可培养细菌多样性,挖掘其潜在新物种及具有特殊生物学活性的菌株,该文利用7种不同培养基,通过传统稀释涂布法对小花老鼠簕各植物组织及根际土壤可培养细菌进行分离,基于16S rRNA基因序列解析其内生及根际细菌群落结构和多样性特征,应用植物病原菌平板对峙实验和平铺捕食活性测试分析其可培养细菌的抗菌活性。结果表明：(1)基于16S rRNA基因序列分析,发现从小花老鼠簕的根、茎、叶、花及根际土壤中分离得到144株可培养细菌,这些细菌隶属于18目26科37属66种,芽孢杆菌属(Bacillus)和链霉菌属(Streptomyces)为优势菌属,分别占细菌种数的15.1%和13.6%;(2)拮抗多种植物病原菌试验结果显示,获得29株具有拮抗植物病原菌活性的细菌,10株具有广谱抑菌活性,其中链霉菌属菌株拮抗作用最强且菌株Y129为潜在新物种。(3)捕食活性测试结果显示,有5株细菌对金黄色葡萄球菌(Staphylococcus aureus)、耐甲氧西林金黄色葡...     

Acaricidal Activity of Pla.nt Essential Oils against Tyrophagus putrescentiae (Acari: Acaridae)

The acaricidal activity of 54 commercially available plant essential oils against Tyrophagus putrescentiae adults was compared with those of benzyl benzoate and N, N-diethyl-m-toluamide (deet). Responses varied with test oils. In a test with an impregnated fabric disc bioassay at 12.7 μg/cm², over 80% mortality was observed with bay, citronella java, clove bud, clove leaf, lemongrass, nutmeg, oregano, pimento berry, thyme red, and thyme white oils. These oils were more toxic to T. putrescentiae adults than benzyl benzoate and deet. At 6.4 μg/cm², lemongrass and thyme white oils exhibited 76 and 84% mortality, respectively, whereas the acaricidal activity of the other essential oils was significantly decreased. In a fumigation test with adult mites, lemongrass and pimento berry oils were much more effective in closed containers than in open ones, indicating that the effects of these oils were largely due to action in the vapor phase. Plant essential oils described merit further study as potential T. putrescentiae control agents.