Showing papers in "Letters in Applied Microbiology in 2009"

Fabrication of silver nanoparticles by Phoma glomerata and its combined effect against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus

Abstract: Aims: We report extracellular synthesis of silver nanoparticles (Ag-NPs) from Phoma glomerata and its efficacy against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The bacteria exhibiting resistance to various antibiotics showed remarkable sensitivity, when used in combination of antibiotics and Ag-NPs. Methods and Results: Biosynthesis of Ag-NPs was carried out by challenging the fungal cell filtrate with 1 mmol l−1 silver nitrate. The Ag-NPs were characterized with the help of UV–Visible spectrophotometer and Fourier transform infrared spectroscopy. Scanning electron microscopy was carried out to detect the size of Ag-NPs. Evaluation of the combined effect(s) was studied by disc diffusion method against E. coli, Staph. aureus and Ps. aeruginosa. Conclusions: The biosynthesis route seems to be eco-friendly and easy to scale up the process. Thus, these Ag-NPs may prove as a better candidate for drugs and can potentially eliminate the problem of chemical agents because of their biogenic nature. Significance and Impact of the Study: The bacterial resistance against antibiotics has been increasing with alarming rate. To overcome this problem, there is a pressing need to develop bactericidal agents. Ag-NPs may prove to be an answer to drug-resistant bacteria.

Bifidobacterium and Lactobacillus DNA in the human placenta.

Abstract: Aims: Bifidobacteria and lactobacilli are part of the human normal intestinal microbiota and may possibly be transferred to the placenta. It was hypothesized that intestinal bacteria or their components are present in the placenta and that the foetus may be exposed to them. We investigated the presence of bifidobacteria and lactobacilli and their DNA in the human placenta. Methods and Results: We studied 34 human placentae (25 vaginal and nine caesarean deliveries) for the presence Bifidobacterium spp. and Lactobacillus rhamnosus. Cultivation was used for the detection of viable cells and genus and species-specific PCR for the detection of DNA. No bifidobacteria or lactobacilli were found by cultivation. Bifidobacterial DNA was detected in 33 and L. rhamnosus DNA in 31 placenta samples. Conclusions: DNA from intestinal bacteria was found in most placenta samples. The results suggest that horizontal transfer of bacterial DNA from mother to foetus may occur via placenta. Significance and Impact of the Study: Bacterial DNA contains unmethylated CpG oligodeoxynucleotide motifs which induce immune effects. Specific CpG motifs activate Toll-like receptor 9 and subsequently trigger Th-1-type immune responses. Although the newborn infant is considered immunologically immature, exposure by bacterial DNA may programme the infant’s immune development during foetal life earlier than previously considered.

Inhibition of quorum sensing regulated bacterial functions by plant essential oils with special reference to clove oil

Abstract: Aims: To evaluate quorum sensing (QS) inhibitory activity of plant essential oils using strains of Chromobacterium violaceum (CV12472 and CVO26) and Pseudomonas aeruginosa (PAO1). Methods and Results: Inhibition of QS-controlled violacein production in C. violaceum was assayed using disc diffusion and agar well diffusion method. Of the 21 essential oils, four oils showed varying levels of anti-QS activity. Syzygium aromaticum (Clove) oil showed promising anti-QS activity on both wild and mutant strains with zones of pigment inhibition 19 and 17 mm, respectively, followed by activity in cinnamon, lavender and peppermint oils. The effect of clove oil on the extent of violacein production was estimated photometrically and found to be concentration dependent. At sub-MICs of clove oil, 78·4% reduction in violacein production over control and up to 78% reduction in swarming motility in PAO1 over control were recorded. Gas chromatography–mass spectrometry analysis of clove oil indicated presence of many phytocompounds. Eugenol, the major constituent of clove oil could not exhibit anti-QS activity. Conclusions: Presence of anti-QS activity in clove oil and other essential oils has indicated new anti-infective activity. The identification of anti-QS phytoconstituents is needed to assess the mechanism of action against both C. violaceum and Ps. aeruginosa. Significance and Impact of the study: Essential oils having new antipathogenic drugs principle because of its anti-QS activity might be important in reducing virulence and pathogenicity of drug-resistant bacteria in vivo.

The benefits of silver in hygiene, personal care and healthcare.

Abstract: Silver has been used for centuries as an antimicrobial agent to reduce bioburden and prevent infection Its usage diminished when antibiotics were introduced but remained one of the most popular agents for wound infections, especially in burned patients Incorporation of silver into a range of hygiene and healthcare applications has increased, and this has raised concerns over the development of silver resistance, toxicity, methods of testing products and evidence of efficacy The published evidence for resistance and toxicity is limited and associated with frequent and high levels of silver used Increasing evidence of improved antimicrobial activity of nanoparticles of silver and possible dual immunomodulatory effects are exciting This may lead to further product development as potential alternative preservatives as some currently available preservatives have an increasing incidence of allergic reactions Acknowledging the role of the carrier is important, and as silver is active when in solution, opens a window of opportunity in personal hygiene area This is important in an age when multiple antibiotic-resistant bacteria are becoming prevalent

Pseudomonas fluorescens and closely-related fluorescent pseudomonads as biocontrol agents of soil-borne phytopathogens.

Abstract: Many strains of Pseudomonas fluorescens show potential for biological control of phytopathogens especially root pathogens. In taxonomic terms, several of them are indeed P. fluorescens sensu stricto, while others belong in fact to neighbouring species of the ‘P. fluorescens’ complex or to ill-defined related species within the fluorescent Pseudomonas spp. These bacteria have become prominent models for rhizosphere ecological studies and analysis of bacterial secondary metabolism, and in recent years knowledge on their plant-beneficial traits has been considerably enhanced by widening the focus beyond the case of phytopathogen-directed antagonism. Current genomic analyses of rhizosphere competence and biocontrol traits will likely lead to the development of novel tools for effective management of indigenous and inoculated P. fluorescens biocontrol agents and a better exploitation of their plant-beneficial properties for sustainable agriculture.

Assessment of the bacterial diversity of breast milk of healthy women by quantitative real-time PCR.

Abstract: Aims: Breast milk has been described as a source of bacteria influencing the development of the infant gut microbiota. Up to the present, few studies have been focused on the application of culture-independent techniques to study bacterial diversity in breast milk. In this context, the aim of this study was to characterize the breast milk microbiota of healthy women by applying the quantitative real-time PCR technique (qRTi-PCR). Methods and Results: A total of 50 breast milk samples were analysed by qPCR to assess the presence of different bacterial genera or clusters, including the Bifidobacterium, Lactobacillus, Staphylococcus, Bacteroides, Enterococcus, Streptococcus, Clostridium cluster IV and Clostridium cluster XIVa–XIVb groups. Staphylococcus, Streptococcus, Bifidobacterium and Lactobacillus were the predominant groups and were detected in all the samples. Clostridium XIVa–XIVb and Enterococcus were detected in most of the samples in contrast to the Bacteroides and Clostridium cluster IV groups. Conclusions: Our results confirm the abundance of bacterial DNA in breast milk samples and suggest that the qRTi-PCR technique has a huge potential in the microbiological analysis of human milk. Significance and Impact of the study: qRTi-PCR allowed the detection of bacterial DNA of streptococci, staphylococci, lactic acid bacteria and bifidobacteria in the samples of human milk, which confirms that breast milk can be an important source of bacteria and bacterial DNA to the infant gut.

Bacterial spoilage of wine and approaches to minimize it.

Abstract: Bacteria are part of the natural microbial ecosystem of wine and play an important role in winemaking by reducing wine acidity and contributing to aroma and flavour. Conversely, they can cause numerous unwelcome wine spoilage problems, which reduce wine quality and value. Lactic acid bacteria, especially Oenococcus oeni, contribute positively to wine sensory characters, but other species, such as Lactobacillus sp. and Pediococcus sp can produce undesirable volatile compounds. Consequences of bacterial wine spoilage include mousy taint, bitterness, geranium notes, volatile acidity, oily and slimy-texture, and overt buttery characters. Management of wine spoilage bacteria can be as simple as manipulating wine acidity or adding sulfur dioxide. However, to control the more recalcitrant bacteria, several other technologies can be explored including pulsed electric fields, ultrahigh pressure, ultrasound or UV irradiation, and natural products, including bacteriocins and lysozyme.

Microbial inactivation using plasma-activated water obtained by gliding electric discharges.

Abstract: Aim: To evaluate the microbial disinfection efficacy of a plasmachemical solution obtained by the activation of water with gliding electric discharges. Methods and Results: Distilled water was activated for 5 min by a nonthermal quenched plasma of the glidarc type operating in humid air and at atmospheric pressure. The plasma-activated water (PAW) was then used to treat planktonic and adherent cells of Staphylococcus epidermidis, Leuconostoc mesenteroides (as models of Gram-positive bacteria), Hafnia alvei (a Gram-negative bacteria) and Saccharomyces cerevisiae (as a yeast model). The treatments were less efficient on adherent cells than on planktonic cells in the case of bacteria, but not of S. cerevisiae. Inactivation was more effective for bacteria than for the yeast. Conclusions: Significant reductions in microbial populations were achieved in all cases, demonstrating the effectiveness of this new approach to treat contaminated media. Significance and Impact of the Study: PAW is a promising solution with potential application to the decontamination of equipment and surfaces.

The antimicrobial activity of four commercial essential oils in combination with conventional antimicrobials.

Abstract: Aims: Due to the emergence of multi-drug resistance, alternatives to conventional antimicrobial therapy are needed. This study aims to investigate the in vitro pharmacological interactions between essential oils (considered valuable as natural therapeutic treatments) and conventional antimicrobials (ciprofloxacin/amphotericin B) when used in combination. Methods and Results: Interactions of the essential oils (Melaleuca alternifolia, Thymus vulgaris, Mentha piperita and Rosmarinus officinalis) when combined with ciprofloxacin against Staphylococcus aureus indicate mainly antagonistic profiles. When tested against Klebsiella pneumoniae the isobolograms show antagonistic, synergistic and additive interactions depending on the combined ratio. The R. officinalis/ciprofloxacin combination against K. pneumoniae displayed the most favourable synergistic pattern. The interactions of M. alternifolia (tea tree), T. vulgaris (thyme), M. piperita (peppermint) and R. officinalis (rosemary) essential oils with amphotericin B indicate mainly antagonistic profiles when tested against Candida albicans. Conclusion: While a number of interactions show complete antagonism, others show varied (synergistic, additive and/or antagonistic) interactions, thus the efficacy is dependent on the ratio in which the two components co-exist. Significance and Impact of the Study: The predominant antagonistic interactions noted here, suggests that some natural therapies containing essential oils should be used with caution when combined with antibiotics.

Assessment of cell surface properties and adhesion potential of selected probiotic strains

Abstract: Aim: To evaluate the physicochemical cell surface and adhesive properties of selected probiotic strains for human use. Methods and Results: Probiotic strains, Bifidobacterium longum B6, Lactobacillus acidophilus ADH, Lactobacillus paracasei, Lactobacillus rhamnosus GG, Lactobacillus brevis, Lactobacillus casei, Leuconostoc mesenteroides and Pediococcus acidilactici were tested for the physicochemical properties of cell surfaces and the adhesion abilities against foodborne pathogens. Bif. longum B6 (53·6%) and Lact. rhamnosus GG (46·5%) showed the highest hydrophobicity, while the least affinity to xylene was observed in Ped. acidilactici (10·4%). Bifidobacterium longum B6 showed the strongest coaggregation phenotype with Listeria monocytogenes (53·0%), Shigella boydii (42·0%) and Staphylococcus aureus (45·9%). Lactobacillus rhamnosus GG had the strong binding ability to Caco-2 cells and effectively inhibited the adhesion of L. monocytogenes, Salmonella Typhimurium, Sh. boydii and Staph. aureus to Caco-2 cells. The hydrophobicity was highly correlated with coaggregative abilities and competitive inhibition, suggesting a good relationship between in vitro adhesion and in vivo colonization. Conclusion: The results suggest that Bif. longum B6 and Lact. rhamnosus GG can be candidate probiotics available for human consumption. Significance and Impact of the Study: Because the use of probiotic strains has been more concerned with their beneficial effects in the GI tract, it is essential to examine the potential of probiotic strains based on the physicochemical properties in terms of bacterial-binding and adhesion capabilities.

Auxin production by plant associated bacteria: impact on endogenous IAA content and growth of Triticum aestivum L.

Abstract: Aims: The aim of this study was to investigate the potential of bacterial strains of Bacillus, Pseudomonas, Escherichia, Micrococcus and Staphylococcus genera associated with wild herbaceous flora to enhance endogenous indole-3-acetic acid (IAA) content and growth of Triticum aestivum var. Inqalab-91. Methods and Results: Gas chromatography and mass spectrometric (GC–MS) analysis revealed that bacterial strains produced 0·6–8·22 μg IAA ml−1 in the presence of L-tryptophan. Plant microbe experiments showed a significant positive correlation between auxin production by bacterial strains and endogenous IAA content of T. aestivum for GC–MS (r = 0·618; P = 0.05) and colorimetric analysis (r = 0·693; P = 0.01). Similarly, highly significant positive correlation for shoot length (r = 0·627; P = 0.01) and shoot fresh weight (r = 0·626; P = 0.01) was observed with auxin production under axenic conditions. Bacterial inoculations also enhanced shoot length (up to 29·16%), number of tillers (up to 97·35%), spike length (up to 25·20%) and seed weight (up to 13·70%) at final harvest. Conclusions: Bacterial strains have the ability to increase the endogenous IAA content and growth of T. aestivum var. Inqalab-91. Significance and Impact of the Study: Microbial strains of wild herbaceous flora can be effectively used to enhance the growth and yield of agronomically important crops.

Endophytic bacterial flora in root and stem tissues of black pepper (Piper nigrum L.) genotype: isolation, identification and evaluation against Phytophthora capsici.

Abstract: Aim: To isolate and identify black pepper (Piper nigrum L) associated endophytic bacteria antagonistic to Phytophthora capsici causing foot rot disease. Methods and Results: Endophytic bacteria (74) were isolated, characterized and evaluated against P. capsici. Six genera belong to Pseudomonas spp (20 strains), Serratia (1 strain), Bacillus spp. (22 strains), Arthrobacter spp. (15 strains), Micrococcus spp. (7 strains), Curtobacterium sp. (1 strain) and eight unidentified strains were isolated from internal tissues of root and stem. Three isolates, IISRBP 35, IISRBP 25 and IISRBP 17 were found effective for Phytophthora suppression in multilevel screening assays which recorded over 70% disease suppression in green house trials. A species closest match (99% similarity) of IISRBP 35 was established as Pseudomonas aeruginosa (Pseudomonas EF568931), IISRBP 25 as P. putida (Pseudomonas EF568932), and IISRBP 17 as Bacillus megaterium (B. megaterium EU071712) based on 16S rDNA sequencing. Conclusion: Black pepper associated P. aeruginosa, P. putida and B. megaterium were identified as effective antagonistic endophytes for biological control of Phytophthora foot rot in black pepper. Significance and Impact of the Study: This work provides the first evidence for endophytic bacterial diversity in black pepper stem and roots, with biocontrol potential against P. capsici infection.

Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper

Abstract: Aims: To compare silver and copper, metals with known antimicrobial properties, by evaluating the effects of temperature and humidity on efficacy by challenging with methicillin resistant Staphylococcus aureus (MRSA). Methods and Results: Using standard methodology described in a globally used Japanese Industrial Standard, JIS Z 2801, a silver ion-containing material exhibited >5 log reduction in MRSA viability after 24 h at >90% relative humidity (RH) at 20� C and 35� C but only a 5 log reductions under all test conditions. Conclusions: While the high humidity (>90% RH) and high temperature (35� C) utilized in JIS Z 2801 produce measurable efficacy in a silver ion-containing material, it showed no significant response at lower temperature and humidity levels typical of indoor environments. Significance and Impact of the Study: The high efficacy levels displayed by the copper alloys, at temperature and humidity levels typical of indoor environments, compared to the low efficacy of the silver ion-containing material under the same conditions, favours the use of copper alloys as antimicrobial materials in indoor environments such as hospitals.

Issues in determining factors influencing bacterial attachment: a review using the attachment of Escherichia coli to abiotic surfaces as an example

Abstract: An understanding of the mechanisms which facilitate the attachment of Escherichia coli and other bacterial species to abiotic surfaces is desired by numerous industries including the food and medical industries. Numerous studies have attempted to explain bacterial attachment as a function of bacterial properties such as cellular surface charge, hydrophobicity and outer membrane proteins amongst others. Conflicting evidence in the literature both for and against a positive relationship may arise from the nature of the test methods used to measure them. A handful of recent studies utilizing technologies such as atomic force microscopy have begun to look at bacterial attachment at a single cell and molecular level. These studies may provide the information required to fully understand the underlying factors which influence bacterial cell attachment to abiotic surfaces. A number of issues in determining the influential factors of bacterial attachment have been identified from the literature: a lack of standardization and sensitivity of methods, as well as the value of measuring bulk properties of a number of cells rather than the behaviour of single cells which may overlook key interactions at a molecular level. These issues will need to be addressed in future studies in this area.

Comparison of in vitro models to study bacterial adhesion to the intestinal epithelium

Abstract: Aims: To evaluate the adhesion ability of intestinal bacteria to different in vitro models of intestinal epithelia, and to estimate the suitability of these models and the type of interactions involved. Methods and results: The adhesion of probiotic (Lactobacillus rhamnosus GG and Bifidobacterium animalis subsp. lactis Bb12), commensal (B. animalis IATA-A2 and B. bifidum IATA-ES2) and potentially pathogenic bacteria (E. coli and L. monocytogenes) was determined. The adhesion models used were polycarbonate-well plates, with or without mucin, and different configurations of Caco-2 and/or HT29-MTX cell cultures. All bacteria adhered to wells without mucin (2·6–27·3%), the values being highly variable depending on the bacterial strain. Adhesion percentages of potentially probiotic bacteria to Caco-2 cultures were remarkably lower (P < 0·05) than those to mucin, and more similar to those of pathogenic strains. The lowest adhesion of different bacterial strains was detected on HT29-MTX (0·5–2·3%) cultures and Caco-2/HT29-MTX (0·6–3·2%) cocultures, while these values were increased in Caco-2 cultures plus mucin. Conclusions: The results suggested that bacterial strains exhibit different capacities to adhere to cellular components and several types of mucin present in different models, showing preferences for intestinal MUC2. Significance and impact of the study: The use of Caco-2 cells monolayer plus mucin (type II) better approaches the physiological characteristics of in vivo situation, providing a reliable and suitable in vitro model to evaluate bacterial adhesion.

Factors affecting the production of Trichoderma harzianum secondary metabolites during the interaction with different plant pathogens

Abstract: Aims: Strains of Trichoderma spp. produce numerous bioactive secondary metabolites. The in vitro production and antibiotic activities of the major compounds synthesized by Trichoderma harzianum strains T22 and T39 against Leptosphaeria maculans, Phytophthora cinnamomi and Botrytis cinerea were evaluated. Moreover, the eliciting effect of viable or nonviable biomasses of Rhizoctonia solani, Pythium ultimum or B. cinerea on the in vitro production of these metabolites was also investigated. Methods and Results: T22azaphilone, 1-hydroxy-3-methyl-anthraquinone, 1,8-dihydroxy-3-methyl-anthraquinone, T39butenolide, harzianolide, harzianopyridone were purified, characterized and used as standards. In antifungal assays, T22azaphilone and harzianopyridone inhibited the growth of the pathogens tested even at low doses (1–10 μg per plug), while high concentrations of T39butenolide and harzianolide were needed (>100 μg per plug) for inhibition. The in vitro accumulation of these metabolites was quantified by LC/MS. T22azaphilone production was not enhanced by the presence of the tested pathogens, despite its antibiotic activity. On the other hand, the anthraquinones, which showed no pathogen inhibition, were stimulated by the presence of P. ultimum. The production of T39butenolide was significantly enhanced by co-cultivation with R. solani or B. cinerea. Similarly, viable and nonviable biomasses of R. solani or B. cinerea increased the accumulation of harzianopyridone. Finally, harzianolide was not detected in any of the interactions examined. Conclusions: The secondary metabolites analysed in this study showed different levels of antibiotic activity. Their production in vitro varied in relation to: (i) the specific compound; (ii) the phytopathogen used for the elicitation; (iii) the viability of the elicitor; and (iv) the balance between elicited biosynthesis and biotransformation rates. Significance and Impact of the Study: The use of cultures of phytopathogens to enhance yields of Trichoderma metabolites could improve the production and application of novel biopesticides and biofertilizers based on the active compounds instead of the living microbe. This could have a significant beneficial impact on the management of diseases in crop plants.

Improved treatment of vulvovaginal candidiasis with fluconazole plus probiotic Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14

Abstract: Aims: To determine the ability of probiotic lactobacilli to improve the treatment of vulvovaginal candidiasis (VVC) using a randomized, double-blind and placebo-controlled trial. Methods and Results: Fifty-five women diagnosed with VVC by vaginal discharge positive for Candida spp. (according to culture method) associated with at least one of the symptoms (itching and burning vaginal feeling, dyspareunia and dysuria), were treated with single dose of fluconazole (150 mg) supplemented every morning for the following 4 weeks with two placebo or two probiotic capsules (containing Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14). At 4 weeks, the probiotic treated group showed significantly less vaginal discharge associated with any of the above mentioned symptoms (10·3%vs 34·6%; P = 0·03) and lower presence of yeast detected by culture (10·3%vs 38·5%; P = 0·014). Conclusion: This study has shown that probiotic lactobacilli can increase the effectiveness of an anti-fungal pharmaceutical agent in curing disease. Significance and Impact of the Study: This novel finding of probiotic lactobacilli augmenting the cure rate of yeast vaginitis, not only offers an alternative approach to a highly prevalent condition that adversely affects the quality of life of women around the world, but also raises the question of how this combination works.

Re‐interpretation of the logistic equation for batch microbial growth in relation to Monod kinetics

Abstract: Aims: To determine the underlying substrate utilization mechanism in the logistic equation for batch microbial growth by revealing the relationship between the logistic and Monod kinetics. Also, to determine the logistic rate constant in terms of Monod kinetic constants. Methods and Results: The logistic equation used to describe batch microbial growth was related to the Monod kinetics and found to be first-order in terms of the substrate and biomass concentrations. The logistic equation constant was also related to the Monod kinetic constants. Similarly, the substrate utilization kinetic equations were derived by using the logistic growth equation and related to the Monod kinetics. Conclusion: It is revaled that the logistic growth equation is a special form of the Monod growth kinetics when substrate limitation is first-order with respect to the substrate concentration. The logistic rate constant (k) is directly proportional to the maximum specific growth rate constant (lm) and initial substrate concentration (S0) and also inversely related to the saturation constant (Ks). Significance and Impact of the Study: The semi-empirical logistic equation can be used instead of Monod kinetics at low substrate concentrations to describe batch microbial growth using the relationship between the logistic rate constant and the Monod kinetic constants.

Mechanism of insoluble phosphate solubilization by Pseudomonas fluorescens RAF15 isolated from ginseng rhizosphere and its plant growth-promoting activities.

Abstract: Aims: To investigate the mechanism of insoluble phosphate (P) solubilization and plant growth-promoting activity by Pseudomonas fluorescens RAF15. Methods and Results: We investigated the ability of Ps. fluorescens RAF15 to solubilize insoluble P via two possible mechanisms: proton excretion by ammonium assimilation and organic acid production. There were no clear differences in pH and P solubilization between glucose-ammonium and glucose-nitrate media. P solubilization was significantly promoted with glucose compared to fructose. Regardless of nitrogen sources used, Ps. fluorescens RAF15 solubilized little insoluble P with fructose. High performance liquid chromatography analysis showed that Ps. fluorescens RAF15 produced mainly gluconic and tartaric acids with small amounts of 2-ketogluconic, formic and acetic acids. During the culture, the pH was reduced with increase in gluconic acid concentration and was inversely correlated with soluble P concentration. Ps. fluorescens RAF1 showed the properties related to plant growth promotion: pectinase, protease, lipase, siderophore, hydrogen cyanide, and indoleacetic acid. Conclusion: This study indicated that the P solubility was directly correlated with the organic acids produced. Significance and Impact of the Study: Pseudomonas fluorescens RAF15 possessed different traits related to plant growth promotion. Therefore, Ps. fluorescens RAF15 could be a potential candidate for the development of biofertilizer or biocontrol agent.

Quorum sensing inhibition activity of garlic extract and p-coumaric acid.

Abstract: Aims: The goal of this work was to investigate the influence of DMSO, garlic extract and p-coumaric acid on bacterial quorum sensing (QS). Methods and Results: The decreases in the QS responses of QS reporter strains Escherichia coli pSB401 and pSB536, Agrobacterium tumefaciens NTL4, Chromobacterium violaceum 5999 and wt 494, Pseudomonas putida IsoF/gfp and environmental Pseudomonas chlororaphis were quantified in relation to growth inhibitory effects. DMSO showed no significant QS-specific effects on the strains tested even at close-to-lethal concentrations. Garlic extracts antagonized the activity of QS receptors LuxR, AhyR and TraR, but were toxic at higher concentrations. P-coumaric acid fully inhibited QS responses of 5999, NTL4 and P. chlororaphis, with no influence on cell viability. Conclusions: The quorum sensing inhibition activity of garlic was extended to novel receptors, and p-coumaric acid was found to possess previously undescribed QS antagonist properties. Significance and Impact of the Study: The results suggest that p-coumaric acid might act as QS inhibitor. Further studies are required to understand its role in the regulation of QS and investigate structurally related compounds.

Antibacterial activity of silver nanoparticles (AgNps) synthesized by tea leaf extracts against pathogenic Vibrio harveyi and its protective efficacy on juvenile Feneropenaeus indicus.

Abstract: Aims: To determine the antibacterial potential of silver nanoparticles (AgNps) synthesized by tea leaf extract against Vibrio harveyi and its protective effect on juvenile Feneropenaeus indicus. Methods and Results: AgNps were synthesized by a simple procedure using tea leaf extract as the reducing agent. Bacteriological tests were performed in Luria–Bertani medium on solid agar plates and in liquid systems supplemented with V. harveyi against different concentrations of AgNps. AgNps synthesized in the present study were shown to be effective against V. harveyi isolated from F. indicus. The combined results of long- and short-term treatment of AgNps synthesized by tea leaf extract showed a 71% reduction in accumulated mortality. Conclusions: The long-term administration of AgNps synthesized by tea leaf extracts at the concentration of 10 μg significantly reduced the mortalities in F. indicus from V. harveyi infections. Significance and Impact of the Study: The AgNps synthesized by tea leaf extract may be an alternative to antibiotics in controlling V. harveyi infections.

Sterilization effect of atmospheric plasma on Escherichia coli and Bacillus subtilis endospores

Abstract: Aims: Escherichia coli and Bacillus subtilis spores were treated with an atmospheric plasma mixture created by the ionization of helium and oxygen to investigate the inactivation efficiency of a low-temperature plasma below 70°C. Methods and results: An electrical discharge plasma was produced at a radio frequency (RF) of 13·56 MHz, connected to a perforated circular electrode with a discharge spacing of 1–15 mm. The discharge gas was helium with 0–2% oxygen. For the plasma treatment, a dried E. coli cell or B. subtilis endospore suspension on a cover-glass was exposed to oxygen downstream of the plasma from holes in an RF-powered electrode. The sterilization effect of the RF plasma was highest with 0·2% oxygen, corresponding to the maximum production of oxygen radicals. Conclusions: Oxygen radicals generated by RF plasma are effective for the destruction of bacterial cells and endospores. Significance and Impact of the study: Low-temperature atmospheric plasma can be used for the disinfection of diverse objects, especially for the inactivation of bacterial endospores.

Optimization and biochemical characterization of a bacteriocin from a newly isolated Bacillus subtilis strain 14B for biocontrol of Agrobacterium spp. strains.

Abstract: Aims: The identification of a new compound active against Agrobacterium tumefaciens. Methods and Results: The culture conditions of a newly isolated Bacillus subtilis strain, designed 14B, were optimized, as a first step, to produce its bacteriocin (termed Bac 14B) for the biocontrol of Agrobacterium spp., the causal agents of the crown gall disease. Bac 14B was then partially purified and biochemically characterized. Bacillus subtilis 14B was observed to produce an antibacterial compound having a protinaceous nature. As estimated by sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE), the semi-purified bacteriocin substance was found to be a monomeric protein with a molecular weight of 21 kDa. While the latter’s antimicrobial activity was completely stable during exposure to a temperature range of up to 100� C for 2 h, its initial activity was totally lost at 121� C for 20 min. The maximum bacteriocin production (4096 AU ml )1 ) was recorded after 96 h-incubation in an optimized Luria Bertani medium supplemented with 10 g l )1 glucose, 15 g l )1 K2HPO4 and 5 g l )1 MgSO4 7H2 Oa t 30� C in a shaking flask culture. Interestingly, the B. subtilis 14B culture supernatant that contained the bacteriocin under study was proved efficient in reducing both the percentage of galled plants and the number of galls in tomato. Conclusion: The findings revealed that B. subtilis 14B and its bacteriocin are efficient in reducing the percentage of infections in plants caused by Ag. tumefaciens. Significance and Impact of the Study: The results could be useful for the nurserymen who are particularly interested in the biocontrol of the crown gall disease.

In vitro antiviral activity of Melaleuca alternifolia essential oil.

Abstract: Aims: To investigate the in vitro antiviral activity of Melaleuca alternifolia essential oil (TTO) and its main components, terpinen-4-ol, α-terpinene, γ-terpinene, p-cymene, terpinolene and α-terpineol. Methods and Results: The antiviral activity of tested compounds was evaluated against polio type 1, ECHO 9, Coxsackie B1, adeno type 2, herpes simplex (HSV) type 1 and 2 viruses by 50% plaque reduction assay. The anti-influenza virus assay was based on the inhibition of the virus-induced cytopathogenicity. Results obtained from our screening demonstrated that the TTO and some of its components (the terpinen-4-ol, the terpinolene, the α-terpineol) have an inhibitory effect on influenza A/PR/8 virus subtype H1N1 replication at doses below the cytotoxic dose. The ID50 value of the TTO was found to be 0·0006% (v/v) and was much lower than its CD50 (0·025% v/v). All the compounds were ineffective against polio 1, adeno 2, ECHO 9, Coxsackie B1, HSV-1 and HSV-2. None of the tested compounds showed virucidal activity. Only a slight virucidal effect was observed for TTO (0·125% v/v) against HSV-1 and HSV-2. Conclusions: These data show that TTO has an antiviral activity against influenza A/PR/8 virus subtype H1N1 and that antiviral activity has been principally attributed to terpinen-4-ol, the main active component. Significance and Impact of the Study: TTO should be a promising drug in the treatment of influenza virus infection.

Nisin F in the treatment of respiratory tract infections caused by Staphylococcus aureus

Abstract: Aims: To determine the antimicrobial activity of nisin F against Staphylococcus aureus in the respiratory tract. Methods and Results: The respiratory tract of nonimmunosuppressed and immunosuppressed Wistar rats were colonized with 4 × 105 viable cells of S. aureus K and then treated by administering 8192 arbitrary units (AU) nisin F intranasal. Symptoms of pneumonia were detected in the trachea and lungs of immunosuppressed rats that had not been treated with nisin F. The trachea and lungs of immunosuppressed rats treated with nisin F were healthy. No significant differences were recorded in blood cell indices. The antimicrobial activity of low concentrations nisin F (80–320 AU ml−1) was slightly stimulated by lysozyme and lactoferrin. Conclusions: Nisin F inhibited the growth of S. aureus K in the respiratory tract of immunocompromised rats. Treatment with nisin F at 8192 AU proofed safe, as the trachea, lungs, bronchi and haematology of the rats appeared normal. Significance and Impact of the Study: Nisin F is nontoxic and may be used to control respiratory tract infections caused by S. aureus. This is, however, a preliminary study with an animal model and need to be confirmed with studies on humans.

Technological properties of Oenococcus oeni strains isolated from typical southern Italian wines

Abstract: Aims: To isolate indigenous Oenococcus oeni strains suitable as starters for malolactic fermentation (MLF), using a reliable polyphasic approach. Methods and Results: Oenococcus oeni strains were isolated from Nero di Troia wines undergoing spontaneous MLF. Samples were taken at the end of alcoholic fermentation and during MLF. Wine samples were diluted in a sterile physiological solution and plated on MRS and on modified FT80. Identification of O. oeni strains was performed by a polymerase chain reaction (PCR) experiment using strain-specific primers. Strains were further grouped using a multiplex RAPD-PCR analysis. Then, six strains were inoculated in two wine-like media with two different ethanol concentrations (11 and 13% vol/vol) with a view to evaluate their capacity to grow and to perform MLF. In addition, a quantitative PCR (qRT-PCR) approach was adapted to monitor the physiological state of the strains selected. Conclusion: A positive correlation between the malolactic activity performance and the ability to develop and tolerate stress conditions was observed for two selected O. oeni strains. Significance and Impact of the Study: The results reported are useful for the selection of indigenous MLF starter cultures with desired oenological traits from typical regional wines. It should be the base for the improvement in organoleptic quality of typical red wine.

Effect of culture medium and cryoprotectants on the growth and survival of probiotic lactobacilli during freeze drying.

Abstract: Aims: To investigate the effects of the medium and cryoprotective agents used on the growth and survival of Lactobacillus plantarum and Lactobacillus rhamnosus GG during freeze drying. Methods and Results: A complex medium was developed consisting primarily of glucose, yeast extract and vegetable-derived peptone. Trehalose, sucrose and sorbitol were examined for their ability to protect the cells during freeze drying. Using standardized amount of cells and the optimized freeze drying media, the effect of the growth medium on cell survival during freeze drying was investigated. The results showed that glucose and yeast extract were the most important growth factors, while sucrose offered better protection than trehalose and sorbitol during freeze drying. When the cells were grown under carbon limiting conditions, their survival during freeze drying was significantly decreased. Conclusions: A clear relationship was observed between cell growth and the ability of the cells to survive during the freeze drying process. Significance and Impact of the Study: The survival of probiotic strains during freeze drying was shown to be dependent on the cryoprotectant used and the growth medium.

Biosurfactant production by Pseudomonas sp. and its role in aqueous phase partitioning and biodegradation of chlorpyrifos.

Abstract: Aim: To study the effect of biosurfactant on aqueous phase solubility and biodegradation of chlorpyrifos. Methods and Results: A Pseudomonas sp. (ChlD), isolated from agricultural soil by enrichment culture technique in the presence of chlorpyrifos, was capable of producing biosurfactant (rhamnolipids) and degrading chlorpyrifos (0·01 g l−1). The partially purified rhamnolipid biosurfactant preparation, having a CMC of 0·2 g l−1, was evaluated for its ability to enhance aqueous phase partitioning and degradation of chlorpyrifos (0·01 g l−1) by ChlD strain. The best degradation efficiency was observed at 0·1 g l−1 supplement of biosurfactant, as validated by GC and HPLC studies. Conclusion: The addition of biosurfactant at 0·1 g l−1 resulted in more than 98% degradation of chlorpyrifos when compared to 84% in the absence of biosurfactant after 120-h incubation. Significance and Impact of the Study: This first report, to the best of our knowledge, on enhanced degradation of chlorpyrifos in the presence of biosurfactant(s), would help in developing bioremediation protocols to counter accumulation of organophosphates to toxic/carcinogenic levels in environment.

Surfactin reduces the adhesion of food-borne pathogenic bacteria to solid surfaces.

Abstract: Aims: To investigate the effect of the biosurfactants surfactin and rhamnolipids on the adhesion of the food pathogens Listeria monocytogenes, Enterobacter sakazakii and Salmonella Enteritidis to stainless steel and polypropylene surfaces. Methods and Results: Quantification of bacterial adhesion was performed using the crystal violet staining technique. Preconditioning of surfaces with surfactin caused a reduction on the number of adhered cells of Ent. sakazakii and L. monocytogenes on stainless steel. The most significant result was obtained with L. monocytogenes where number of adhered cells was reduced by 102 CFU cm−2. On polypropylene, surfactin showed a significant decrease on the adhesion of all strains. The adsorption of surfactin on polystyrene also reduces the adhesion of L. monocytogenes and Salm. Enteritidis growing cells. For short contact periods using nongrowing cells or longer contact periods with growing cells, surfactin was able to delay bacterial adhesion. Conclusions: The prior adsorption of surfactin to solid surfaces contributes on reducing colonization of the pathogenic bacteria. Significance and Impact of the Study: This is the first work investigating the effect of surfactin on the adhesion of the food pathogens L. monocytogenes, Ent. sakazakii and Salm. Enteritidis to polypropylene and stainless steel surfaces.

Bacterial contamination on touch surfaces in the public transport system and in public areas of a hospital in London

Abstract: Aims: To investigate bacterial contamination on hand-touch surfaces in the public transport system and in public areas of a hospital in central London. Methods and Results: Dipslides were used to sample 118 hand-touch surfaces in buses, trains, stations, hotels and public areas of a hospital in central London. Total aerobic counts were determined, and Staphylococcus aureus isolates were identified and characterized. Bacteria were cultured from 112 (95%) of sites at a median concentration of 12 CFU cm−2. Methicillin-susceptible Staph. aureus (MSSA) was cultured from nine (8%) of sites; no sites grew methicillin-resistant Staph. aureus (MRSA). Conclusions: Hand-touch sites in London are frequently contaminated with bacteria and can harbour MSSA, but none of the sites tested were contaminated with MRSA. Significance and Impact of the Study: Hand-touch sites can become contaminated with staphylococci and may be fomites for the transmission of bacteria between humans. Such sites could provide a reservoir for community-associated MRSA (CA-MRSA) in high prevalence areas but were not present in London, a geographical area with a low incidence of CA-MRSA.