Secondary metabolite profile of Streptomyces spp. changes when grown with the sub-lethal concentration of silver nanoparticles: possible implication in novel compound discovery.

The decline of new antibiotics and the emergence of multidrug resistance in pathogens necessitates a revisit of strategies used for lead compound discovery. This study proposes to induce the production of bioactive compounds with sub-lethal concentrations of silver nanoparticles (Ag-NPs). A total of Forty-two Actinobacteria isolates from four Saudi soil samples were grown with and without sub-lethal concentration of Ag-NPs (50 µg ml-1). The spent broth grown with Ag-NPs, or without Ag-NPs were screened for antimicrobial activity against four bacteria. Interestingly, out of 42 strains, broths of three strains grown with sub-lethal concentration of Ag-NPs exhibit antimicrobial activity against Staphylococcus aureus and Micrococcus luteus. Among these, two strains S4-4 and S4-21 identified as Streptomyces labedae and Streptomyces tirandamycinicus based on 16S rRNA gene sequence were selected for detailed study. The change in the secondary metabolites profile in the presence of Ag-NPs was evaluated using GC-MS and LC-MS analyses. Butanol extracts of spent broth grown with Ag-NPs exhibit strong antimicrobial activity against M. luteus and S. aureus. While the extracts of the controls with the same concentration of Ag-NPs do not show any activity. GC-analysis revealed a clear change in the secondary metabolite profile when grown with Ag-NPs. Similarly, the LC-MS patterns also differ significantly. Results of this study, strongly suggest that sub-lethal concentrations of Ag-NPs influence the production of secondary metabolites by Streptomyces. Besides, LC-MS results identified possible secondary metabolites, associated with oxidative stress and antimicrobial activities. This strategy can be used to possibly induce cryptic biosynthetic gene clusters for the discovery of new lead compounds.

Zn solubilizing bacteria (ZSB) mitigate toxicity of silver and Titanium dioxide nanoparticles in Mung bean by increasing photosynthetic pigment content.

Zn-deficiency, a global health challenge affects one-third of the world population. Zn-biofertilizer offer an efficient and cost-effective remedy. As Zn-biofertilizer can improve plant growth and grain's Zn-content ensuring improved dietary Zn-supply. This study sought to understand how silver and TiO2 nanoparticles in the rhizosphere affect the activity of Zn-solubilization bacteria (ZSB) and plant growth. Two ZSB strains Bacillus sp. D-7 and Pseudomonas sp. D-117 with excellent Zn-solubilization efficiency of 254 and 260%, respectively were isolated and characterized using polyphasic characterization including 16S rRNA gene sequencing to formulate an effective Zn-biofertilizer. The plant growth promoting activity of this biofertilizer in Mung bean was checked in the presence and absence of various doses of TiO2 and Ag-NPs and was compared with plant grown without biofertilizer. The change in rate of seed germination, vegetative growth (shoot and root length, fresh and dry weight), photosynthetic pigment and Zn-content was checked. Lower doses of nanomaterials (50 and 100 mg kg⁻¹ soil) slightly promoted the plant growth compared to control. While, higher doses (200 and 400 mg kg⁻¹ soil) inhibited the growth. A maximum decrease of shoot length, root length, fresh-weight, and dry-weight of 57.1, 53.9, 53.1, and 10.4% respectively was observed with 400 mg kg⁻¹ of Ag-NPs. However, in the presence of ZSB, the decrease at the same Ag-NP concentration was 41.6, 31.5, 27.4, and 6.6, respectively. These results strongly suggest that Zn-solubilizing bacteria improve resilience to nanoparticles toxicity and helps in Zn fortification in Mung bean even under nanomaterial stress.

Indigenously produced biochar retains fertility in sandy soil through unique microbial diversity sustenance: a step toward the circular economy.

Introduction: Agricultural productivity in the arid hot desert climate of UAE is limited by the unavailability of water, high temperature, and salt stresses. Growing enough food under abiotic stresses and decreasing reliance on imports in an era of global warming are a challenge. Biochar with high water and nutrient retention capacity and acid neutralization activity is an attractive soil conditioner. This study investigates the microbial community in the arid soil of Dubai under shade house conditions irrigated with saline water and the shift in the microbial community, following 1 year of amendment with indigenously prepared biochar from date palm waste. Methods: Amplicon sequencing was used to elucidate changes in bacterial, archaeal, and fungal community structures in response to long-term biochar amendment. Samples were collected from quinoa fields receiving standard NPK doses and from fields receiving 20 and 30 tons ha-1 of biochar, in addition to NPK for 1 year. Water holding capacity, pH, electrical conductivity, calcium, magnesium, chloride, potassium, sodium, phosphorus, total carbon, organic matter, and total nitrogen in the soil from biochar-treated and untreated controls were determined. Results and discussion: The results show that soil amendment with biochar helps retain archaeal and bacterial diversity. Analysis of differentially abundant bacterial and fungal genera indicates enrichment of plant growth-promoting microorganisms. Interestingly, many of the abundant genera are known to tolerate salt stress, and some observed genera were of marine origin. Biochar application improved the mineral status and organic matter content of the soil. Various physicochemical properties of soil receiving 30 tons ha-1 of biochar improved significantly over the control soil. This study strongly suggests that biochar helps retain soil fertility through the enrichment of plant growth-promoting microorganisms.

Pulicaria undulata Extract-Mediated Eco-Friendly Preparation of TiO2 Nanoparticles for Photocatalytic Degradation of Methylene Blue and Methyl Orange.

Eco-friendly approaches for the preparation of nanomaterials have recently attracted considerable attention of scientific community due to rising environmental distresses. The aim of the current study is to prepare titanium dioxide (TiO2) nanoparticles (NPs) using an eco-friendly approach and investigate their performance for the photocatalytic degradation of hazardous organic dyes. For this, TiO2 NPs were prepared by using the aqueous extract of the Pulicaria undulata (L.) plant in a single step at room temperature. Energy-dispersive X-ray spectroscopy established the presence of both titanium and oxygen in the sample. X-ray diffraction revealed the formation of crystalline, anatase-phase TiO2 NPs. On the other hand, transmission election microscopy confirmed the formation of spherical shaped NPs. The presence of residual phytomolecules as capping/stabilization agents is confirmed by UV-vis analysis and Fourier-transform Infrared spectroscopy. Indeed, in the presence of P. undulata, the anatase phase of TiO2 is stabilized at a significantly lower temperature (100 °C) without using any external stabilizing agent. The green synthesized TiO2 NPs were used to investigate their potential for the photocatalytic degradation of hazardous organic dyes including methylene blue and methyl orange under UV-visible light irradiation. Due to the small size and high dispersion of NPs, almost complete degradation (∼95%) was achieved in a short period of time (between 1 and 2 h). No significant difference in the photocatalytic activity of the TiO2 NPs was observed even after repeated use (three times) of the photocatalyst. Overall, the green synthesized TiO2 NPs exhibited considerable potential for fast and eco-friendly removal of harmful organic dyes.

Illumina sequencing of 16S rRNA genes reveals a unique microbial community in three anaerobic sludge digesters of Dubai.

Understanding the microbial communities in anaerobic digesters, especially bacteria and archaea, is key to its better operation and regulation. Microbial communities in the anaerobic digesters of the Gulf region where climatic conditions and other factors may impact the incoming feed are not documented. Therefore, Archaeal and Bacterial communities of three full-scale anaerobic digesters, namely AD1, AD3, and AD5 of the Jebel Ali Sewage water Treatment Plant (JASTP) were analyzed by Illumina sequencing of 16S rRNA genes. Among bacteria, the most abundant genus was fermentative bacteria Acetobacteroides (Blvii28). Other predominant bacterial genera in the digesters included thermophilic bacteria (Fervidobacterium and Coprothermobacter) and halophilic bacteria like Haloterrigena and Sediminibacter. This can be correlated with the climatic condition in Dubai, where the bacteria in the incoming feed may be thermophilic or halophilic as much of the water used in the country is desalinated seawater. The predominant Archaea include mainly the members of the phyla Euryarchaeota and Crenarchaeota belonging to the genus Methanocorpusculum, Metallosphaera, Methanocella, and Methanococcus. The highest population of Methanocorpusculum (more than 50% of total Archaea), and other hydrogenotrophic archaea, is in agreement with the high population of bacterial genera Acetobacteroides (Blvii28) and Fervidobacterium, capable of fermenting organic substrates into acetate and H2. Coprothermobacter, which is known to improve protein degradation by establishing syntrophy with hydrogenotrophic archaea, is also one of the digesters' dominant genera. The results suggest that the microbial community in three full-scale anaerobic digesters is different. To best of our knowledge this is the first detailed report from the UAE.

Engineered Nanomaterials in Soil: Their Impact on Soil Microbiome and Plant Health.

A staggering number of nanomaterials-based products are being engineered and produced commercially. Many of these engineered nanomaterials (ENMs) are finally disposed into the soil through various routes in enormous quantities. Nanomaterials are also being specially tailored for their use in agriculture as nano-fertilizers, nano-pesticides, and nano-based biosensors, which is leading to their accumulation in the soil. The presence of ENMs considerably affects the soil microbiome, including the abundance and diversity of microbes. In addition, they also influence crucial microbial processes, such as nitrogen fixation, mineralization, and plant growth promoting activities. ENMs conduct in soil is typically dependent on various properties of ENMs and soil. Among nanoparticles, silver and zinc oxide have been extensively prepared and studied owing to their excellent industrial properties and well-known antimicrobial activities. Therefore, at this stage, it is imperative to understand how these ENMs influence the soil microbiome and related processes. These investigations will provide necessary information to regulate the applications of ENMs for sustainable agriculture and may help in increasing agrarian production. Therefore, this review discusses several such issues.

Enhanced Antimicrobial Activity of Biofunctionalized Zirconia Nanoparticles.

The effective interactions of nanomaterials with biological constituents play a significant role in enhancing their biomedicinal properties. These interactions can be efficiently enhanced by altering the surface properties of nanomaterials. In this study, we demonstrate the method of altering the surface properties of ZrO2 nanoparticles (NPs) to enhance their antimicrobial properties. To do this, the surfaces of the ZrO2 NPs prepared using a solvothermal method is functionalized with glutamic acid, which is an α-amino acid containing both COO- and NH4 + ions. The binding of glutamic acid (GA) on the surface of ZrO2 was confirmed by UV-visible and Fourier transform infrared spectroscopies, whereas the phase and morphology of resulting GA-functionalized ZrO2 (GA-ZrO2) was identified by X-ray diffraction and transmission electron microscopy. GA stabilization has altered the surface charges of the ZrO2, which enhanced the dispersion qualities of NPs in aqueous media. The as-prepared GA-ZrO2 NPs were evaluated for their antibacterial properties toward four strains of oral bacteria, namely, Rothia mucilaginosa, Rothia dentocariosa, Streptococcus mitis, and Streptococcus mutans. GA-ZrO2 exhibited increased antimicrobial activities compared with pristine ZrO2. This improved activity can be attributed to the alteration of surface charges of ZrO2 with GA. Consequently, the dispersion properties of GA-ZrO2 in the aqueous solution have increased considerably, which may have enhanced the interactions between the nanomaterial and bacteria.

Antibiotic and Antibiofilm Activities of Salvadora persica L. Essential Oils against Streptococcus mutans: A Detailed Comparative Study with Chlorhexidine Digluconate.

The use of organic components from plants as an alternative antimicrobial agent is becoming popular due to the development of drug-resistance in various pathogens. Essential oils from fresh (MF-1) and dried (MD-1) roots of Salvadora persica L. were extracted and benzyl isothiocynate was determined as their chief constituent using GC-MS and GC-FID. The antibiofilm and antimicrobial activities of MD-1 and MF-1 against Streptococcus mutans a dental caries causing bacteria were determined using multiple assays. These activities were compared with chlorhexidine digluconate (CHX) and clove oil, well known antimicrobial agents for oral hygiene. Essential oils demonstrated IC50 values (10-11 µg/mL) comparable to that of CHX, showed a significant reduction (82 ± 7-87 ± 6%) of the biofilm formation at a very low concentration. These results were supported by RT-PCR studies showing change in the expression levels of AtlE, gtfB, ymcA and sodA genes involved in autolysis, biofilm formation and oxidative stress, respectively. The results presented in this study show the robust bactericidal and antibiofilm activity of MD-1 and MF-1 against S. mutans which is comparable to Chlorhexidine digluconate. Our results suggest that these essential oils can be as effective as CHX and hence can serve as a good alternative antimicrobial agent for oral hygiene.

Survival of probiotic bacteria in the presence of food grade nanoparticles from chocolates: an in vitro and in vivo study.

The use of probiotics to treat gastrointestinal diseases such as diarrhea especially in children is becoming increasingly popular. Besides, the use of nanomaterials in food products is increasing rapidly especially in candies and chocolates. How these nanomaterials influence probiotic bacteria and their activity remains unexplored. Therefore, nanomaterials from commercial chocolate were purified and characterized by using SEM-EDS and XRD. The tested chocolate contained nano-TiO2 with an average size of ~ 40 nm. The influence of the extracted TiO2 on a commercial probiotic formulation usually used to treat diarrhea in children was studied. The probiotic formulation contained Bacillus coagulans, Enterococcus faecalis, and Enterococcus faecium as evident from 16S rRNA gene sequences and polyphasic characterization. Isolated bacteria exhibited known probiotic activities like biofilm formation, acid production, growth at 6% salt, and antibiotic resistance. TiO2 from chocolates inhibited the growth and activity of the probiotic formulation over a concentration range of 125-500µg/ml in vitro. Based on results, it is estimated that 20 g of such chocolate contains enough TiO2 to disturb the gut microbial community of children aged 2-8 years with a stomach capacity of ~ 0.5-0.9 l. The in vivo study on white albino mice shows the same response but with a higher dose. The results obtained by plate counts, MTT assay, live/dead staining, and qPCR suggest that TiO2 from chocolates inhibits the growth and viability of probiotic bacteria in mice gut even at a concentration of 50-100 µg/day/mice. Therefore, TiO2 in chocolate discourages survival of probiotic bacteria in the human gut.

Engineered nanomaterials for water decontamination and purification: From lab to products.

Clean water is vital for life; it is required not only for drinking but also for the preparation of food and proper hygiene. Unfortunately, more than fifty percent of the world population mainly in China and India face a severe scarcity of water. Around 1.8 billion people inevitably drink water from sources having fecal contamination resulting in the death of about a million children every year. Scientists are developing various economic technologies to decontaminate and purify water. Nanomaterials-based technology offers an economic and effective alternative for water purification and decontamination. As nanomaterials are available globally, have remarkable antimicrobial activity and the ability to effectively remove organic and inorganic pollutants from water. This review discusses the potential role of nanomaterials in the purification of drinking water. As nanomaterials exhibit remarkable antimicrobial and antiparasitic activities against waterborne pathogens and parasites of primary concern like Shigella dysenteriae, Vibrio cholera, and Entamoeba histolytica. Nanomaterials also demonstrate the ability to absorb toxic chemicals like mercury and dyes from polluted water. However, for successful commercialization of the technology, some inherent bottlenecks need to be addressed adequately. These include nanoparticles aggregation, their seepage into drinking water and adverse effects on human health and the environment. Nanocomposites are being developed to overcome these problems and to combine two or more desirable properties for water purification. Widespread and large-scale use of nanomaterials for water purification soon may become a reality. Products containing nanomaterials such as Karofi, Lifestraw, and Tupperware for water purification are already available in the market.

Plant extracts as green reductants for the synthesis of silver nanoparticles: lessons from chemical synthesis.

The increasing use of silver (Ag) nanoparticles (NPs) in daily-life applications, electronics, or catalysis calls for green and cost-efficient synthetic methods. Ag NPs are used especially in biomedicine because of their antibacterial, antifungal, or anticancer properties. Chemical synthesis allows tuning the particle morphology, size, and crystallinity, but requires toxic and hazardous chemicals. Bioinspired synthetic protocols have shown promise to minimize environmental impact, but biological protocols for the synthesis of Ag NPs lack control on the morphology and crystallinity. This review briefly compiles the chemical synthesis of Ag NPs and contrasts it with "green" protocols based on lessons learnt from chemical synthesis. The synthesis of Ag NPs with different plant extracts and the associated phytomolecules, their chemical and biological effects, and their effect on particle synthesis are described and put into perspective to improve green protocols. The surface functionalization of Ag NPs by phytomolecules and the mechanisms of their biomedical applications are summarized.

Sub-lethal doses of widespread nanoparticles promote antifungal activity in Pseudomonas protegens CHA0.

Nanoparticles are widely used as antimicrobial compounds. At sub-lethal concentrations, they may also stress microbes, potentially inducing antibiosis. Here we assess whether nanoparticles can serve as an enhancer of antibiosis in beneficial microbes. Several host-associated bacteria can suppress pathogens, providing therefore a first line of defense against diseases. In the present study, we assessed whether nanoparticles stimulate the antifungal activity of Pseudomonas protegens CHA0, a model plant-associated bacterium, against the ascomycete yeast Candida albicans. We synthesized and characterized four of the most common nanoparticles, namely Ag, SiO2, TiO2, and ZnO, with an average size of 25, 11, 25 and 35 nm, respectively. The dose-dependent effect of these nanoparticles on the growth of Pseudomonas protegens CHA0 was assessed. Ag, SiO2, TiO2, and ZnO nanoparticles inhibited the growth of Pseudomonas protegens by 100, 22, 15 and 15%, respectively at a concentration of 250 µg/mL. We then selected sub-lethal dose (500 ng/mL) and assessed whether the same nanoparticles stimulated the production of antifungal compounds inhibiting C. albicans. Incubating the bacteria in the presence of nanoparticles led to a four-fold increase in antifungal activity. We finally show that nanoparticles induce the expression of the prn operon, responsible for the production of antifungal compound pyrrolnitrin, within hours after nanoparticle exposure. This study shows that nanoparticle application may be a valuable tool to stimulate the antifungal activity of fluorescent pseudomonads, potentially assisting the development of future sustainable disease control strategies.

Spectral and thermal properties of novel eye lens ζ-crystallin.

Eye lenses are exposed to thermal, solar radiations, dryness that enhances cataractogenesis. Some animal lenses contain novel proteins in bulk quantities. ζ-crystallin occurred in three ecologically divergent species, but it's physiological role not known. The truncated variant of ζ-crystallin causes hereditary cataract. Guinea pig ζ-crystallin is temperature-sensitive and rapidly aggregates at 41°C. Camels adopted to survive above 50°C, which raises an interesting question about how it retains lens proteins in the soluble state? Here, we have optimized expression and purification of recombinant camel ζ-crystallin. We have studied thermodynamic and spectroscopic properties using orthogonal techniques. Dynamic multimode spectroscopy results showed that camel ζ-crystallin unfolds via single transition with Tm value of 60.8±0.1°C and van't Hoff enthalpy of 714.7±7.1kJ/mol. Thermal-shift assay calculates Tm value of 62°C at pH 7. Additionally, the conformational stability of ζ-crystallin increases with ionic-strength. The influence of pH on ζ-crystallin was evaluated where the protein was found to be stable in the pH range of 6-9, but its stability drastically decreases below pH 6. Our results also showed that quaternary structure of ζ-crystallin drastically changed as a result of lowering pH. This study provides significant understandings onto the conformational, thermodynamic and unfolding pathway of camel ζ-crystallin.

Thymol and carvacrol induce autolysis, stress, growth inhibition and reduce the biofilm formation by Streptococcus mutans.

Organic compounds from plants are an attractive alternative to conventional antimicrobial agents. Therefore, two compounds namely M-1 and M-2 were purified from Origanum vulgare L. and were identified as carvacrol and thymol, respectively. Antimicrobial and antibiofilm activities of these compounds along with chlorhexidine digluconate using various assays was determined against dental caries causing bacteria Streptococcus mutans. The IC50 values of carvacrol (M-1) and thymol (M-2) against S. mutans were 65 and 54 µg/ml, respectively. Live and dead staining and the MTT assays reveal that a concentration of 100 µg/ml of these compounds reduced the viability and the metabolic activity of S. mutans by more than 50%. Biofilm formation on the surface of polystyrene plates was significantly reduced by M-1 and M-2 at 100 µg/ml as observed under scanning electron microscope and by colorimetric assay. These results were in agreement with RT-PCR studies. Wherein exposure to 25 µg/ml of M-1 and M-2 showed a 2.2 and 2.4-fold increase in Autolysin gene (AtlE) expression level, respectively. While an increase of 1.3 and 1.4 fold was observed in the super oxide dismutase gene (sodA) activity with the same concentrations of M-1 and M-2, respectively. An increase in the ymcA gene and a decrease in the gtfB gene expression levels was observed following the treatment with M-1 and M-2. These results strongly suggest that carvacrol and thymol isolated from O. vulgare L. exhibit good bactericidal and antibiofilm activity against S. mutans and can be used as a green alternative to control dental caries.

"Miswak" Based Green Synthesis of Silver Nanoparticles: Evaluation and Comparison of Their Microbicidal Activities with the Chemical Synthesis.

Microbicidal potential of silver nanoparticles (Ag-NPs) can be drastically improved by improving their solubility or wettability in the aqueous medium. In the present study, we report the synthesis of both green and chemical synthesis of Ag-NPs, and evaluate the effect of the dispersion qualities of as-prepared Ag-NPs from both methods on their antimicrobial activities. The green synthesis of Ag-NPs is carried out by using an aqueous solution of readily available Salvadora persica L. root extract (RE) as a bioreductant. The formation of highly crystalline Ag-NPs was established by various analytical and microscopic techniques. The rich phenolic contents of S. persica L. RE (Miswak) not only promoted the reduction and formation of NPs but they also facilitated the stabilization of the Ag-NPs, which was established by Fourier transform infrared spectroscopy (FT-IR) analysis. Furthermore, the influence of the volume of the RE on the size and the dispersion qualities of the NPs was also evaluated. It was revealed that with increasing the volume of RE the size of the NPs was deteriorated, whereas at lower concentrations of RE smaller size and less aggregated NPs were obtained. During this study, the antimicrobial activities of both chemically and green synthesized Ag-NPs, along with the aqueous RE of S. persica L., were evaluated against various microorganisms. It was observed that the green synthesized Ag-NPs exhibit comparable or slightly higher antibacterial activities than the chemically obtained Ag-NPs.

Countering drug resistance, infectious diseases, and sepsis using metal and metal oxides nanoparticles: Current status.

One fourth of the global mortalities is still caused by microbial infections largely due to the development of resistance against conventional antibiotics among pathogens, the resurgence of old infectious diseases and the emergence of hundreds of new infectious diseases. The lack of funds and resources for the discovery of new antibiotics necessitates the search for economic and effective alternative antimicrobial agents. Metal and metal oxide nanoparticles including silver and zinc oxide exhibit remarkable antimicrobial activities against pathogens and hence are one of the most propitious alternative antimicrobial agents. These engineered nanomaterials are approved by regulatory agencies such as USFDA and Korea's FITI, for use as antimicrobial agents, supplementary antimicrobials, food packaging, skin care products, oral hygiene, and for fortifying devices prone to microbial infections. Nevertheless, detailed studies, on molecular and biochemical mechanisms underlying their antimicrobial activity are missing. To take the full advantage of this emerging technology selective antimicrobial activity of these nanoparticles against pathogens should be studied. Optimization of these nanomaterials through functionalization to increase their efficacy and biocompatibility is also required. Urgent in vivo studies on the toxicity of nanomaterials at realistic doses are also needed before their clinical translation.

Zinc oxide and titanium dioxide nanoparticles induce oxidative stress, inhibit growth, and attenuate biofilm formation activity of Streptococcus mitis.

Streptococcus mitis from the oral cavity causes endocarditis and other systemic infections. Rising resistance against traditional antibiotics amongst oral bacteria further aggravates the problem. Therefore, antimicrobial and antibiofilm activities of zinc oxide and titanium dioxide nanoparticles (NPs) synthesized and characterized during this study against S. mitis ATCC 6249 and Ora-20 were evaluated in search of alternative antimicrobial agents. ZnO and TiO2-NPs exhibited an average size of 35 and 13 nm, respectively. The IC50 values of ZnO and TiO2-NPs against S. mitis ATCC 6249 were 37 and 77 µg ml(-1), respectively, while the IC50 values against S. mitis Ora-20 isolate were 31 and 53 µg ml(-1), respectively. Live and dead staining, biofilm formation on the surface of polystyrene plates, and extracellular polysaccharide production show the same pattern. Exposure to these nanoparticles also shows an increase (26-83 %) in super oxide dismutase (SOD) activity. Three genes, namely bapA1, sodA, and gtfB like genes from these bacteria were identified and sequenced for quantitative real-time PCR analysis. An increase in sodA gene (1.4- to 2.4-folds) levels and a decrease in gtfB gene (0.5- to 0.9-folds) levels in both bacteria following exposure to ZnO and TiO2-NPs were observed. Results presented in this study verify that ZnO-NPs and TiO2-NPs can control the growth and biofilm formation activities of these strains at very low concentration and hence can be used as alternative antimicrobial agents for oral hygiene.

Antibacterial properties of silver nanoparticles synthesized using Pulicaria glutinosa plant extract as a green bioreductant.

The antibacterial properties of nanoparticles (NPs) can be significantly enhanced by increasing the wettability or solubility of NPs in aqueous medium. In this study, we investigated the effects of the stabilizing agent on the solubility of silver NPs and its subsequent effect on their antimicrobial activities. Silver NPs were prepared using an aqueous solution of Pulicaria glutinosa plant extract as bioreductant. The solution also acts as a capping ligand. During this study, the antimicrobial activities of silver NPs, as well as the plant extract alone, were tested against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Micrococcus luteus. Silver NPs were prepared with various concentrations of the plant extract to study its effect on antimicrobial activity. Interestingly, various concentrations of P. glutinosa extract did not show any effect on the growth of tested bacteria; however, a significant effect on the antimicrobial property of plant extract capped silver NPs (Ag-NPs-PE) was observed. For instance, the half maximal inhibitory concentration values were found to decrease (from 4% to 21%) with the increasing concentrations of plant extract used for the synthesis of Ag-NPs-PE. These results clearly indicate that the addition of P. glutinosa extracts enhances the solubility of Ag-NPs-PE and, hence, increases their toxicity against the tested microorganisms.

Comparative effectiveness of NiCl2, Ni- and NiO-NPs in controlling oral bacterial growth and biofilm formation on oral surfaces.

OBJECTIVE: Oral ailments are often treated with antibiotics, which are rendered ineffective as bacteria continue to develop resistance against them. It has been suggested that the nanoparticles (NPs) approach may provide a safer and viable alternative to traditional antibacterial agents. Therefore, nickel (Ni)- and nickel oxide (NiO)-NPs were synthesized, characterized and assessed for their efficacy in reducing oral bacterial load in vitro. Also, the effects of bulk compound NiCl2 (Ni ions), along with the Ni- and NiO-NPs on bacterial exopolysaccharide (EPS) production and biofilm formation on the surface of artificial teeth, and acrylic dentures, were investigated. METHODS: Total bacteria from a healthy male were collected and adjusted to 4×109cells/ml for all the tests. Effect of the NPs on growth, biofilm formation, EPS production and acid production from glucose was tested using standard protocols. RESULTS: Data revealed that the Ni-NPs (average size 41.23nm) exhibited an IC50 value of 73.37µg/ml against total oral bacteria. While, NiO-NPs (average size 35.67nm) were found less effective with much higher IC50 value of 197.18µg/ml. Indeed, the Ni ions exhibited greater biocidal activity with an IC50 value of 70µg/ml. Similar results were obtained with biofilm inhibition on the surfaces of dental prostheses. The results explicitly suggested the effectiveness of tested Ni compounds on the growth of oral bacteria and biofilm formation in the order as NiCl2>Ni-NPs>NiO-NPs. CONCLUSION: The results elucidated that Ni-NPs could serve as effective nanoantibiotics against oral bacteria.

Effective inhibition of bacterial respiration and growth by CuO microspheres composed of thin nanosheets.

This study describes the synthesis, characterization and biocidal potential of copper oxide micro-spheres composed of thin sheets (CuOMSs-Ths). Microscopic observations of synthesized CuOMSs-Ths revealed the clusters of thin sheets arranged in small flower like micro-spheres. Diameter of each micro-sphere was determined in the range of 2-3 µm, whereas the size of each sheet was ∼ 80 nm. These micro-flowers like nanostructures were synthesized using copper nitrate hexahydrate and sodium hydroxide via solution process. The CuOMSs-Ths exhibited a broad-spectrum anti-bacterial activity involving significant growth inhibition of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Micrococcus luteus. The IC50 values of these engineered NPs against E. coli, P. aeruginosa, S. aureus and M. luteus were determined to be 195, 200, 131 and 184 µg/ml, respectively. Also, the respiration of Gram+ ve organisms (M. luteus and S. aureus) was inhibited significantly (p value < 0.005) at relatively lower concentrations of 12.5 and 50 µg/ml, respectively, as compared to the Gram- ve bacteria (E. coli and P. aeruginosa), where the growth inhibition occurred at a much greater concentration of 100 µg/ml. The results explicitly demonstrated anti-microbial activity of CuOMSs-Ths with a higher level of toxicity against the Gram+ ve vis-a-vis Gram- ve bacteria.