Photocatalytic Activity and Antibacterial Effect of Ag3PO4 Powders Against Methicillin-resistant Staphylococcus aureus

In this study, silver phosphate (Ag3PO4) was successfully prepared through a simple precipitation method, and its structural, optical, and morphological properties were characterized by X-ray diffraction, Rietveld refinement, Fourier transform infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, photoluminescence measurements, and field emission scanning electron microscopy (FE-SEM). Thereafter, the photocatalytic activity for the degradation of rhodamine B (RhB) dye and the antibacterial effect against methicillin-resistant Staphylococcus aureus (MRSA) were analyzed. Ag3PO4 was highly photocatalytic, degrading approximately 100% of the RhB after 25 min of visible light exposure. The photocatalytic mechanism was evaluated by trapping experiments indicating that photogenerated holes and superoxide radicals were the principal species present in the photocatalytic system. In addition, Ag3PO4 is a potential bacterial agent as it reduced the MRSA population even at sub-inhibitory concentrations. Morphological changes of the MRSA cells exposed to Ag3PO4 powder were investigated by the FE-SEM analysis, and a possible mechanism involving the release of dissolved Ag+, together with the production of reactive photocatalytic oxygen species is proposed based on the experimental results. DOI: http://dx.doi.org/10.17807/orbital.v13i3.156

Increasing the photocatalytic and fungicide activities of Ag3PO4 microcrystals under visible-light irradiation

The present study reports for the first time the performance of silver phosphate (Ag3PO4) microcrystals as photocatalyst (degradation of Rodamine B-RhB) and antifungal agent (against Candida albicans–C. albicans) under visible-light irradiation (455 nm). Ag3PO4 microcrystals were synthesized by a simple co-precipitation (CP) method at room temperature. The structural and electronic properties of the as-synthetized Ag3PO4 have been investigated before and after 4 cycles of RhB degradation under visible light using X-ray diffraction (XRD), micro-Raman spectroscopy, UV–Vis spectrophotometer and field emission scanning electron microscopy (FE-SEM) images. The antifungal activity was analyzed in planktonic cells and 48h-biofilm of C. albicans by colony forming units (CFU) counting, confocal laser and FE-SE microscopies. Statistical analysis was carried out using SPSS software. Morphological and structural modifications of Ag3PO4 were observed upon recycling. After 4 recycles, the material maintained its photodegradation property; an eightfold increase in the efficiency of Ag3PO4 was observed in planktonic cells and a two fold increase in biofilm when irradiated under visible light. Thus, higher antifungal effectiveness against C. albicans was obtained when associated with visible-light irradiation.Funding for open access charge: CRUE-Universitat Jaume

Effect of a Silver Nanoparticles Solution on Staphylococcus aureus

An AgNPs solution was synthesized by chemical reduction, characterized, and tested against Candida glabrata, Candida tropicalis, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus (MRSA). Minimum inhibitory (MICs) and minimum fungicidal/bactericidal concentrations (MFC/MBC) were determined on planktonic cells. Also, total biofilm mass was determined by crystal violet (CV) staining and morphological changes by scanning electron microscope (SEM). MICs for C. glabrata, C. tropicalis, S. aureus, and MRSA were 15.63, 3.91, 1.95, and 1.95 µg/mL, respectively. MFC for C. glabrata was 62.5 µg/mL and for C. tropicalis 15.63 µg/mL The same MBC (3.91 µg/mL) was observed for S. aureus and MRSA. CV assay showed that the AgNPs (1000 μg/mL) promoted reductions in biofilm mass of ~60% for C. glabrata and ~35% for C. tropicalis. A reduction of ~20% in C. tropicalis biomass was also observed at the concentration of 3.91 µg/mL. No significant effect on total biomass was found for S. aureus and MRSA. SEM images revealed that C. glabrata and C. tropicalis biofilm cells, exposed to the AgNPs (1000 μg/mL), had an irregular and shriveled appearance. AgNPs solution exhibited considerable antimicrobial activity against important fungal and bacterial pathogens, associated with several oral and systemic diseases, and has potential as an antimicrobial agent.Rede NanoBioMed/CAPESFAPESP (08/07454-9)PDI/Programa de Internacionalização UNESP/PROPe/Pró-Reitoria de Pós-Graduação da Universidade Estadual Paulista Júlio de Mesquita Filho (PROPG)/FUNDUNES

Selective Synthesis of α-, β-, and γ-Ag2WO4 Polymorphs: Promising Platforms for Photocatalytic and Antibacterial Materials

Silver tungstate (Ag2WO4) shows structural polymorphism with different crystalline phases, namely, orthorhombic, hexagonal, and cubic structures that are commonly known as α, β, and γ, respectively. In this work, these Ag2WO4 polymorphs were selectively and successfully synthesized through a simple precipitation route at ambient temperature. The polymorph-controlled synthesis was conducted by means of the volumetric ratios of the silver nitrate/tungstate sodium dehydrate precursors in solution. The structural and electronic properties of the as-synthesized Ag2WO4 polymorphs were investigated by using a combination of X-ray diffraction and Rietveld refinements, X-ray absorption spectroscopy, X-ray absorption near-edge structure spectroscopy, field-emission scanning electron microscopy images, and photoluminescence. To complement and rationalize the experimental results, first-principles calculations, at the density functional theory level, were carried out, leading to an unprecedented glimpse into the atomic-level properties of the morphology and the exposed surfaces of Ag2WO4 polymorphs. Following the analysis of the local coordination of Ag and W cations (clusters) at each exposed surface of the three polymorphs, the structure–property relationship between the morphology and the photocatalytic and antibacterial activities against amiloride degradation under ultraviolet light irradiation and methicillin-resistant Staphylococcus aureus, respectively, was investigated. A possible mechanism of the photocatalytic and antibacterial activity as well the formation process and growth of the polymorphs is also explored and proposed

Tuning the Morphological, Optical, and Antimicrobial Properties of α-Ag2WO4 Microcrystals Using Different Solvents

New, effective antimicrobial agents are constantly being evaluated for addressing the increased prevalence of bacterial and fungal infections and emerging drug resistance. In this study, α- Ag2WO4 microcrystals were prepared by controlled coprecipitation (90 °C for 10 min) in different solvents (e.g., water, an alcoholic solution, and an ammoniacal solution). From the X-ray diffraction results, the newly synthesized α-Ag2WO4 microcrystals are wellindexed to the orthorhombic structure. Two morphologies were seen by field-emission scanning electron microscopy: microrods in the alcoholic solution and flowerlike structures in water and the ammoniacal solution. The synthesized α-Ag2WO4 microcrystals exhibited antimicrobial activity against Candida albicans, Escherichia coli, and methicillin-resistant Staphylococcus aureus. In addition, the antibacterial performance of the α-Ag2WO4 samples as a function of their structural and morphological features was discussed

Development of Antibiofilm Substances by Endophytic Microorganisms with an Emphasis on Medicine

The growing antimicrobial resistance and persistence of pathogenic microorganisms in infections–particularly in nosocomial infections–have become a major problem for public health worldwide. One of the main causes of these issues is the formation of biofilms, which are microbial communities associated with extracellular polymeric substances (EPS) that form a slimy extracellular matrix, causing the bacteria to become more tolerant to usual drugs in these structures. Thus, the search for new antibiofilm compounds is part of a strategy to deal with this problem. Endophytic microorganisms such as bacteria and fungi, mutualistically associated with plants, are sources of compounds with biological properties, including antimicrobials, and can be important allies in the synthesis of antibiofilm. These secondary metabolites can interfere with cell-to-cell communication and cell adhesion ability, promoting the dispersal of bacterial colonies and affecting biofilm. Since endophytes are cultivable in laboratory conditions, these microorganisms are environmentally friendly, as they do not contribute to pollution, are easy to handle and are produced on a large scale. Furthermore, metabolites from endophytes are of natural origin and may contribute to the reduced use of synthetic drugs. Considering these aspects, this chapter will focus on the characterization of endophytic microorganisms as potential active sources of antibiofilm and antimicrobial compounds with applications in medicine

Unvealing the role of β-Ag2MoO4 microcrystals to the improvement of antibacterial activity

Crystal morphology with different surfaces is important for improving the antibacterial activity of materials. In this experimental and theoretical study, the antibacterial activity of β-Ag2MoO4 microcrystals against the Gram-positive bacteria, namely, methicillin-resistant Staphylococcus aureus (MRSA), and the Gram-negative bacteria, namely, Escherichia coli (E. coli), was investigated. In this study, β-Ag2MoO4 crystals with different morphologies were synthetized by a simple co-precipitation method using three different solvents. The antimicrobial efficacy of the obtained microcrystals against both bacteria increased according to the solvent used in the following order: water < ammonia < ethanol. Supported by experimental evidence, a correlation between morphology, surface energy, and antibacterial performance was established. By using the theoretical Wulff construction, which was obtained by means of density functional calculations, the morphologies with large exposition of the (001) surface exhibited superior antibacterial activity. This study provides a low cost route for synthesizing β-Ag2MoO4 crystals and a guideline for enhancing the biological effect of biocides on pathogenic bacteria by the morphological modulation

Electron beam irradiation for the formation of thick Ag film on Ag3PO4

This study demonstrates that the electron beam irradiation of materials, typically used in characterizationmeasurements, could be employed for advanced fabrication, modification, and functionalization ofcomposites. We developed irradiation equipment using an electron beam irradiation source to beapplied in materials modification. Using this equipment, the formation of a thick Agfilm on the Ag3PO4semiconductor is carried out by electron beam irradiation for thefirst time. This is confirmed by variousexperimental techniques (X-ray diffraction,field-emission scanning electron microscopy, Ramanspectroscopy, and X-ray photoelectron spectroscopy) andab initiomolecular dynamics simulations. Ourcalculations demonstrate that, at the earlier stages, metallic Ag growth is initiated preferentially at the(110) surface, with the reduction of surface Ag cations forming metallic Ag clusters. As the (100) and (111)surfaces have smaller numbers of exposed Ag cations, the reductions on these surfaces are slower andare accompanied by the formation of O2molecules