Green Synthesis of Silver Nano-particles by Macrococcus bovicus and Its Immobilization onto Montmorillonite Clay for Antimicrobial Functionality

Spectral and conductivity measurements insights on loading mechanisms of DMSO/water-kaolin complexes

Kaolin, a naturally occurring clay mineral renowned for its distinctive properties, holds significant importance across various industries. The integration of dimethyl sulfoxide (DMSO) into kaolin matrices, both in the presence and absence of water, has been extensively explored for its potential to enhance material characteristics. Addressing debates surrounding the proposed adsorption mechanism for the type I structure of DMSO, this study undertook a comprehensive physicochemical characterization of DMSO-kaolin complexes (DMSO-KCs) derived from untreated (UnK) and HCl-treated (HK) Egyptian ore, with a focus on elucidating the loading mechanism facilitated by water. Key insights gleaned from electrical conductivity, dielectric constant, and Fine Testing Technology - Fourier-transform infrared (FTT-FTIR) measurements, shedding light on the bonding nature of DMSO-KCs. FTT-FTIR analysis revealed two stages of water departure at 180 °C, with the final stage coinciding with the release of pyrolysis gases, confirming the catalytic degradation of DMSO. Through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), two distinct bonding types of DMSO molecules with kaolinite were identified: amorphous adsorbed (type I) and lattice-oriented intercalated (type II). Electrical characteristic evaluations within the temperature range of room temperature (RT) to 260 °C and frequency range of 42 Hz-1 MHz revealed that DMSO intercalation enhances the electrical properties of kaolin. Hydrated DMSO-KCs exhibited higher values of σac and ɛ' compared to non-hydrated samples. The activation energy (Ea) values for HCl-treated samples were smaller than those of untreated ones. Alternating current (AC) conductivity analysis indicated predominantly ionic behavior with frequency and temperature dependency in both HCl-treated and untreated kaolin. Our findings substantiate the adsorption mechanism of Type I DMSO, highlighting its amorphous nature, instability, and catalytic degradation over time, in contrast to the intercalated type II. This elucidation is pivotal for understanding the behavior of DMSO-KCs across diverse applications, including electronics, ceramics, and materialsscience.

A review of microbes mediated biosynthesis of silver nanoparticles and their enhanced antimicrobial activities

In recent decades, biosynthesis of metal and (or) metal oxide nanoparticles using microbes is accepted as one of the most sustainable, cost-effective, robust, and green processes as it does not encompass the usage of largely hazardous chemicals. Accordingly, numerous simple, inexpensive, and environmentally friendly approaches for the biosynthesis of silver nanoparticles (AgNPs) were reported using microbes avoiding conventional (chemical) methods. This comprehensive review detailed an advance made in recent years in the microbes-mediated biosynthesis of AgNPs and evaluation of their antimicrobial activities covering the literature from 2015-till date. It also aimed at elaborating the possible effect of the different phytochemicals, their concentrations, extraction temperature, extraction solvent, pH, reaction time, reaction temperature, and concentration of precursor on the shape, size, and stability of the synthesized AgNPs. In addition, while trying to understand the antimicrobial activities against targeted pathogenic microbes the probable mechanism of the interaction of produced AgNPs with the cell wall of targeted microbes that led to the cell's reputed and death have also been detailed. Lastly, this review detailed the shape and size-dependent antimicrobial activities of the microbes-mediated AgNPs and their enhanced antimicrobial activities by synergetic interaction with known commercially available antibiotic drugs.

Quercetin- and caffeic acid-functionalized chitosan-capped colloidal silver nanoparticles: one-pot synthesis, characterization, and anticancer and antibacterial activities

The presented study comprises the one-pot synthesis and the characterization of quercetin- and caffeic acid-functionalized chitosan-capped colloidal silver nanoparticles (Ch/Q- and Ch/CA-Ag NPs), and their antibacterial and anticancer activities. The formation of Ch/Q- and Ch/CA-Ag NPs has been confirmed by ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The characteristic surface plasmon resonance (SPR) absorption band has been found at 417 and 424 nm for Ch/Q- and Ch/CA-Ag NPs, respectively. The formation of a chitosan shell comprising quercetin and caffeic acid, which surround the colloidal core Ag NPs, was confirmed by UV-vis, and FTIR analyses, and monitored by TEM microscopy. The size of nanoparticles has been determined as 11.2 and 10.3 nm for Ch/Q- and Ch/CA-Ag, respectively. The anticancer activity of Ch/Q- and Ch/CA-Ag NPs has been evaluated against U-118 MG (human glioblastoma) and ARPE-19 (human retinal pigment epithelium) cells. Both NPs showed anticancer activity, but Ch/Q-Ag NPs seemed to be more effective on cancer cell lines (U-118 MG) in comparison to healthy ones (ARPE-19). Furthermore, the antibacterial activity of Ch/Q- and Ch/CA-Ag NPs against Gram-negative (P. aeruginosa and E. coli) and Gram-positive (S. aureus and S. epidermidis) bacteria was determined, and dose-dependent antibacterial effects were found.

A Review on Montmorillonite-Based Nanoantimicrobials: State of the Art

One of the crucial challenges of our time is to effectively use metal and metal oxide nanoparticles (NPs) as an alternative way to combat drug-resistant infections. Metal and metal oxide NPs such as Ag, Ag₂O, Cu, Cu₂O, CuO, and ZnO have found their way against antimicrobial resistance. However, they also suffer from several limitations ranging from toxicity issues to resistance mechanisms by complex structures of bacterial communities, so-called biofilms. In this regard, scientists are urgently looking for convenient approaches to develop heterostructure synergistic nanocomposites which could overcome toxicity issues, enhance antimicrobial activity, improve thermal and mechanical stability, and increase shelf life. These nanocomposites provide a controlled release of bioactive substances into the surrounding medium, are cost effective, reproducible, and scalable for real life applications such as food additives, nanoantimicrobial coating in food technology, food preservation, optical limiters, the bio medical field, and wastewater treatment application. Naturally abundant and non-toxic Montmorillonite (MMT) is a novel support to accommodate NPs, due to its negative surface charge and control release of NPs and ions. At the time of this review, around 250 articles have been published focusing on the incorporation of Ag-, Cu-, and ZnO-based NPs into MMT support and thus furthering their introduction into polymer matrix composites dominantly used for antimicrobial application. Therefore, it is highly relevant to report a comprehensive review of Ag-, Cu-, and ZnO-modified MMT. This review provides a comprehensive overview of MMT-based nanoantimicrobials, particularly dealing with preparation methods, materials characterization, and mechanisms of action, antimicrobial activity on different bacterial strains, real life applications, and environmental and toxicity issues.

Genotoxicity and Toxicity Assessment of a Formulation Containing Silver Nanoparticles and Kaolin: An In Vivo Integrative Approach

A new material composed of a kaolin base with silver nanoparticles (AgNPs) attached to its surface was developed, as an alternative to antibiotics used as supplements in animal feed. As part of its safety assessment, an in vivo geno-toxicological evaluation of this material was conducted in rats. First, a preliminary dose finding study was carried out to decide the doses to be tested in the main study: 50, 300 and 2000 mg/kg b.w. For the main study, a combined strategy composed of the MN test (TG 474) and the comet assay (TG 489), integrated in a repeated dose 28-day oral toxicity study (TG 407), was performed. A No Observed Adverse Effect Level (NOAEL) of 2000 mg of the silver-kaolin formulation/kg b.w. by oral route, for 28 days, was determined. The silver-kaolin formulation did not induce micronuclei in bone marrow, or DNA strand breaks (SBs) or alkali labile sites (ALS) in liver, spleen, kidney or duodenum at any dose. The modified Fpg comet assay did not reveal oxidized bases in the same tissues at the dose of 2000 mg/kg b.w. Silver was quantified by ICP-MS in all the target organs, confirming the negative results obtained under these conditions.

Bacillales: From Taxonomy to Biotechnological and Industrial Perspectives

For a long time, the genus Bacillus has been known and considered among the most applicable genera in several fields. Recent taxonomical developments resulted in the identification of more species in Bacillus-related genera, particularly in the order Bacillales (earlier heterotypic synonym: Caryophanales), with potential application for biotechnological and industrial purposes such as biofuels, bioactive agents, biopolymers, and enzymes. Therefore, a thorough understanding of the taxonomy, growth requirements and physiology, genomics, and metabolic pathways in the highly diverse bacterial order, Bacillales, will facilitate a more robust designing and sustainable production of strain lines relevant to a circular economy. This paper is focused principally on less-known genera and their potential in the order Bacillales for promising applications in the industry and addresses the taxonomical complexities of this order. Moreover, it emphasizes the biotechnological usage of some engineered strains of the order Bacillales. The elucidation of novel taxa, their metabolic pathways, and growth conditions would make it possible to drive industrial processes toward an upgraded functionality based on the microbial nature.

Silica-Gel Incorporated Biosynthesized-Silver Nanoparticles for Sustainable Antimicrobial Treatment of Brackish Water Aquaculture

Treatment of brackish water from pathogenic microbes is crucial for sustainable aquaculture production and preventing the spread of infectious diseases. However, the treatment of brackish water is still challenging due to the high salinity and the high antimicrobial resistance. Here, we exploit a facile and effective approach to synthesize silica gel embedded with silver nanoparticles (7–48 nm) for broad-spectrum antimicrobial activity. The incorporation of silver nanoparticles into silica gel (AgNPs@SG) is confirmed by flame atomic absorption spectrometry, X-ray diffraction, N2 physisorption, and transmission electron microscopy. The AgNPs@SG material exhibits wide-spectrum antimicrobial activity against the studied microorganisms (Pseudomonas aeruginosa, Escherichia coli, and Candida albicans) due to preventing the aggregation of silver nanoparticles and their effective contact with the microorganisms. Most importantly, the applicability of the synthesized AgNPs@SG for the microbial treatment of brackish water is investigated on different water samples collected from Manzala Lake. Remarkably, the amount of viable bacteria in the brackish water decreases by about 93% using AgNPs@SG material that not only combats antibiotic-resistant strains but also works under harsh conditions such as multiple-source contamination, high eutrophic state, and salinity.

In Vitro Genotoxicity Evaluation of an Antiseptic Formulation Containing Kaolin and Silver Nanoparticles

Worldwide antimicrobial resistance is partly caused by the overuse of antibiotics as growth promoters. Based on the known bactericidal effect of silver, a new material containing silver in a clay base was developed to be used as feed additive. An in vitro genotoxicity evaluation of this silver-kaolin clay formulation was conducted, which included the mouse lymphoma assay in L5178Y TK+/− cells and the micronucleus test in TK6 cells, following the principles of the OECD guidelines 490 and 487, respectively. As a complement, the standard and Fpg-modified comet assays for the evaluation of strand breaks, alkali labile sites and oxidative DNA damage were also performed in TK6 cells. The formulation was tested without metabolic activation after an exposure of 3 h and 24 h; its corresponding release in medium, after the continuous agitation of the silver-kaolin for 24 h was also evaluated. Under the conditions tested, the test compound did not produce gene mutations, chromosomal aberrations or DNA damage (i.e., strand breaks, alkali labile sites or oxidized bases). Considering the results obtained in the present study, the formulation seems to be a promising material to be used as antimicrobial in animal feed.

Modified montmorillonite-bacterial cellulose composites as a novel dressing system for pressure injury

The main objective of this study was to investigate the effects of bacterial cellulose hydrogel (BCH) incorporated into montmorillonite (MMT) and its underlying mechanisms of action on a skin wound healing mouse model following pressure injury model. Komagataeibacter hansenii was used to obtain 5 cm in diameter and 0.8 mm of thickness circular bacterial cellulose (BC) sheets, which were incorporated with MMT by deposition ex-site using a 0.1% MMT suspension (100 rpm for 24 h at 28 °C). Afterward, Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) were used to characterize the bacterial cellulose hydrogel incorporated into montmorillonite (BCH-MMT). The pressure injury model was assessed by macroscopic and histological analysis in male Swiss mice. Both, BC and BCH-MMT, showed a typical FTIR spectrum of cellulosic substrates with pronounces bands around 3344, 2920, 1637, and 1041 cm-1 while microparticles of MMT dispersed uniformly throughout BC were revealed by SEM photographs. Animals treated with BCH-MMT showed significant healing of pressure ulcers as demonstrated by reduced area of redness and spontaneous hyperalgesia, lower amounts of in-site inflammatory cells (to the same level as the positive control Dersani®) and ultimately, complete epidermis re-epithelialization and tissue regeneration. Altogether, these findings suggest that a modified BCH-MMT film could serve as scaffolding for skin tissue engineering and potentially as a novel dressing material for pressure injury.

Incorporation of silver nanoparticles into active antimicrobial nanocomposites: Release behavior, analyzing techniques, applications and safety issues

Employing new strategies to develop novel composite systems has become a popular area of interest among researchers. Raising people's awareness and their attention to the health and safety issues are key parameters to achieve this purpose. One of the recommended strategies is the utilization of nanoparticles within the matrix of composite materials to improve their physical, mechanical, structural and antimicrobial characteristics. Silver nanoparticles (Ag NPs) have attracted much attention for nanocomposite applications mainly due to their antimicrobial characteristics. Herein, the current review will focus on the different methods for preparing antimicrobial nanocomposites loaded with Ag NPs, the release of Ag NPs from these nanostructures in different media, analyzing techniques for the evaluation of Ag release from nanocomposites, potential applications, and safety issues of nanocomposites containing Ag NPs. The applications of Ag NPs-loaded nanocomposites have been extensively established in food, biomedical, textile, environmental and pharmacological areas mainly due to their antibacterial attributes. Several precautions should be addressed before implementation of Ag NPs in nanocomposites due to the health and safety issues.

Application of Bacillus sp. protease in the fabrication of silver/silver chloride nanoparticles in solution and cotton gauze bandages

Silver (Ag)/silver chloride (AgCl) nanoparticles have been used worldwide for their antimicrobial activity. Proteases play an important role in many physiological processes during wound healing. Therefore, the aim of this study was to fabricate silver-type nanoparticles exhibiting protease activity for medical applications such as wound healing and dressings. The Ag/AgCl nanoparticles were fabricated using Bacillus sp. protease and visible light activation. The size of the fabricated nanoparticles was estimated to be 35.29 ± 6.43 nm. The nanoparticles were coated on a cotton gauze bandage using immersion and ultrasonication. Scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed that the nanoparticles could be used to coat the gauze bandage. Synchrotron radiation X-ray tomographic microscopy indicated that coating with the nanoparticles did not destroy the packing of cotton fibers in the gauze bandage. The nanoparticles exhibited fibrinolytic and collagenolytic activities. Protease activity remained after the nanoparticle coating was applied to the gauze bandage. The nanoparticles were not absorbed on a gelatin agar plate after incubation at 37 °C for 18 H. These results suggest that the coated cotton gauze bandage may be safe for further use, and the nanoparticles may not be absorbed into animal or human skin.

Encapsulation of Biosynthesized Nanosilver in Silica Composites for Sustainable Antimicrobial Functionality

Silver nanoparticles (AgNPs) have become known as a broad-spectrum antimicrobial agent. The antimicrobial activity of AgNPs is dependent on the particle size and the dispersion status. In this study, a simple and effective approach is developed for sequestering the biosynthesized AgNPs in silica composites during the gel formation of MCM-41. Composites with different Ag concentrations of 0.034% (Ag1@MCM-41), 0.151% (Ag2@MCM-41), and 0.369% (Ag3@MCM-41) are synthesized and then heated at 400 °C to produce Ag1@MCM-41H, Ag2@MCM-41H, and Ag3@MCM-41H, respectively. The samples are characterized by flame atomic absorption spectrometry, Fourier-transform infrared spectroscopy, X-ray diffraction, N2 physisorption, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The AgNPs are confirmed to be highly dispersed in the amorphous silica framework. The antimicrobial activity of the AgNP-silica samples is investigated against Staphylococcus aureus, Escherichia coli, and Candida albicans using the cup-plate and the plate-count techniques. The results show an excellent antimicrobial effect of these samples against the studied microorganisms. Importantly, the AgNP-silica samples are found to be stable up to 58 months under ambient conditions. These stable and powerful antimicrobial composites provide a more practical and effective strategy for combating biomedical pathogens and public health threats.

Safety and efficacy of PLGA(Ag-Fe3O4)-coated dental implants in inhibiting bacteria adherence and osteogenic inducement under a magnetic field

Introduction

The placement of dental implants is performed in a contaminated surgical field in the oral cavity, which may lead to implant failure. Bacterial adhesion and proliferation (Streptococcus mutans, Porphyromonas gingivalis) often lead to implant infections. Although Ag nanoparticles hold great promise for a broad spectrum of antibacterial activities, their runoff from dental implants compromises their antibacterial efficacy and potentially impairs osteoblast proliferation. Thus, this aspect remains a primary challenge and should be controlled.

Materials and methods

In this study, PLGA(Ag-Fe₃O₄) was modified on the implanted tooth surface and was characterized by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The magnetic and antibacterial properties were also determined.

Results

Results showed that Ag successfully bonded with Fe₃O₄, and Ag-Fe₃O₄ not only exerted superparamagnetism but also exhibited antibacterial activity almost identical to silver nanoparticles (nano-Ag). The PLGA(Ag-Fe₃O₄) coating could significantly maintain the antibacterial activity and avoid bacterial adhesion to the implant. Compared with the blank control group, PLGA(Ag-Fe₃O₄) under magnetic field-coated samples had a significantly lower amount of colonized S. mutans (P<0.01). Osteoblast proliferation results showed that the coated samples did not exhibit cytotoxicity and could promote osteoblast proliferation as shown by MTT, alkaline phosphatase, and the nucleolar organizer region count.

Conclusion

We developed a novel Ag biologically compatible nanoparticle in this study without compromising the nano-Ag antibacterial activity, which provided continuous antibacterial action.

The Genus Macrococcus: An Insight Into Its Biology, Evolution, and Relationship With Staphylococcus

The Gram-positive genus Macrococcus is composed of eight species that are evolutionarily closely related to species of the Staphylococcus genus. In contrast to Staphylococcus species, species of Macrococcus are generally regarded to be avirulent in their animal hosts. Recent reports on Macrococcus have focused on the presence of novel methicillin resistance genes in Macrococcus caseolyticus and Macrococcus canis, with the discovery of the first plasmid-encoded methicillin resistance gene in clinical Staphylococcus aureus of probable macrococcal origin generating further interest in these organisms. Furthermore, M. caseolyticus has been associated with flavor development in certain fermented foods and its potential as a food bio-preservative has been documented. The potential application of these organisms in food seems at odds with the emerging information regarding antibiotic resistance and is prompting further examination of the potential safety issues associated with such strains, given the European Food Safety Authority framework for the safety evaluation of microorganisms in the food chain. A comprehensive understanding of the genus would also contribute to understanding the evolution of staphylococci in terms of its acquisition of antibiotic resistance and pathogenic potential. In this review, we discuss the current knowledge on Macrococcus with regard to their phenotypic capabilities, genetic diversity, and evolutionary history with Staphylococcus. Comparative genomics of the sequenced Macrococcus species will be discussed, providing insight into their unique metabolic features and the genetic structures carrying methicillin resistance. An in-depth understanding of these antibiotic resistance determinants can open the possibilities for devising better preventative strategies for an unpredictable future.

Antimicrobial cellulosic hydrogel from olive oil industrial residue

The cellulose-based antimicrobial hydrogel was prepared from seed and husk cellulosic fibers of olive industry residues by load silver nanoparticles (AgNPs) onto grafted acrylamide monomer (Am) cellulosic fibers. The grafting approach was the free radical mechanism by utilizing ceric ammonium nitrate (CAN) as initiator in aqueous medium and N,N methylene bisacrylamide (MBAm) as a cross linker. The effect of different grafting conditions on the properties of produced hydrogels has been studied by determining the grafting parameters, i.e. concentration of Am, MBAm, grafting time and temperature to optimize grafting yield (G %), grafting efficiency (GE %), and swelling %. Characterizations of the obtained hydrogels were performed through monitoring swelling behavior, FTIR spectroscopy, SEM, and EDX. AgNPs were grown into the prepared hydrogel. Hydrogel/AgNPs were characterized by FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The hydrogel loaded AgNPs exhibit high efficient antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans.

Extracorporeal magnetic approach to reduce the unwanted side-effects and improve antibacterial activity of Ag/Fe3 O4 nanocomposites in rat

While Ag nanoparticles hold great promise for broad spectrum antibacterial activity, the potential risks of Ag nanoparticles (NPs) on human health remain a challenge. In this study, Ag/Fe₃ O₄ composites have been successfully prepared and characterized by transmission electron microscopy, X-ray powder diffraction, and Fourier-transform infrared spectroscopy, and their magnetic and antibacterial properties have been assessed. In vivo results show that the antibacterial effect of 500 μg/mL Ag/Fe₃ O₄ nanocomposites was significantly higher than that of 1000 μg/mL AgNPs after 72 h of treatment (p < 0.01). Hematoxylin and eosin (HE) staining showed that squamous epithelium and dermis collagen fibers formed in the Ag/Fe₃ O₄ group after 8 days treatment. Wound closure was significantly better for the Ag/Fe₃ O₄ group than for the AgNPs group. On the other hand, there was less Ag in blood, liver, and kidney in the Ag/Fe₃ O₄ group, as more Ag was retained in the wound. According to lactate dehydrogenase, γ-glutamyl transpeptidase, and reactive oxygen species results, Ag/Fe₃ O₄ nanocomposites caused less unwanted side-effects. This work presents a new paradigm to reduce the unwanted side-effects of AgNPs and improve their antibacterial activity, providing a new avenue for wound healing. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2029-2036, 2018.