Adsorptive property of Cu2+–ZnO/cetylpyridinium–montmorillonite complexes for pathogenic bacterium in vitro

A mica filter enables bacterial enrichment from large volumes of natural water for sensitive monitoring of pathogens by nanopore sequencing

Nanopore sequencing is extremely promising for the high-throughput detection of pathogenic bacteria in natural water; these bacteria may be transmitted to humans and cause waterborne infectious diseases. However, the concentration of pathogenic bacteria in natural water is too low to be detected directly by nanopore sequencing. Herein, we developed a mica filter to enrich over 85% of bacteria from > 10 L of natural water in 100 min, which led to a 102-fold improvement in the assay limits of the MinION sequencer for assessing pathogenic bacteria. Correspondingly, the sequencing time of S. Typhi detection at a concentration as low as 105 CFU/L was reduced from traditional 48 h to 3 h. The bacterial adsorption followed pseudo-first-order kinetics and the successful adsorption of bacteria to the mica filter was confirmed by scanning electron microscopy and Fourier infrared spectroscopy et al. The mica filter remained applicable to a range of water samples whose quality parameters were within the EPA standard limits for freshwater water. The mica filter is thus an effective tool for the sensitive and rapid monitoring of pathogenic bacteria by nanopore sequencing, which can provide timely alerts for waterborne transmission events.

AIEgen-Based Nanomaterials for Bacterial Imaging and Antimicrobial Applications: Recent Advances and Perspectives

Microbial infections have always been a thorny problem. Multi-drug resistant (MDR) bacterial infections rendered the antibiotics commonly used in clinical treatment helpless. Nanomaterials based on aggregation-induced emission luminogens (AIEgens) recently made great progress in the fight against microbial infections. As a family of photosensitive antimicrobial materials, AIEgens enable the fluorescent tracing of microorganisms and the production of reactive oxygen (ROS) and/or heat upon light irradiation for photodynamic and photothermal treatments targeting microorganisms. The novel nanomaterials constructed by combining polymers, antibiotics, metal complexes, peptides, and other materials retain the excellent antimicrobial properties of AIEgens while giving other materials excellent properties, further enhancing the antimicrobial effect of the material. This paper reviews the research progress of AIEgen-based nanomaterials in the field of antimicrobial activity, focusing on the materials' preparation and their related antimicrobial strategies. Finally, it concludes with an outlook on some of the problems and challenges still facing the field.

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.

AIEgen Intercalated Nanoclay-Based Photodynamic/Chemodynamic Theranostic Platform for Ultra-Efficient Bacterial Eradication and Fast Wound Healing

With the emergence and global spread of bacterial resistance, pathogenic bacterial infections have become a serious threat to human health. Thus, therapeutic strategies with highly antibacterial efficacy and a low tendency to induce drug resistance are strongly desired to combat bacterial infections. Here, an ultra-efficient photodynamic/chemodynamic theranostics platform is developed by intercalating an aggregation-induced emission (AIE) photosensitizer, TPCI, into the nanolayers of iron-bearing montmorillonite (MMT). The formed TPCI/MMT composite can not only perform efficient photodynamic therapy (PDT) through a burst generation of singlet oxygen (¹O₂) upon white light illumination but also continuously implement chemodynamic therapy (CDT) by converting endogenous hydrogen peroxide into highly toxic hydroxyl radicals (^•OH) due to iron release. In addition, the fluorescence of TPCI/MMT can be activated due to the AIE feature of TPCI, which helps guide the location of the antimicrobials. The combination of such powerful bombs (PDT) and unremitting ambushes (CDT) in TPCI/MMT can synergistically and effectively eliminate bacteria and promote faster wound healing in vivo with good biocompatibility and low side effects. The smart and simple design of TPCI/MMT provides a representative paradigm for achieving efficient antimicrobials to combat the coming resistance crisis.

On the mechanism behind enhanced antibacterial activity of alkyl gallate esters against foodborne pathogens and its application in Chinese icefish preservation

The objective of this study was to investigate antibacterial activities and action mode of alkyl gallates against three food-related bacteria. Results show that the length of the alkyl chain plays a critical role in eliciting their antibacterial activities and octyl gallate (GAC8) exhibited an outstanding bactericidal effect against these strains. A possible bactericidal mechanism of GAC8 against E. coli was fully elucidated by analyzing associated changes in cellular functions of E. coli, including assessments of membrane modification and intracellular oxidation state. Our data strongly suggested that GAC8 functions outside and inside the bacterial membrane and causes increased intracellular reactive oxygen species (hydroxyl radicals) and subsequent oxidative damage. We demonstrated that the hydroxyl radical formation induced by GAC8 is the end product of an oxidative damage cellular death pathway involving a transient depletion of NADH, the tricarboxylic acid cycle, intrinsic redox cycling activities, and stimulation of the Fenton reaction. Also, chitosan-based edible films containing GAC8 have unique superiorities for icefish preservation at 4 °C. This research highlights the effectiveness of GAC8 as an attractive antibacterial, which possesses both antioxidant and antibacterial activities and can be used as a multifunctional food additive combined with the benefit of active packaging for food preservations.

Bimetallic Nanoparticles for Antimicrobial Applications

Highly effective antimicrobial agents are needed to control the emergence of new bacterial strains, their increased proliferation capability, and antibacterial resistance that severely impact public health, and several industries including water, food, textiles, and oil and gas. Recently, bimetallic nanoparticles, formed via integration of two different metals, have appeared particularly promising with antibacterial efficiencies surpassing that of monometallic counterparts due to synergistic effects, broad range of physiochemical properties, and diverse mechanisms of action. This work aims to provide a review on developed bimetallic and supported bimetallic systems emphasizing in particular on the relation between synthesis routes, properties, and resulting efficiency. Bimetallic nanostructures on graphene, zeolites, clays, fibers, polymers, as well as non-supported bimetallic nanoparticles are reviewed, their synthesis methods and resulting properties are illustrated, along with their antimicrobial activity and potential against different strains of microbes.

Adhesion of bacteria to pyrophyllite clay in aqueous solution

The aim of this study was to investigate the adhesion of bacteria (Escherichia coli) to pyrophyllite clay using batch and flow-through column experiments. Batch results demonstrated that pyrophyllite was effective in removing bacteria (94.5 +/- 2.0%) from aqueous solution (1 mM NaCl solution; pyrophyllite dose of 1 g/ml). At solution pH 7.1, negatively-charged bacteria could be removed due to their adhesion to positively-charged surfaces of pyrophyllite (point of zero charge = 9.2). Column results showed that pyrophyllite (per cent removal of 94.1 +/- 2.3%) was far more effective in bacterial adhesion than quartz sand (53.6 +/- 5.3%) under the given experimental conditions (flow rate of 0.3 ml/min; solution of 1 mM NaCl + 0.1 mM NaHCO3). Bacterial removal in pyrophyllite columns increased from 90 to 100% with decreasing flow rate from 0.6 to 0.15 ml/min due to increasing contact time between bacteria and filter materials. In addition, bacterial removal remained relatively constant at 94-97% even though NaHCO3 concentration increased from 0.1 to 10 mM (flow rate of 0.3 ml/min). This could be related to the fact that pyrophyllite remained positively-charged even though the solution conditions changed. This study demonstrates that pyrophyllite could be used as adsorptive filter materials in the removal of bacteria.