Mechanisms of bacterial resistance to environmental silver and antimicrobial strategies for silver: A review

The good antimicrobial properties of silver make it widely used in food, medicine, and environmental applications. However, the release and accumulation of silver-based antimicrobial agents in the environment is increasing with the extensive use of silver-based antimicrobials, and the prevalence of silver-resistant bacteria is increasing. To prevent the emergence of superbugs, it is necessary to exercise rational and strict control over drug use. The mechanism of bacterial resistance to silver has not been fully elucidated, and this article provides a review of the progress of research on the mechanism of bacterial resistance to silver. The results indicate that bacterial resistance to silver can occur through inducing silver particles aggregation and Ag+ reduction, inhibiting silver contact with and entry into cells, efflux of silver particles and Ag+ in cells, and activation of damage repair mechanisms. We propose that the bacterial mechanism of silver resistance involves a combination of interrelated systems. Finally, we discuss how this information can be used to develop the next generation of silver-based antimicrobials and antimicrobial therapies. And some antimicrobial strategies are proposed such as the "Trojan Horse" - camouflage, using efflux pump inhibitors to reduce silver efflux, working with "minesweeper", immobilization of silver particles.

A novel approach to wound healing: Green synthetic nano-zinc oxide embedded with sodium alginate and polyvinyl alcohol hydrogels for dressings

Wound healing constitutes a formidable challenge within the healthcare system, attributable to infection risks and protracted recovery periods. The pressing need for innovative wound healing methods has spurred the urgency to develop novel approaches. This study sought to advance wound healing by introducing a novel approach employing a composite sponge dressing. The composite sponge dressing, derived from LFL-ZnO (synthesized through the green methodology utilizing Lactobacillus plantarum ZDY2013 fermentation liquid), polyvinyl alcohol (PVA), and sodium alginate (SA) via a freeze-thaw cycle and freeze-drying molding process, demonstrated notable properties. The findings elucidate the commendable swelling, moisturizing, and mechanical attributes of the SA/LFL-ZnO/PVA composite sponge dressing, characterized by a porous structure. Remarkably, the dressing incorporating LFL-ZnO exhibited substantial inhibition against both methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus (S. aureus). Hemolysis and cytotoxicity tests corroborated the excellent biocompatibility of the sponge dressing. In vivo evaluation of the therapeutic efficacy of the 1 mg/mL LFL-ZnO composite dressing on scald wounds and S. aureus-infected wounds revealed its capacity to accelerate wound healing and exert pronounced antibacterial effects. Consequently, the composite sponge dressings synthesized in this study hold significant potential for application in wound treatment.

ZnO based 0-3D diverse nano-architectures, films and coatings for biomedical applications

Thin-film nano-architecting is a promising approach that controls the properties of nanoscale surfaces to increase their interdisciplinary applications in a variety of fields. In this context, zinc oxide (ZnO)-based various nano-architectures (0-3D) such as quantum dots, nanorods/nanotubes, nanothin films, tetrapods, nanoflowers, hollow structures, etc. have been extensively researched by the scientific community in the past decade. Owing to its unique surface charge transport properties, optoelectronic properties and reported biomedical applications, ZnO has been considered as one of the most important futuristic bio-nanomaterials. This review is focused on the design/synthesis and engineering of 0-3D nano-architecture ZnO-based thin films and coatings with tunable characteristics for multifunctional biomedical applications. Although ZnO has been extensively researched, ZnO thin films composed of 0-3D nanoarchitectures with promising thin film device bio-nanotechnology applications have rarely been reviewed. The current review focuses on important details about the technologies used to make ZnO-based thin films, as well as the customization of properties related to bioactivities, characterization, and device fabrication for modern biomedical uses that are relevant. It features biosensing, tissue engineering/wound healing, antibacterial, antiviral, and anticancer activity, as well as biomedical diagnosis and therapy with an emphasis on a better understanding of the mechanisms of action. Eventually, key issues, experimental parameters and factors, open challenges, etc. in thin film device fabrications and applications, and future prospects will be discussed, followed by a summary and conclusion.

Effects of polyamines and indole on the expression of ribosome hibernation factors in Escherichia coli at the translational level

Polyamines and indole are small regulatory molecules that are involved in the adaptation to stress in bacteria, including the regulation of gene expression. Genes, the translation of which is under the regulatory effects of polyamines, form the polyamine modulon. Previously, we showed that polyamines upregulated the transcription of genes encoding the ribosome hibernation factors RMF, RaiA, SRA, EttA and RsfS in Escherichia coli. At the same time, indole affected the expression at the transcriptional level of only the raiA and rmf genes. Ribosome hibernation factors reversibly inhibit translation under stress conditions, including exposure to antibiotics, to avoid resource waste and to conserve ribosomes for a quick restoration of their functions when favorable conditions occur. In this work, we have studied the influence of indole on the expression of the raiA and rmf genes at the translational level and regulatory effects of the polyamines putrescine, cadaverine and spermidine on the translation of the rmf, raiA, sra, ettA and rsfS genes. We have analyzed the mRNA primary structures of the studied genes and the predicted mRNA secondary structures obtained by using the RNAfold program for the availability of polyamine modulon features. We have found that all of the studied genes contain specific features typical of the polyamine modulon. Furthermore, to investigate the influence of polyamines and indole on the translation of the studied genes, we have constructed the translational reporter lacZ-fusions by using the pRS552/λRS45 system. According to the results obtained, polyamines upregulated the expression of the rmf, raiA and sra genes, the highest expression of which was observed at the stationary phase, but did not affect the translation of the ettA and rsfS genes, the highest expression of which took place during the exponential phase. The stimulatory effects were polyamine-specific and observed at the stationary phase, when bacteria are under multiple stresses. In addition, the data obtained demonstrated that indole significantly inhibited translation of the raiA and rmf genes, despite the stimulatory effect on their transcrip- tion. This can suggest the activity of a posttranscriptional regulatory mechanism of indole on gene expression.

Survival of Escherichia coli after high-antibiotic stress is dependent on both the pregrown physiological state and incubation conditions

Introduction

The survival of bacterial cells exposed to antibiotics depends on the mode of action, the antibiotics concentration, and the duration of treatment. However, it also depends on the physiological state of the cells and the environmental conditions. In addition, bacterial cultures contain sub-populations that can survive high antibiotic concentrations, so-called persisters. Research on persisters is challenging due to multiple mechanisms for their formation and low fractions, down to and below one millionth of the total cell population. Here, we present an improved version of the persister assay used to enumerate the amount of persisters in a cell population.

Methods

The persister assay with high antibiotic stress exposure was performed at both growth supporting and non-supporting conditions. Escherichia coli cells were pregrown to various growth stages in shake flasks and bench-top bioreactors. In addition, the physiological state of E. coli before antibiotic treatment was determined by quantitative mass spectrometry-based metabolite profiling.

Results

Survival of E. coli strongly depended on whether the persister assay medium supported growth or not. The results were also highly dependent on the type of antibiotic and pregrown physiological state of the cells. Therefore, applying the same conditions is critical for consistent and comparable results. No direct connection was observed between antibiotic efficacy to the metabolic state. This also includes the energetic state (i.e., the intracellular concentration of ATP and the adenylate energy charge), which has earlier been hypothesized to be decisive for persister formation.

Discussion

The study provides guides and suggestions for the design of future experimentation in the research fields of persisters and antibiotic tolerance.

Nanobiotics against antimicrobial resistance: harnessing the power of nanoscale materials and technologies

Given the spasmodic increment in antimicrobial resistance (AMR), world is on the verge of “post-antibiotic era”. It is anticipated that current SARS-CoV2 pandemic would worsen the situation in future, mainly due to the lack of new/next generation of antimicrobials. In this context, nanoscale materials with antimicrobial potential have a great promise to treat deadly pathogens. These functional materials are uniquely positioned to effectively interfere with the bacterial systems and augment biofilm penetration. Most importantly, the core substance, surface chemistry, shape, and size of nanomaterials define their efficacy while avoiding the development of AMR. Here, we review the mechanisms of AMR and emerging applications of nanoscale functional materials as an excellent substitute for conventional antibiotics. We discuss the potential, promises, challenges and prospects of nanobiotics to combat AMR.

Human serum triggers antibiotic tolerance in Staphylococcus aureus

Staphylococcus aureus frequently causes infections that are challenging to treat, leading to high rates of persistent and relapsing infection. Here, to understand how the host environment influences treatment outcomes, we study the impact of human serum on staphylococcal antibiotic susceptibility. We show that serum triggers a high degree of tolerance to the lipopeptide antibiotic daptomycin and several other classes of antibiotic. Serum-induced daptomycin tolerance is due to two independent mechanisms. Firstly, the host defence peptide LL-37 induces tolerance by triggering the staphylococcal GraRS two-component system, leading to increased peptidoglycan accumulation. Secondly, GraRS-independent increases in membrane cardiolipin abundance are required for full tolerance. When both mechanisms are blocked, S. aureus incubated in serum is as susceptible to daptomycin as when grown in laboratory media. Our work demonstrates that host factors can significantly modulate antibiotic susceptibility via diverse mechanisms, and combination therapy may provide a way to mitigate this.

Application of Special Electron Microscopy Techniques to the Study of DNA - Protein Complexes in E. coli Cells

Various electron microscopy techniques were applied recently to the study of DNA condensation in dormant bacterial cells. Here, we describe, in detail, the preparation of dormant Escherichia coli cells for electron microscopy studies and electron tomography and energy dispersive spectroscopy (EDS) approaches, which were used to reveal the structures of DNA-protein complexes in dormant Escherichia coli cells.

Transcriptional Response of Multidrug-Resistant Klebsiella pneumoniae Clinical Isolates to Ciprofloxacin Stress

Background

The term “persisters” refers to a small bacterial population that persists during treatment with high antibiotic concentration or dose in the absence of genetic resistance. The present study was designed to investigate the transcriptional response in indigenous Klebsiella pneumoniae under the ciprofloxacin stress.

Methods

Isolation and identification of K. pneumoniae were carried out through standard microbiological protocols. The characterization of quinolone resistance was performed by estimating the quinolone susceptibility testing, MIC estimation, and detecting the QRDR and PMQR. Transcriptional response of the isolates to ciprofloxacin was determined using qPCR.

Results

Among 34 isolates, 23 (67%) were resistant to ciprofloxacin. Both QRDR (gyrA and gyrB) and PMQR (qnrA, qnrB, and qnrS) were detected in the isolates, and all were found resistant to ciprofloxacin. The mRNA levels of both mutS and euTu under the influence of ciprofloxacin were significantly increased. On ciprofloxacin exposure, the mRNA levels of the DNA damage response element (mutS) were raised in a time-dependent fashion. K. pneumoniae showed high-level resistance to ciprofloxacin in the presence of mutations in QRDR and PMQR genes.

Conclusion

The transcriptional response revealed the upregulation of DNA repair and protein folding elements (mutS and euTu) in ciprofloxacin stress and delayed cell division. The ciprofloxacin was found to trigger various stress responses in a time- and concentration-dependent manner.

Antimicrobial Resistance and Inorganic Nanoparticles

Antibiotics are being less effective, which leads to high mortality in patients with infections and a high cost for the recovery of health, and the projections that are had for the future are not very encouraging which has led to consider antimicrobial resistance as a global health problem and to be the object of study by researchers. Although resistance to antibiotics occurs naturally, its appearance and spread have been increasing rapidly due to the inappropriate use of antibiotics in recent decades. A bacterium becomes resistant due to the transfer of genes encoding antibiotic resistance. Bacteria constantly mutate; therefore, their defense mechanisms mutate, as well. Nanotechnology plays a key role in antimicrobial resistance due to materials modified at the nanometer scale, allowing large numbers of molecules to assemble to have a dynamic interface. These nanomaterials act as carriers, and their design is mainly focused on introducing the temporal and spatial release of the payload of antibiotics. In addition, they generate new antimicrobial modalities for the bacteria, which are not capable of protecting themselves. So, nanoparticles are an adjunct mechanism to improve drug potency by reducing overall antibiotic exposure. These nanostructures can overcome cell barriers and deliver antibiotics to the cytoplasm to inhibit bacteria. This work aims to give a general vision between the antibiotics, the nanoparticles used as carriers, bacteria resistance, and the possible mechanisms that occur between them.

Do Iron Oxide Nanoparticles Have Significant Antibacterial Properties?

The use of metal oxide nanoparticles is one of the promising ways for overcoming antibiotic resistance in bacteria. Iron oxide nanoparticles (IONPs) have found wide applications in different fields of biomedicine. Several studies have suggested using the antimicrobial potential of IONPs. Iron is one of the key microelements and plays an important role in the function of living systems of different hierarchies. Iron abundance and its physiological functions bring into question the ability of iron compounds at the same concentrations, on the one hand, to inhibit the microbial growth and, on the other hand, to positively affect mammalian cells. At present, multiple studies have been published that show the antimicrobial effect of IONPs against Gram-negative and Gram-positive bacteria and fungi. Several studies have established that IONPs have a low toxicity to eukaryotic cells. It gives hope that IONPs can be considered potential antimicrobial agents of the new generation that combine antimicrobial action and high biocompatibility with the human body. This review is intended to inform readers about the available data on the antimicrobial properties of IONPs, a range of susceptible bacteria, mechanisms of the antibacterial action, dependence of the antibacterial action of IONPs on the method for synthesis, and the biocompatibility of IONPs with eukaryotic cells and tissues.

Detection of bacterial colonization by the spectral changes of surface-enhanced Raman reporters

In times of widespread multiple antibiotic resistance, the bacterial colonization of crucial medical surfaces should be detected as fast as possible. In this work, we present the non-destructive SERS method for the detection of bacterial colonization. SERS is an excellent tool for the monitoring of suitable substances in low concentrations. The SERS substrate was prepared by the aggregation of citrate-stabilized gold nanoparticles and the adsorption of the reporters (crystal violet, thiamine, and adenine). We have tested the substrate for the detection of clinically relevant S. aureus and P. aeruginosa bacteria. The SERS spectra before and after the substrate incubation revealed the degradation of the reporter by the growing bacteria. The growth of P. aeruginosa was detected using the substrates with preadsorbed crystal violet or adenine. The suitable reporter for the detection of S. aureus remains to be discovered. The selection of the reporters resistant to exposure but easily degraded by bacteria will open the way for the in situ monitoring of bacterial colonization, thus complementing the arsenal of methods in the battle against hospital infections.

Directed evolution reveals the mechanism of HitRS signaling transduction in Bacillus anthracis

Two component systems (TCSs) are a primary mechanism of signal sensing and response in bacteria. Systematic characterization of an entire TCS could provide a mechanistic understanding of these important signal transduction systems. Here, genetic selections were employed to dissect the molecular basis of signal transduction by the HitRS system that detects cell envelope stress in the pathogen Bacillus anthracis. Numerous point mutations were isolated within HitRS, 17 of which were in a 50-residue HAMP domain. Mutational analysis revealed the importance of hydrophobic interactions within the HAMP domain and highlighted its essentiality in TCS signaling. In addition, these data defined residues critical for activities intrinsic to HitRS, uncovered specific interactions among individual domains and between the two signaling proteins, and revealed that phosphotransfer is the rate-limiting step for signal transduction. Furthermore, this study establishes the use of unbiased genetic selections to study TCS signaling and provides a comprehensive mechanistic understanding of an entire TCS.

Bacterial TCSs are a primary strategy for stress sensing and niche adaptation. Although individual domains and proteins of these systems have been extensively studied, systematic characterization of an entire TCS is rare. In this study, through unbiased genetic selections and rigorous biochemical analysis, we provide a detailed characterization and structure-function analysis of an entire TCS and extend our understanding of the molecular basis of signal transduction through TCSs. Moreover, this study provides a comprehensive map of point-mutations in these well-conserved signaling proteins, which will be broadly useful for studying other TCSs. The described genetic selection strategies are applicable to any TCS, providing a powerful tool for researchers interested in microbial signal transduction.

Morphological peculiarities of the DNA-protein complexes in starved Escherichia coli cells

One of the adaptive strategies for the constantly changing conditions of the environment utilized in bacterial cells involves the condensation of DNA in complex with the DNA-binding protein, Dps. With the use of electron microscopy and electron tomography, we observed several morphologically different types of DNA condensation in dormant Escherichia coli cells, namely: nanocrystalline, liquid crystalline, and the folded nucleosome-like. We confirmed the presence of both Dps and DNA in all of the ordered structures using EDX analysis. The comparison of EDX spectra obtained for the three different ordered structures revealed that in nanocrystalline formation the majority of the Dps protein is tightly bound to nucleoid DNA. The dps-null cells contained only one type of condensed DNA structure, liquid crystalline, thus, differing from those with Dps. The results obtained here shed some light on the phenomenon of DNA condensation in dormant prokaryotic cells and on the general problem of developing a response to stress. We demonstrated that the population of dormant cells is structurally heterogeneous, allowing them to respond flexibly to environmental changes. It increases the ability of the whole bacterial population to survive under extreme stress conditions.

Regenerative Adaptation to Electrochemical Perturbation in Planaria: A Molecular Analysis of Physiological Plasticity

Anatomical homeostasis results from dynamic interactions between gene expression, physiology, and the external environment. Owing to its complexity, this cellular and organism-level phenotypic plasticity is still poorly understood. We establish planarian regeneration as a model for acquired tolerance to environments that alter endogenous physiology. Exposure to barium chloride (BaCl₂) results in a rapid degeneration of anterior tissue in Dugesia japonica. Remarkably, continued exposure to fresh solution of BaCl₂ results in regeneration of heads that are insensitive to BaCl₂. RNA-seq revealed transcriptional changes in BaCl₂-adapted heads that suggests a model of adaptation to excitotoxicity. Loss-of-function experiments confirmed several predictions: blockage of chloride and calcium channels allowed heads to survive initial BaCl₂ exposure, inducing adaptation without prior exposure, whereas blockade of TRPM channels reversed adaptation. Such highly adaptive plasticity may represent an attractive target for biomedical strategies in a wide range of applications beyond its immediate relevance to excitotoxicity preconditioning.

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Exposure to BaCl₂ causes the heads of Dugesia japonica to degenerate

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Prolonged exposure to BaCl₂ results in regeneration of a BaCl₂-insensitive head

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Ion channel expression is altered in the head to compensate for excitotoxic stress

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TRPMa is upregulated in BaCl₂-treated animals; blocking TRPM prevents adaptation

Molecular Mechanisms of Bacterial Resistance to Metal and Metal Oxide Nanoparticles

The increase in bacterial resistance to one or several antibiotics has become a global health problem. Recently, nanomaterials have become a tool against multidrug-resistant bacteria. The metal and metal oxide nanoparticles are one of the most studied nanomaterials against multidrug-resistant bacteria. Several in vitro studies report that metal nanoparticles have antimicrobial properties against a broad spectrum of bacterial species. However, until recently, the bacterial resistance mechanisms to the bactericidal action of the nanoparticles had not been investigated. Some of the recently reported resistance mechanisms include electrostatic repulsion, ion efflux pumps, expression of extracellular matrices, and the adaptation of biofilms and mutations. The objective of this review is to summarize the recent findings regarding the mechanisms used by bacteria to counteract the antimicrobial effects of nanoparticles.

Dismantling the bacterial virulence program

In the face of rising antimicrobial resistance, there is an urgent need for the development of efficient and effective anti-infective compounds. Adaptive resistance, a reversible bacterial phenotype characterized by the ability to surmount antibiotic challenge without mutation, is triggered to cope in situ with several stressors and is very common clinically. Thus, it is important to target stress-response effectors that contribute to in vivo adaptations and associated lifestyles such as biofilm formation. Interfering with these proteins should provide a means of dismantling bacterial virulence for treating infectious diseases, in combination with conventional antibiotics.