Unprecedented Silver Resistance in Clinically Isolated Enterobacteriaceae: Major Implications for Burn and Wound Management

Nanocomposites: silver nanoparticles and bacteriocins obtained from lactic acid bacteria against multidrug-resistant Escherichia coli and Staphylococcus aureus

Drug-resistant bacteria such as Escherichia coli and Staphylococcus aureus represent a global health problem that requires priority attention. Due to the current situation, there is an urgent need to develop new, more effective and safe antimicrobial agents. Biotechnological approaches can provide a possible alternative control through the production of new generation antimicrobial agents, such as silver nanoparticles (AgNPs) and bacteriocins. AgNPs stand out for their antimicrobial potential by employing several mechanisms of action that can act simultaneously on the target cell such as the production of reactive oxygen species and cell wall rupture. On the other hand, bacteriocins are natural peptides synthesized ribosomally that have antimicrobial activity and are produced, among others, by lactic acid bacteria (LAB), whose main mechanism of action is to produce pores at the level of the cell membrane of bacterial cells. However, these agents have disadvantages. Nanoparticles also have limitations such as the tendency to form aggregates, which decreases their antibacterial activity and possible cytotoxic effects, and bacteriocins have a narrow spectrum of action, require high doses to be effective, and can be degraded by proteases. Given these limitations, nanoconjugates of these two agents have been developed that can act synergistically in the control of pathogenic bacteria resistant to antibiotics. This review focuses on knowing relevant aspects of the antibiotic resistance of E. coli and S. aureus, the characteristics of these new generation antibacterial agents, and their effect alone or forming nanoconjugates that are more effective against the multiresistant mentioned bacteria.

A novel hydrogel with inherent antibacterial and hemostatic properties for burn wound healing

The skin is the immune system's first line of defense. Extensive skin burns can lead to tissue necrosis, sepsis, and even death. Anti-infectious care of burn wounds is a major challenge in clinical medicine. However, the extensive use of antibiotics led to the emergence of multi-drug-resistant bacteria and silver dressings with antibacterial effects are also cytotoxic. We used the natural cationic antibacterial agent ε-polylysine (EPL) to graft Epigallocatechin-3-gallate (EGCG) to synthesize EPL-EGCG. Then, we used methacrylated gelatin (GelMA) with arginine-glycine-aspartate-rich acid (RGD) sequence and EPL-EGCG form interpenetrating polymer network hydrogels with excellent swelling properties. The hydrogel's inherent antibacterial properties and photo-cross-linking properties can cover irregular burn wounds and isolate bacteria to prevent infection. In addition, we used polydopamine (PDA) to coat GelMA microspheres with excellent hemostatic efficacy and load platelet-rich plasma (PRP) to enhance the hemostatic efficacy of the microspheres and impart inflammation-regulating functions. The hydrogel showed excellent hemostatic efficacy in rat liver injury and tail vein injury models. In the rat infected burn model, the hydrogel exhibited favorable antimicrobial, pro-angiogenic, and anti-inflammatory phenotype polarization of macrophages. Our study shows that GelMA/EPL-EGCG/GM-PDA@PRP hydrogel application has excellent antibacterial, hemostatic and anti-inflammatory effects, providing a new treatment strategy for wound care before burn skin grafting.

Variable effects of exposure to ionic silver in wound-associated bacterial pathogens

Silver compounds are used in wound dressings to reduce bioburden. Where infection is not rapidly resolved, bacteria may be exposed to sub-therapeutic concentrations of antimicrobials over prolonged periods of time. In this study, a panel of chronic wound bacteria, Pseudomonas aeruginosa (two strains), Staphylococcus aureus, and Escherichia coli, were exposed to silver nitrate on agar. Phenotypic characterization was achieved using broth microdilution sensitivity testing, a crystal violet biofilm assay, and a wax moth pathogenesis model. Repeated exposure to ionic silver did not result in planktonic phenotypic silver resistance in any of the test panels, although S. aureus demonstrated reversible increases in minimum bactericidal concentration. An ulcer-derived P. aeruginosa exhibited marked reductions in biofilm eradication concentration as well as significantly increased biofilm formation and wax moth killing when compared to the same progenitor. These changes were reversible, trending towards baseline measurements following 10 passages on silver-free media. Changes in virulence and biofilm formation in the other test bacteria were generally limited. In summary, phenotypic adaptation following exposure to ionic silver was manifested other than through changes in planktonic susceptibility. Significant changes in pseudomonas biofilm formation and sensitivity could have implications for wound care regimes and therefore warrant further investigation.

In vitro prevention and inactivation of biofilms using controlled-release iodine foam dressings for wound healing

Microbial biofilms are a major hindrance in the wound healing process, prolonging the inflammatory response phase, thus making them a target in treatment. The aim of this study is to assess the antibacterial properties of commercially available wound dressings, of various material composition and antibacterial agents, towards multiple in vitro microbial and biofilm models. A variety of in vitro microbial and biofilm models were utilised to evaluate the ability of wound dressing materials to sequester microbes, prevent dissemination and manage bioburden. Sequestering and dissemination models were used to evaluate the ability of wound dressing materials to prevent the biofilm-forming bacterium, Pseudomonas aeruginosa, from migrating through dressing materials over a 24-72 h challenge period. Additionally, Centre for Disease Control (CDC) Bioreactor and Drip Flow models were used to evaluate antibacterial killing efficacy towards established P. aeruginosa and Staphylococcus aureus biofilms using more challenging, wound-like models. Controlled-release iodine foam and silver-impregnated carboxymethylcellulose (CMC) wound dressing materials demonstrated potent biofilm management properties in comparison to a methylene blue and gentian violet-containing foam dressing. Both the iodine-containing foam and silver-impregnated CMC materials effectively prevented viable P. aeruginosa dissemination for up to 72 h. In addition, the controlled-release iodine foam and silver-impregnated CMC materials reduced P. aeruginosa bioburden in the Drip Flow model. The controlled-release iodine foam demonstrated superiority in the CDC Bioreactor model, as both the silver- and iodine-containing materials reduced S. aureus to the limit of detection, but P. aeruginosa growth was only completely reduced by controlled-release iodine foam dressing materials. The data generated within the in vitro biofilm models supports the clinical data available in the public domain for the implementation of iodine foam dressings for effective biofilm management and control in wound care.

Alleviating the virulence of Pseudomonas aeruginosa and Staphylococcus aureus by ascorbic acid nanoemulsion

The high incidence of persistent multidrug resistant bacterial infections is a worldwide public health burden. Alternative strategies are required to deal with such issue including the use of drugs with anti-virulence activity. The application of nanotechnology to develop advanced Nano-materials that target quorum sensing regulated virulence factors is an attractive approach. Synthesis of ascorbic acid Nano-emulsion (ASC-NEs) and assessment of its activity in vitro against the virulence factors and its protective ability against pathogenesis as well as the effect against expression of quorum sensing genes of Pseudomonas aeruginosa and Staphylococcus aureus isolates. Ascorbic acid Nano-emulsion was characterized by DLS Zetasizer Technique, Zeta potential; Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The antibacterial activity of ASC-NEs was tested by the broth microdilution method and the activity of their sub-MIC against the expression of quorum sensing controlled virulence was investigated using phenotypic experiments and RT-PCR. The protective activity of ASC-NEs against P. aeruginosa as well as S. aureus pathogenesis was tested in vivo. Phenotypically, ASC-NEs had strong virulence inhibitory activity against the tested bacteria. The RT-PCR experiment showed that it exhibited significant QS inhibitory activity. The in vivo results showed that ASC-NEs protected against staphylococcal infection, however, it failed to protect mice against Pseudomonal infection. These results suggest the promising use of nanoformulations against virulence factors in multidrug resistant P. aeruginosa and S. aureus. However, further studies are required concerning the potential toxicity, clearance and phamacokinetics of the nanoformulations.

What happens when nanoparticles encounter bacterial antibiotic resistance?

Bacterial resistance to antibiotics has become a widespread concern, and poses serious environmental and global health problems. Lots of studies have demonstrated that engineered nanoparticles (NPs) can significantly affect bacterial antibiotic resistance; however, whether NPs promote or inhibit antibiotic resistance remains a complex and well-debated issue. This will constrain environmental antibiotic resistance gene contamination and clinical bacterial resistance problems, resulting in unclear and poorly targeted treatment efficacy. To better understand the relationship between NPs and antibiotic resistance, this review systematically summarizes and reanalyzes published data on the effect of NPs on bacterial antibiotic resistance and related mechanisms. The effects of intrinsic properties of NPs, such as size, concentration, functional groups, and extrinsic properties of NPs on the development of antibiotic resistance were dissected. This review will provide a better understanding of the effects of increasingly released NPs in different environments on bacterial resistance and underlines the direction for employing NPs to control the dissemination of antibiotic resistance genes in the environment. Next, how NPs affect intracellular and extracellular antibiotic resistance needs in-depth exploration. Besides, alternative treatments of NPs and antibiotics in therapy will be a future trend for combating antibiotic resistance, and the follow-up emphasis should determine their dose effects and potential mechanism. This study will expand our understanding of the biosafety of nanomaterials and provides a theoretical reference to guide the proper application of nanomaterials or technologies to environmental pollution control and clinical treatment.

Review of Antimicrobial Nanocoatings in Medicine and Dentistry: Mechanisms of Action, Biocompatibility Performance, Safety, and Benefits Compared to Antibiotics

This review discusses topics relevant to the development of antimicrobial nanocoatings and nanoscale surface modifications for medical and dental applications. Nanomaterials have unique properties compared to their micro- and macro-scale counterparts and can be used to reduce or inhibit bacterial growth, surface colonization and biofilm development. Generally, nanocoatings exert their antimicrobial effects through biochemical reactions, production of reactive oxygen species or ionic release, while modified nanotopographies create a physically hostile surface for bacteria, killing cells via biomechanical damage. Nanocoatings may consist of metal nanoparticles including silver, copper, gold, zinc, titanium, and aluminum, while nonmetallic compounds used in nanocoatings may be carbon-based in the form of graphene or carbon nanotubes, or composed of silica or chitosan. Surface nanotopography can be modified by the inclusion of nanoprotrusions or black silicon. Two or more nanomaterials can be combined to form nanocomposites with distinct chemical or physical characteristics, allowing combination of different properties such as antimicrobial activity, biocompatibility, strength, and durability. Despite their wide range of applications in medical engineering, questions have been raised regarding potential toxicity and hazards. Current legal frameworks do not effectively regulate antimicrobial nanocoatings in matters of safety, with open questions remaining about risk analysis and occupational exposure limits not considering coating-based approaches. Bacterial resistance to nanomaterials is also a concern, especially where it may affect wider antimicrobial resistance. Nanocoatings have excellent potential for future use, but safe development of antimicrobials requires careful consideration of the "One Health" agenda, appropriate legislation, and risk assessment.

Antimicrobial Drug Resistance in Poultry Production: Current Status and Innovative Strategies for Bacterial Control

The world population’s significant increase has promoted a higher consumption of poultry products, which must meet the specified demand while maintaining their quality and safety. It is well known that conventional antimicrobials (antibiotics) have been used in livestock production, including poultry, as a preventive measure against or for the treatment of infectious bacterial diseases. Unfortunately, the use and misuse of these compounds has led to the development and dissemination of antimicrobial drug resistance, which is currently a serious public health concern. Multidrug-resistant bacteria are on the rise, being responsible for serious infections in humans and animals; hence, the goal of this review is to discuss the consequences of antimicrobial drug resistance in poultry production, focusing on the current status of this agroeconomic sector. Novel bacterial control strategies under investigation for application in this industry are also described. These innovative approaches include antimicrobial peptides, bacteriophages, probiotics and nanoparticles. Challenges related to the application of these methods are also discussed.

Zinc-Based Nanoparticles Reduce Bacterial Biofilm Formation

Biofilm formation is important for microbial survival in hostile environments and a phenotype that provides microorganisms with antimicrobial resistance. Zinc oxide (ZnO) and Zinc sulfide (ZnS) nanoparticles (NPs) present potential antimicrobial properties for biomedical and food industry applications. Here, we aimed to analyze, for the first time, the bactericidal and antibiofilm activity of ZnS NPs against Staphylococcus aureus, Klebsiella oxytoca, and Pseudomonas aeruginosa, all medically important bacteria in developed countries. We compared ZnS NPs antimicrobial activity to ZnO NPs, which have been extensively studied. Using the colorimetric XTT reduction assay to observe the metabolic activity of bacterial cells and the crystal violet assay to measure biofilm mass, we demonstrated that ZnS and ZnO had similar efficacy in killing planktonic bacterial cells and reducing biofilm formation, with S. aureus being more susceptible to both therapeutics than K. oxytoca and P. aeruginosa. Crystal violet staining and confocal microscopy validated that Zn NPs inhibit biofilm formation and cause architectural damage. Our findings provide proof of principle that ZnS NPs have antibiofilm activity, and can be potentially used in medical and food industry applications, such as treatment of wound infections or package coating for food preservation. IMPORTANCE Zinc (Zn)-based nanoparticles (NPs) can be potentially used in medical and food preservation applications. As proof of principle, we investigated the bactericidal and antibiofilm activity of zinc oxide (ZnO) and zinc sulfide (ZnS) NPs against medically important bacteria. Zn-based NPs were similarly effective in killing planktonic and biofilm-associated Staphylococcus aureus, Klebsiella oxytoca, and Pseudomonas aeruginosa cells. However, S. aureus was more susceptible to these investigational therapeutics. Although further studies are warranted, our findings suggest the possibility of future use of Zn-based NPs in the treatment of skin infections or preservation of food.

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

Biocidal Activity of Tannic Acid-Prepared Silver Nanoparticles towards Pathogens Isolated from Patients with Exacerbations of Chronic Rhinosinusitis

The microbiome's significance in chronic rhinosinusitis (CRS) is unclear. Antimicrobials are recommended in acute exacerbations of the disease (AECRS). Increasing rates of antibiotic resistance have stimulated research on alternative therapeutic options, including silver nanoparticles (AgNPs). However, there are concerns regarding the safety of silver administration. The aim of this study was to assess the biological activity of tannic acid-prepared AgNPs (TA-AgNPs) towards sinonasal pathogens and nasal epithelial cells (HNEpC). The minimal inhibitory concentration (MIC) for pathogens isolated from patients with AECRS was approximated using the well diffusion method. The cytotoxicity of TA-AgNPswas evaluated using an MTT assay and trypan blue exclusion. A total of 48 clinical isolates and 4 reference strains were included in the study (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Klebsiellaoxytoca, Acinetobacter baumannii, Serratia marcescens, Enterobacter cloacae). The results of the studies revealed that the MIC values differed between isolates, even within the same species. All the isolates were sensitive to TA-AgNPs in concentrations non-toxic to human cells during 24 h exposition. However, 48 h exposure to TA-AgNPs increased toxicity to HNEpC, narrowing their therapeutic window and enabling 19% of pathogens to resist the TA-AgNPs' biocidal action. It was concluded that TA-AgNPs are non-toxic for the investigated eukaryotic cells after short-term exposure and effective against most pathogens isolated from patients with AECRS, but sensitivity testing may be necessary before application.

The Potential of Antibiotics and Nanomaterial Combinations as Therapeutic Strategies in the Management of Multidrug-Resistant Infections: A Review

Antibiotic resistance has become a major public health concern around the world. This is exacerbated by the non-discovery of novel drugs, the development of resistance mechanisms in most of the clinical isolates of bacteria, as well as recurring infections, hindering disease treatment efficacy. In vitro data has shown that antibiotic combinations can be effective when microorganisms are resistant to individual drugs. Recently, advances in the direction of combination therapy for the treatment of multidrug-resistant (MDR) bacterial infections have embraced antibiotic combinations and the use of nanoparticles conjugated with antibiotics. Nanoparticles (NPs) can penetrate the cellular membrane of disease-causing organisms and obstruct essential molecular pathways, showing unique antibacterial mechanisms. Combined with the optimal drugs, NPs have established synergy and may assist in regulating the general threat of emergent bacterial resistance. This review comprises a general overview of antibiotic combinations strategies for the treatment of microbial infections. The potential of antibiotic combinations with NPs as new entrants in the antimicrobial therapy domain is discussed.

Chemorepellent-Loaded Nanocarriers Promote Localized Interference of Escherichia coli Transport to Inhibit Biofilm Formation

To mitigate antimicrobial resistance, we developed polymeric nanocarrier delivery of the chemorepellent signaling agent, nickel, to interfere with Escherichia coli transport to a surface, an incipient biofilm formation stage. The dynamics of nickel nanocarrier (Ni NC) chemorepellent release and induced chemorepellent response required to effectively modulate bacterial transport for biofilm prevention were characterized in this work. Ni NCs were fabricated with the established Flash NanoPrecipitation method. NC size was characterized with dynamic light scattering. Measured with a zincon monosodium salt colorimetric assay, NC nickel release was pH-dependent, with 62.5% of total encapsulated nickel released at pH 7 within 0-15 min, competitive with rapid E. coli transport to the surface. Confocal laser scanning microscopy of E. coli (GFP-expressing) biofilm growth dynamics on fluorescently labeled Ni NC coated glass coupled with a theoretical dynamical criterion probed the biofilm prevention outcomes of NC design. The Ni NC coating significantly reduced E. coli attachment compared to a soluble nickel coating and reduced E. coli biomass area by 61% compared to uncoated glass. A chemical-in-plug assay revealed Ni NCs induced a chemorepellent response in E. coli. A characteristic E. coli chemorepellent response was observed away from the Ni NC coated glass over 10 μm length scales effective to prevent incipient biofilm surface attachment. The dynamical criterion provided semiquantitative analysis of NC mechanisms to control biofilm and informed optimal chemorepellent release profiles to improve NC biofilm inhibition. This work is fundamental for dynamical informed design of biofilm-inhibiting chemorepellent-loaded NCs promising to mitigate the development of resistance and interfere with the transport of specific pathogens.

The Impact of Antiseptic-Loaded Bacterial Nanocellulose on Different Biofilms-An Effective Treatment for Chronic Wounds?

Introduction: Pathogenic biofilms are an important factor for impaired wound healing, subsequently leading to chronic wounds. Nonsurgical treatment of chronic wound infections is limited to the use of conventional systemic antibiotics and antiseptics. Wound dressings based on bacterial nanocellulose (BNC) are considered a promising approach as an effective carrier for antiseptics. The aim of the present study was to investigate the antimicrobial activity of antiseptic-loaded BNC against in vitro biofilms. Materials and Methods: BNC was loaded with the commercially available antiseptics Prontosan^® and Octenisept^®. The silver-based dressing Aquacel^®Ag Extra was used as a positive control. The biofilm efficacy of the loaded BNC sheets was tested against an in vitro 24-hour biofilm of Staphylococcus aureus and Candida albicans and a 48-hour biofilm of Pseudomonas aeruginosa. In vivo tests using a porcine excisional wound model was used to analyze the effect of a prolonged treatment with the antiseptics on the healing process. Results: We observed complete eradication of S. aureus biofilm in BNC loaded with Octenisept^® and C. albicans biofilm for BNC loaded with Octenisept^® or Prontosan^®. Treatment with unloaded BNC also resulted in a statistically significant reduction in bacterial cell density of S. aureus compared to untreated biofilm. No difference on the wound healing outcome was observed for the wounds treated for seven days using BNC alone in comparison to BNC combined with Prontosan^® or with Octenisept^®. Conclusions: Based on these results, antiseptic-loaded BNC represents a promising and effective approach for the treatment of biofilms. Additionally, the prolonged exposure to the antiseptics does not affect the healing outcome. Prevention and treatment of chronic wound infections may be feasible with this novel approach and may even be superior to existing modalities.

Identification of a Novel IncHI1B Plasmid in MDR Klebsiella pneumoniae 200 from Swine in China

Multidrug-resistant (MDR) Klebsiella pneumoniae poses a seriously threat to public health. The aim of this study was to better understand the genetic structure of its plasmids and chromosomes. The whole-genome sequence of K. pneumoniae 200 isolated from the liver of a swine with diarrhea in China was determined using PacBio RS II and Illumina MiSeq sequencing. The complete sequences of the chromosomal DNA and the plasmids were analyzed for the presence of resistance genes. The phylogenetic trees revealed that K. pneumoniae 200 displayed the closest relationship to a human-associated K. pneumoniae strain from Thailand. K. pneumoniae 200 contained two plasmids, pYhe2001 and pYhe2002, belonging to the incompatibility groups IncH-HI1B and IncF-FIA. The plasmid pYhe2001 was a novel plasmid containing four types of heavy metal resistance genes and a novel Tn6897 transposon flanked by two copies of IS26 at both ends. Mixed plasmids could be transferred from K. pneumoniae 200 to Escherichia coli DH5α through transformation together. This study reported the first time a novel plasmid pYhe2001 from swine origin K. pneumoniae 200, suggesting that the plasmids may act as reservoirs for various antimicrobial resistance genes and transport multiple resistance genes in K. pneumoniae of both animal and human origin.

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.

Metal nanoparticles and nanoparticle composites are effective against Haemophilus influenzae, Streptococcus pneumoniae, and multidrug-resistant bacteria

BACKGROUND

Treatment for lower respiratory tract infection caused by multidrug-resistant organisms (MDRO) are often limited. This study explored the activity of different metal nanoparticles against several respiratory pathogens including MDROs.

METHODS

Clinical isolates of carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Klebsiella pneumoniae (CRKP), Pseudomonas aeruginosa, Haemophilus influenzae, methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus pneumoniae were tested for in vitro susceptibilities to various antibiotics and nanoparticles. Minimum inhibitory concentrations (MICs) of silver-nanoparticle (Ag-NP), selenium-nanoparticle (Se-NP), and three composites solutions ND50, NK99, and TPNT1 (contained 5 ppm Ag-NP, 60 ppm ZnO-nanoparticle, and different concentrations of gold-nanoparticle or ClO₂) were determined by broth microdilution method.

RESULTS

Fifty isolates of each bacterial species listed above were tested. Ag-NP showed lower MICs to all species than Se-NP. The MIC₅₀s of Ag-NP for CRAB, CRKP, P. aeruginosa, and H. influenzae were <3.125 ppm, 25 ppm, <3.125 ppm, and <3.125 ppm, respectively, while those for S. pneumoniae and MRSA were >50 ppm and 50 ppm. Among CRAB, CRKP and P. aeruginosa, the MIC₅₀s of ND50, NK99, and TPNT1 for CRAB were the lowest (1/8 dilution, 1/8 dilution, and 1/8 dilution, respectively), and those for CRKP (>1/2 dilution, 1/2 dilution, and 1/2 dilution, respectively) were the highest. Both MRSA and S. pneumoniae showed high MIC₅₀s to ND50, NK99, and TPNT1.

CONCLUSIONS

Metal nanoparticles had good in vitro activity against Gram-negative bacteria. They might be suitable to be prepared as environmental disinfectants or inhaled agents to inhibit the growth of MDR Gram-negative colonizers in the lower respiratory tracts of patients with chronic lung diseases.

Topical Wound Therapy Products With Ionic Silver: A Technologic Analysis

PURPOSE

The purpose of this technologic analysis was to review use of ionic silver as a component of topical wound therapy products.

APPROACH

Published literature from a variety of fields related to ionic silver and its use in topical wound therapy products was reviewed and a summary of common commercially available wound care products containing ionic silver was generated, along with general recommendations for use. Safety information from both manufacturer guidelines and the Manufacturer and User Facility Device Experience (MAUDE) database is summarized.

CONCLUSIONS

Various formulations of ionic silver products are used for topical treatment of wounds. Antimicrobial activity varies according to the specific silver formulation and type of microorganisms in the wound bed. In vitro evidence suggests that some bacterial strains may be developing resistance to ionic silver. Improved knowledge of the benefits and safety precautions associated with topical silver preparations can guide its application to topical therapy for wound healing.

Safer plant-based nanoparticles for combating antibiotic resistance in bacteria: A comprehensive review on its potential applications, recent advances, and future perspective

BACKGROUND

Antibiotic resistance is one of the current threats to human health, forcing the use of drugs that are more noxious, costlier, and with low efficiency. There are several causes behind antibiotic resistance, including over-prescription of antibiotics in both humans and livestock. In this scenario, researchers are shifting to new alternatives to fight back this concerning situation.

SCOPE AND APPROACH

Nanoparticles have emerged as new tools that can be used to combat deadly bacterial infections directly or indirectly to overcome antibiotic resistance. Although nanoparticles are being used in the pharmaceutical industry, there is a constant concern about their toxicity toward human health because of the involvement of well-known toxic chemicals (i.e., sodium/potassium borohydride) making their use very risky for eukaryotic cells.

KEY FINDINGS AND CONCLUSIONS

Multiple nanoparticle-based approaches to counter bacterial infections, providing crucial insight into the design of elements that play critical roles in the creation of antimicrobial nanotherapeutic drugs, are currently underway. In this context, plant-based nanoparticles will be less toxic than many other forms, which constitute promising candidates to avoid widespread damage to the microbiome associated with current practices. This article aims to review the actual knowledge on plant-based nanoparticle products for antibiotic resistance and the possible replacement of antibiotics to treat multidrug-resistant bacterial infections.

First Report on the Phenotypic and Genotypic Susceptibility Profiles to Silver Nitrate in Bacterial Strains Isolated from Infected Leg Ulcers in Romanian Patients

Silver-ion-based antiseptics are widely used in treating chronic leg ulcers and, given the emergence of resistance to such compounds, the investigation of silver susceptibility and resistance profiles of pathogenic strains isolated from this type of wound is a topic of great interest. Therefore, in this study, 125 bacterial strains isolated from 103 patients with venous ulcers were investigated to elucidate their susceptibility to silver-nitrate solutions in planktonic and biofilm growth states, and the associated genetic determinants. The isolated strains, both in the planktonic and biofilm growth phases, showed high sensitivity to the standard concentration of 1/6000 silver-nitrate solution. It was noticed that even at concentrations lower than the clinical one (the first 2–3 binary dilutions in the case of planktonic cultures and the first 6–7 binary dilutions in the case of biofilms), the antiseptic solution proved to maintain its antibacterial activity. The phenotypic results were correlated with the genetic analysis, highlighting the presence of silver-resistance genes (sil operon) in only a few of the tested Staphylococcus sp. (especially in S. aureus) strains, Escherichia coli and Pseudomonas aeruginosa strains. These results demonstrate that despite its large use, this antiseptic remains a viable treatment alternative for the management of chronic leg wounds.

Mutations in SilS and CusS/OmpC represent different routes to achieve high level silver ion tolerance in Klebsiella pneumoniae

Background

Silver ions have potent broad-spectrum antimicrobial activity and are widely incorporated into a variety of products to limit bacterial growth. In Enterobacteriaceae, decreased silver susceptibility has been mapped to two homologous operons; the chromosomally located cus operon and the plasmid based sil operon. Here we characterised the mechanisms and clinical impact of induced silver tolerance in Klebsiella pneumoniae.

Results

In K. pneumoniae carriage of the sil operon alone does not give elevated silver tolerance. However, when exposed to increasing concentrations of silver nitrate (AgNO₃), K. pneumoniae strains which contain the sil operon, will preferentially mutate SilS, resulting in overexpression of the genes encoding the RND efflux pump silCBA. Those strains which do not carry the sil operon also adapt upon exposure to increasing silver concentrations through mutations in another two-component regulator CusS. Secondary mutations leading to disruption of the outer membrane porin OmpC were also detected. Both routes result in a high level of silver tolerance with MIC’s of >512 mg/L. When exposed to a high concentration of AgNO₃ (400 mg/L), only strains that contained the sil operon were able to survive, again through mutations in SilS. The AgNO₃ adapted strains were also resistant to killing by challenge with several clinical and commercial silver containing dressings.

Conclusions

This study shows that K. pneumoniae has two possible pathways for development of increased silver tolerance but that the sil operon is preferentially mutated. This operon is essential when K. pneumoniae is exposed to high concentrations of silver. The potential clinical impact on wound management is shown by the increased survivability of these adapted strains when exposed to several silver impregnated dressings. This would make infections with these strains more difficult to treat and further limits our therapeutic options.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02532-y.

Nanoantibiotics to fight multidrug resistant infections by Gram-positive bacteria: hope or reality?

The spread of antimicrobial resistance in Gram-positive pathogens represents a threat to human health. To counteract the current lack of novel antibiotics, alternative antibacterial treatments have been increasingly investigated. This review covers the last decade's developments in using nanoparticles as carriers for the two classes of frontline antibiotics active on multidrug-resistant Gram-positive pathogens, i.e., glycopeptide antibiotics and daptomycin. Most of the reviewed papers deal with vancomycin nanoformulations, being teicoplanin- and daptomycin-carrying nanosystems much less investigated. Special attention is addressed to nanoantibiotics used for contrasting biofilm-associated infections. The status of the art related to nanoantibiotic toxicity is critically reviewed.

Characterization of Silver Resistance and Coexistence of sil Operon with Antibiotic Resistance Genes Among Gram-Negative Pathogens Isolated from Wound Samples by Using Whole-Genome Sequencing

Purpose

Methods

Results

Conclusion

Antimicrobial stewardship: wound treatment challenges

The issues with silver resistance and the effectiveness of using DACC-coated dressings in wound treatment were discussed at an Essity-sponsored symposium. Camila Fronzo noted the key points presented by three speakers at the EWMA and Journées Cicatrisations conference 2021 This conference report presents an overview of the symposium 'Being smart about wound infection: evaluating and treating wounds in the era of antimicrobial stewardship', held in October 2021 as part of the joint European Wound Management Association (EWMA) and Journées Cicatrisations virtual conference. The first speaker, Hadar Lev-Tov, talked about the rising problem of silver resistance in wound care, and presented published data that show a general bacterial resistance against silver dressings. The next speaker, Cornelia Wiegand, explained the antimicrobial activity in Cutimed Sorbact dressings (Essity) against five top World Health Organization (WHO)-relevant pathogens, for which new antibiotics are urgently needed. The third and final speaker, Ewa Klara Stürmer, presented six case studies showing the use of Cutimed Sorbact to control bacteria and biofilm on hard-to-heal (a term which has replaced 'chronic') leg ulcers. These demonstrated the effectiveness of Sorbact when managing such wounds.

Benefits of Usage of Immobilized Silver Nanoparticles as Pseudomonas aeruginosa Antibiofilm Factors

The aim of this study was to assess the beneficial inhibitory effect of silver nanoparticles immobilized on SiO2 or TiO2 on biofilm formation by Pseudomonas aeruginosa-one of the most dangerous pathogens isolated from urine and bronchoalveolar lavage fluid of patients hospitalized in intensive care units. Pure and silver doped nanoparticles of SiO2 and TiO2 were prepared using a novel modified sol-gel method. Ten clinical strains of P. aeruginosa and the reference PAO1 strain were used. The minimal inhibitory concentration (MIC) was determined by the broth microdilution method. The minimal biofilm inhibitory concentration (MBIC) and biofilm formation were assessed by colorimetric assay. Bacterial enumeration was used to assess the viability of bacteria in the biofilm. Silver nanoparticles immobilized on the SiO2 and TiO2 indicated high antibacterial efficacy against P. aeruginosa planktonic and biofilm cultures. TiO2/Ag0 showed a better bactericidal effect than SiO2/Ag0. Our results indicate that the inorganic compounds (SiO2, TiO2) after nanotechnological modification may be successfully used as antibacterial agents against multidrug-resistant P. aeruginosa strains.

Co-transfer of plasmid-encoded bla carbapenemases genes and mercury resistance operon in high-risk clones of Klebsiella pneumoniae

Carbapenemase-producing Klebsiella pneumoniae (CP-Kp) is a real global health threat. Environmental reservoirs of resistance gene determinats, such as effluents of hospital wastewaters, are acquiring increased relevance in the selection of plasmid-encoded carbapenemase genes. The presence of Hg in environmental reservoirs may exert a positive selective pressure on tolerant bacteria, favoring the co-transfer of carbapenemase genes and mer operons. In our study, 63 CP-Kp isolates were screened for mer operons by whole genome sequencing (MySeq). Conjugation assays were performed with 24 out of 63 CP-Kp isolates harboring the mer operon. Ten transconjugants (Tc-Kp) were selected with Hg. Plasmid DNA of Tc-Kp was extracted and sequenced using single-molecule real-time (SMRT) technology (PacBio, Sequel II system) with later annotation. Plasmid analysis revealed that Tc-Kp from bla_IMP-like (n = 3) showed a single plasmid belonging to IncC group with two complete mer operon next to bla_IMP-like. Tc-Kp from bla_VIM-1 (n = 2) harbored two plasmids, one with bla_VIM-1 in an IncL, and mer operon was in an IncFIB plasmid. Tc-Kp from bla_OXA-48-like (n = 5) showed 2 plasmids. bla_OXA-48-like was found in an IncL plasmid, whereas mer operon was (i) in an IncR plasmid associated with bla_CTX-M-15 in 3 Tc-Kp-OXA-48-like, (ii) in an IncC plasmid associated with bla_CMY-2 in 1 Tc-Kp-OXA-48-like, (iii) and in an IncFIB plasmid associated with bla_CTX-M-15 in 1 Tc-Kp-OXA-48-like. This is, to our knowledge, the first study to describe in K. pneumoniae producing plasmid-encoded carbapenemase, the potential impact of Hg in the co-transfer of mer operons and carbapenemase genes located in the same or different plasmids. KEY POINTS: • Environmental reservoirs are playing an important role in the selection of carbapenemase genes. • Conjugation assays, selecting with Hg, obtained 10 transconjugants with carbapenemase genes. • mer operons were located in the same or different plasmids than carbapenemase genes.

Lipid engineered nanoparticle therapy for burn wound treatment

INTRODUCTION

Skin is the largest organ of the human body protecting the underlying organs and tissues from any foreign attack. Any damage caused in the skin may sometimes result in serious consequences within the internal body tissues. Burn is one such issue that damage the layers of skin and thereby makingthe skin vulnerableand pronefor any foreign matter to enter and cause serious diseases.

METHODS

An online literature assessment was steered for the lipid nanoparticles, burn wound treatments, and different types of nanoformulation. Appropriate information was taken from different electronic scientific databases such as Web of Science, Elsevier, Science Direct, Springer, PubMed, Google Scholar etc.,Additional data was summarized from textbooks, local prints and scripts.

RESULTS

Recent innovations and developments in nanotechnology-based drug delivery systems has shown promising results in minimizing the drawbacks associated with conventional therapies. Lipid based nanoparticles possess capabilities to deliver active agents to their target site without the possibility of degradation. Conventional therapy of burn wound is costly and the treatment is long lasting, making the patient uncomfortable. Moreover, italso doesn't yield satisfactory results or narrow effects.Encapsulation of bioactives inside the lipid core protects the active entity from pH and enzymatic degradations.

CONCLUSION

This review highlights the drawbacks associated with the conventional dosage forms. A lot of consideration is focused on the advancement of nanomaterials using innovative methods in wound care for treating burn wounds with the faster healing effect.This review article highlights recent developments in lipid based nanoformulations for treatment of burn wound injury.

Two high-risk clones of carbapenemase-producing Klebsiella pneumoniae that cause infections in pets and are present in the environment of a veterinary referral hospital

OBJECTIVES

Infections with carbapenem-resistant Enterobacterales (CRE) are an emerging problem in pets and a major threat to public health. We determined the genetic relationships among carbapenemase-producing Klebsiella pneumoniae (CPKp) strains causing infections in hospitalized pets in a veterinary clinic and those found in the environment.

METHODS

WGS was performed with both the Illumina and Nanopore platforms. Searches of genetic features were performed using several databases and bioinformatics tools, and phylogeny was assessed by whole-genome MLST (wgMLST) using SeqSphere and SNP calling with Snippy.

RESULTS

WGS analysis of the CPKp strains identified all environmental and almost all animal strains as the high-risk clone ST11, with the exception of two strains that belonged to ST307. All CPKp belonged to novel complex types (CTs) and carried a conjugative 63 kb IncL plasmid encoding the carbapenemase gene blaOXA-48, yersiniabactin and other virulence factors. Although all CPKp ST11 strains carried additional similar IncR plasmids harbouring multiple antimicrobial resistance genes (ARGs), such as the plasmid-mediated blaDHA-1 AmpC gene, some structural variations were observed. The two ST307 strains carried identical 156 kb MDR IncFIB(K) plasmids with several ARGs, including the blaCTX-M-15 ESBL gene. Both wgMLST and cgSNP analysis confirmed that CPKp strains of the same ST were genetically highly related independent of the source of isolation.

CONCLUSIONS

This study demonstrated that the clinical CPKp strains were highly related to those contaminating the clinical environment. These findings confirmed nosocomial spread and highlight veterinary hospitals as a source of CPKp, which may further spread to animals, the environment and humans.

Clinically isolated bacteria resistance to silver-based wound dressings

OBJECTIVE

Silver has become a global treatment option with the US Food and Drug Administration providing marketing clearance for many silver-impregnated wound dressings and topical agents. However, the increased use of silver-based products across medical disciplines has raised questions concerning the development of acute silver resistance. In this study, the efficacy of previously identified silver-resistant clinical bacteria (Klebsiella pneumoniae and Enterobacter cloacae) against a variety of commercially available silver-based wound dressings was further investigated.

METHOD

To further explore the clinical significance of these isolates, multiple time-course and repeat-challenge assays were conducted with nine dressings using a panel of silver-resistant and silver-sensitive microorganisms. Silver-impregnated dressings were ranked by silver species, quantity of silver and overall efficacy.

RESULTS

Both silver-resistant strains were largely unaffected and exhibited phenotypic resistance even when exposed to the high silver concentrations found in commercially available wound dressings. In stark contrast, the majority of the dressings were able to maintain a high degree of efficacy over the course of 72 hours and during repeated bacterial challenges against silver-sensitive microorganisms.

CONCLUSION

Our findings provide additional evidence that clinically significant silver-resistance has emerged in the clinical setting. Such resistant microbes are capable of sustained silver resistance against a wide variety of silver adjuvants. These findings suggest that the further development and dissemination of these resistance mechanisms could significantly impact current practices in wound healing.

Update on the role of antiseptics in the management of chronic wounds with critical colonisation and/or biofilm

Biofilms play a major role in delaying chronic wounds from healing. A wound infiltrated with biofilm, or "critically colonised" wound, may become clinically infected if the number of microbes exceeds a critical level. Chronic wound biofilms represent a significant treatment challenge by demonstrating recalcitrance towards antimicrobial agents. However, a "window of opportunity" may exist after wound debridement when biofilms are more susceptible to topical antiseptics. Here, we discuss the role of antiseptics in the management of chronic wounds and biofilm, focusing on povidone-iodine (PVP-I) in comparison with two commonly used antiseptics: polyhexanide (PHMB) and silver. This article is based on the literature reviewed during a focus group meeting on antiseptics in wound care and biofilm management, and on a PubMed search conducted in March 2020. Compared with PHMB and silver, PVP-I has a broader spectrum of antimicrobial activity, potent antibiofilm efficacy, no acquired bacterial resistance or cross-resistance, low cytotoxicity, good tolerability, and an ability to promote wound healing. PVP-I represents a viable therapeutic option in wound care and biofilm management, with the potential to treat biofilm-infiltrated, critically colonised wounds. We propose a practical algorithm to guide the management of chronic, non-healing wounds due to critical colonisation or biofilm, using PVP-I.

Nanoparticles as therapeutic options for treating multidrug-resistant bacteria: research progress, challenges, and prospects

Resistance to antimicrobial agents has been alarming in recent years and poses a huge public health threat globally according to the WHO. The increase in morbidity and mortality resulting from microbial infections has been attributed to the emergence of multidrug-resistant microbes. Associated with the increase in multidrug resistance is the lack of new and effective antimicrobials. This has led to global initiatives to identify novel and more effective antimicrobial agents in addition to discovering novel and effective drug delivery and targeting methods. The use of nanoparticles as novel biomaterials to fully achieve this feat is currently gaining global attention. Nanoparticles could become an indispensable viable therapeutic option for treating drug-resistant infections. Of all the nanoparticles, the metals and metal oxide nanoparticles appear to offer the most promise and have attracted tremendous interest from many researchers. Moreover, the use of nanomaterials in photothermal therapy has received considerable attention over the years. This review provides current insight on antimicrobial resistance as well as the mechanisms of nanoparticle antibacterial activity. It offers an in-depth review of all the recent findings in the use of nanomaterials as agents against multi-resistant pathogenic bacteria. Also, nanomaterials that can respond to light stimuli (photothermal therapy) to kill microbes and facilitate enhanced drug delivery and release are discussed. Moreover, the synergistic interactions of nanoparticles with antibiotics and other nanomaterials, microbial adaptation strategies to nanoparticles, current challenges, and future prospects were extensively discussed.

Nanoparticles as therapeutic options for treating multidrug-resistant bacteria: research progress, challenges, and prospects

Resistance to antimicrobial agents has been alarming in recent years and poses a huge public health threat globally according to the WHO. The increase in morbidity and mortality resulting from microbial infections has been attributed to the emergence of multidrug-resistant microbes. Associated with the increase in multidrug resistance is the lack of new and effective antimicrobials. This has led to global initiatives to identify novel and more effective antimicrobial agents in addition to discovering novel and effective drug delivery and targeting methods. The use of nanoparticles as novel biomaterials to fully achieve this feat is currently gaining global attention. Nanoparticles could become an indispensable viable therapeutic option for treating drug-resistant infections. Of all the nanoparticles, the metals and metal oxide nanoparticles appear to offer the most promise and have attracted tremendous interest from many researchers. Moreover, the use of nanomaterials in photothermal therapy has received considerable attention over the years. This review provides current insight on antimicrobial resistance as well as the mechanisms of nanoparticle antibacterial activity. It offers an in-depth review of all the recent findings in the use of nanomaterials as agents against multi-resistant pathogenic bacteria. Also, nanomaterials that can respond to light stimuli (photothermal therapy) to kill microbes and facilitate enhanced drug delivery and release are discussed. Moreover, the synergistic interactions of nanoparticles with antibiotics and other nanomaterials, microbial adaptation strategies to nanoparticles, current challenges, and future prospects were extensively discussed.

Antimicrobial properties of nanoparticles in the context of advantages and potential risks of their use

The popularity of nanotechnology results from the possibility of obtaining materials that have better chemical, electrical, thermal, mechanical, or optical properties. Nano-sized materials are characterized by an increased surface area, which improves their chemical reactivity and mobility. Due to their enhanced reactivity and appropriately small size, some nanoparticles are used as antimicrobial and antifungal agents. Nanoparticles exhibit antimicrobial potential through multifaceted mechanisms. The adhesion of nanoparticles to microbial cells, and reactive oxygen species, and their penetration inside the cells, have been recognized as the most prominent modes of antimicrobial action. This review presents the mechanism of action of nanometals and oxide nanoparticles used as antimicrobials and the mechanisms of bacterial resistance to the toxic effects of nanoparticles. The article presents methods of forming microorganism resistance to the toxic effects of nanoparticles and the negative impact of nanoparticles on human health.

Emerging Concern for Silver Nanoparticle Resistance in Acinetobacter baumannii and Other Bacteria

The misuse of antibiotics combined with a lack of newly developed ones is the main contributors to the current antibiotic resistance crisis. There is a dire need for new and alternative antibacterial options and nanotechnology could be a solution. Metal-based nanoparticles, particularly silver nanoparticles (NAg), have garnered widespread popularity due to their unique physicochemical properties and broad-spectrum antibacterial activity. Consequently, NAg has seen extensive incorporation in many types of products across the healthcare and consumer market. Despite clear evidence of the strong antibacterial efficacy of NAg, studies have raised concerns over the development of silver-resistant bacteria. Resistance to cationic silver (Ag+) has been recognised for many years, but it has recently been found that bacterial resistance to NAg is also possible. It is also understood that exposure of bacteria to toxic heavy metals like silver can induce the emergence of antibiotic resistance through the process of co-selection. Acinetobacter baumannii is a Gram-negative coccobacillus and opportunistic nosocomial bacterial pathogen. It was recently listed as the "number one" critical level priority pathogen because of the significant rise of antibiotic resistance in this species. NAg has proven bactericidal activity towards A. baumannii, even against strains that display multi-drug resistance. However, despite ample evidence of heavy metal (including silver; Ag+) resistance in this bacterium, combined with reports of heavy metal-driven co-selection of antibiotic resistance, little research has been dedicated to assessing the potential for NAg resistance development in A. baumannii. This is worrisome, as the increasingly indiscriminate use of NAg could promote the development of silver resistance in this species, like what has occurred with antibiotics.

Resistance and Adaptation of Bacteria to Non-Antibiotic Antibacterial Agents: Physical Stressors, Nanoparticles, and Bacteriophages

Antimicrobial resistance is a significant threat to human health worldwide, forcing scientists to explore non-traditional antibacterial agents to support rapid interventions and combat the emergence and spread of drug resistant bacteria. Many new antibiotic-free approaches are being developed while the old ones are being revised, resulting in creating unique solutions that arise at the interface of physics, nanotechnology, and microbiology. Specifically, physical factors (e.g., pressure, temperature, UV light) are increasingly used for industrial sterilization. Nanoparticles (unmodified or in combination with toxic compounds) are also applied to circumvent in vivo drug resistance mechanisms in bacteria. Recently, bacteriophage-based treatments are also gaining momentum due to their high bactericidal activity and specificity. Although the number of novel approaches for tackling the antimicrobial resistance crisis is snowballing, it is still unclear if any proposed solutions would provide a long-term remedy. This review aims to provide a detailed overview of how bacteria acquire resistance against these non-antibiotic factors. We also discuss innate bacterial defense systems and how bacteriophages have evolved to tackle them.

A mechanistic perspective on targeting bacterial drug resistance with nanoparticles

Bacterial infections are an important cause of mortality worldwide owing to the prevalence of drug resistant bacteria. Bacteria develop resistance against antimicrobial drugs by several mechanisms such as enzyme inactivation, reduced cell permeability, modifying target site or enzyme, enhanced efflux because of high expression of efflux pumps, biofilm formation or drug-resistance gene expression. New and alternative ways such as nanoparticle (NP) applications are being established to overcome the growing multidrug-resistance in bacteria. NPs have unique antimicrobial characteristics that make them appropriate for medical application to overcome antibiotic resistance. The proposed antibacterial mechanisms of NPs are cell membrane damage, changing cell wall penetration, reactive oxygen species (ROS) production, effect on DNA and proteins, and impact on biofilm formation. The present review mainly focuses on discussing various mechanisms of bacterial drug resistance and the applications of NPs as alternative antibacterial systems. Combination therapy of NPs and antibiotics as a novel approach in medicine towards antimicrobial resistance is also discussed.

Antimicrobial stewardship of antiseptics that are pertinent to wounds: the need for a united approach

Long before the nature of infection was recognized, or the significance of biofilms in delayed healing was understood, antimicrobial agents were being used in wound care. In the last 70 years, antibiotics have provided an effective means to control wound infection, but the continued emergence of antibiotic-resistant strains and the documented antibiotic tolerance of biofilms has reduced their effectiveness. A range of wound dressings containing an antimicrobial (antibiotic or non-antibiotic compound) has been developed. Whereas standardized methods for determining the efficacy of non-antibiotic antimicrobials in bacterial suspension tests were developed in the early twentieth century, standardized ways of evaluating the efficacy of antimicrobial dressings against microbial suspensions and biofilms are not available. Resistance to non-antibiotic antimicrobials and cross-resistance with antibiotics has been reported, but consensus on breakpoints is absent and surveillance is impossible. Antimicrobial stewardship is therefore in jeopardy. This review highlights these difficulties and in particular the efficacy of current non-antibiotic antimicrobials used in dressings, their efficacy, and the challenges of translating in vitro efficacy data to the efficacy of dressings in patients. This review calls for a unified approach to developing standardized methods of evaluating antimicrobial dressings that will provide an improved basis for practitioners to make informed choices in wound care.

Metallic Nanoparticles-Friends or Foes in the Battle against Antibiotic-Resistant Bacteria?

The rapid spread of antibiotic resistances among bacteria demands novel strategies for infection control, and metallic nanoparticles appear as promising tools because of their unique size and tunable properties that allow their antibacterial effects to be maximized. Furthermore, their diverse mechanisms of action towards multiple cell components have suggested that bacteria could not easily develop resistance against nanoparticles. However, research published over the last decade has proven that bacteria can indeed evolve stable resistance mechanisms upon continuous exposure to metallic nanoparticles. In this review, we summarize the currently known individual and collective strategies employed by bacteria to cope with metallic nanoparticles. Importantly, we also discuss the adverse side effects that bacterial exposure to nanoparticles may have on antibiotic resistance dissemination and that might constitute a challenge for the implementation of nanoparticles as antibacterial agents. Overall, studies discussed in this review point out that careful management of these very promising antimicrobials is necessary to preserve their efficacy for infection control.

The Antibacterial Drug Candidate SBC3 is a Potent Inhibitor of Bacterial Thioredoxin Reductase

Antibiotic resistance is a growing problem for public health and associated with increasing economic costs and mortality rates. Silver and silver-related compounds have been used for centuries due to their antimicrobial properties. In this work, we show that 1,3-dibenzyl-4,5-diphenyl-imidazol-2-ylidene silver(I) acetate/NHC*-Ag-OAc (SBC3) is a reversible, high affinity inhibitor of E. coli thioredoxin reductase (TrxR; K_i =10.8±1.2 nM). Minimal inhibition concentration (MIC) tests with different E. coli and P. aeruginosa strains demonstrated that SBC3 can efficiently inhibit bacterial cell growth, especially in combination with established antibiotics like gentamicin. Our results show that SBC3 is a promising antibiotic drug candidate targeting bacterial TrxR.

DNA-Binding and Transcription Activation by Unphosphorylated Response Regulator AgrR From Cupriavidus metallidurans Involved in Silver Resistance

Even though silver and silver nanoparticles at low concentrations are considered safe for human health, their steadily increasing use and associated release in nature is not without risk since it may result in the selection of silver-resistant microorganisms, thus impeding the utilization of silver as antimicrobial agent. Furthermore, increased resistance to metals may be accompanied by increased antibiotic resistance. Inactivation of the histidine kinase and concomitant upregulation of the cognate response regulator (RR) of the AgrRS two-component system was previously shown to play an important role in the increased silver resistance of laboratory adapted mutants of Cupriavidus metallidurans. However, binding of AgrR, a member of the OmpR/PhoP family of RRs with a conserved phosphoreceiver aspartate residue, to potential target promoters has never been demonstrated. Here we identify differentially expressed genes in the silver-resistant mutant NA4S in non-selective conditions by RNA-seq and demonstrate sequence-specific binding of AgrR to six selected promoter regions of upregulated genes and divergent operons. We delimit binding sites by DNase I and in gel copper-phenanthroline footprinting of AgrR-DNA complexes, and establish a high resolution base-specific contact map of AgrR-DNA interactions using premodification binding interference techniques. We identified a 16-bp core AgrR binding site (AgrR box) arranged as an imperfect inverted repeat of 6 bp (ATTACA) separated by 4 bp variable in sequence (6-4-6). AgrR interacts with two major groove segments and the intervening minor groove, all aligned on one face of the helix. Furthermore, an additional in phase imperfect direct repeat of the half-site may be observed slightly up and/or downstream of the inverted repeat at some operators. Mutant studies indicated that both inverted and direct repeats contribute to AgrR binding in vitro and AgrR-mediated activation in vivo. From the position of the AgrR box it appears that AgrR may act as a Type II activator for most investigated promoters, including positive autoregulation. Furthermore, we show in vitro binding and in vivo activation with dephosphomimetic AgrR mutant D51A, indicating that unphosphorylated AgrR is the active form of the RR in mutant NA4S.

Photothermal-assisted antibacterial application of graphene oxide-Ag nanocomposites against clinically isolated multi-drug resistant Escherichia coli

In the field of public health, treatment of multidrug-resistant (MDR) bacterial infection is a great challenge. Herein, we provide a solution to this problem with the use of graphene oxide-silver (GO-Ag) nanocomposites as antibacterial agent. Following established protocols, silver nanoparticles were grown on graphene oxide sheets. Then, a series of in vitro studies were conducted to validate the antibacterial efficiency of the GO-Ag nanocomposites against clinical MDR Escherichia coli (E. coli) strains. GO-Ag nanocomposites showed the highest antibacterial efficiency among tested antimicrobials (graphene oxide, silver nanoparticles, GO-Ag), and synergetic antibacterial effect was observed in GO-Ag nanocomposites treated group. Treatment with 14.0 µg ml-1 GO-Ag could greatly inhibit bacteria growth; remaining bacteria viabilities were 4.4% and 4.1% for MDR-1 and MDR-2 E. coli bacteria, respectively. In addition, with assistance of photothermal effect, effective sterilization could be achieved using GO-Ag nanocomposites as low as 7.0 µg ml-1. Fluorescence imaging and morphology characterization uncovered that bacteria integrity was disrupted after GO-Ag nanocomposites treatment. Cytotoxicity results of GO-Ag using human-derived cell lines (HEK 293T, Hep G2) suggested more than 80% viability remained at 7.0 µg ml-1. All the results proved that GO-Ag nanocomposites are efficient antibacterial agent against multidrug-resistant E. coli.

Risk and clinical impact of bacterial resistance/susceptibility to silver-based wound dressings: a systematic review

Objective:

To perform a systematic review of the literature on bacterial resistance, tolerance and susceptibility of silver within the context of wound therapy using silver-based dressings.

Methods:

A literature search was carried out using PubMed, Embase and Cochrane Library databases, the focus was whether results from microbiological experimental in vitro tests with reference strains and clinical wound isolates are reflected in clinical practice with regards to their ‘resistance’ profiles, comparable with those observed for antibiotics. The search results were allocated to six categories: resistance and resistance mechanism, in vitro tests with standard strains and wound isolates, prevalence and incidence, impact on clinical practice and impact on antibiotic therapy as well as reviews, expert opinions and consensus.

Results:

Based on all findings of the literature, it cannot be confirmed that a related clinical resistance to silver-ions in silver-based dressings has clinical impact, although endogenous and exogenous genetic resistance patterns have been described and intensively investigated. A translation of these genetic resistance-expression structures to phenotypic appearances, similar to those known for antibiotics, has not been demonstrated for silver in the literature.

Conclusion:

It can be concluded that there is no definitive evidence available and further studies should be conducted.

Silver Nanoparticles for the Therapy of Tuberculosis

Rapid emergence of aggressive, multidrug-resistant Mycobacteria strain represents the main cause of the current antimycobacterial-drug crisis and status of tuberculosis (TB) as a major global health problem. The relatively low-output of newly approved antibiotics contributes to the current orientation of research towards alternative antibacterial molecules such as advanced materials. Nanotechnology and nanoparticle research offers several exciting new-concepts and strategies which may prove to be valuable tools in improving the TB therapy. A new paradigm in antituberculous therapy using silver nanoparticles has the potential to overcome the medical limitations imposed in TB treatment by the drug resistance which is commonly reported for most of the current organic antibiotics. There is no doubt that AgNPs are promising future therapeutics for the medication of mycobacterial-induced diseases but the viability of this complementary strategy depends on overcoming several critical therapeutic issues as, poor delivery, variable intramacrophagic antimycobacterial efficiency, and residual toxicity. In this paper, we provide an overview of the pathology of mycobacterial-induced diseases, andhighlight the advantages and limitations of silver nanoparticles (AgNPs) in TB treatment.

Multifunctional Copper-Containing Mesoporous Glass Nanoparticles as Antibacterial and Proangiogenic Agents for Chronic Wounds

The physiological wound healing process involves a cascade of events which could be affected by several factors resulting in chronic, non-healing wounds. The latter represent a great burden especially when bacterial biofilms are formed. The rise in antibiotic resistance amongst infectious microorganisms leads to the need of novel approaches to treat this clinical issue. In this context, the use of advanced biomaterials, which can enhance the physiological expression and secretion of the growth factors involved in the wound healing process, is gaining increasing attention as a robust and appealing alternative approach. Among them, mesoporous glasses are of particular interest due to their excellent textural properties and to the possibility of incorporating and releasing specific therapeutic species, such as metallic ions. One of the most attractive therapeutic ions is copper thanks to its proangiogenic and antibacterial effects. In this contribution, copper containing mesoporous glass nanoparticles were proposed as a multifunctional device to treat chronic wounds. The developed nanoparticles evidenced a very high specific surface area (740 m²/g), uniform pores of 4 nm and an almost total release of the therapeutic ion within 72 h of soaking. The produced nanoparticles were biocompatible and, when tested against Gram positive and Gram negative bacterial species, demonstrated antibacterial activity against both planktonic and biofilm bacteria in 2D cell monolayers, and in a 3D human model of infected skin. Their proangiogenic effect was tested with both the aortic ring and the chick chorioallantoic membrane assays and an increase in endothelial cell outgrowth at a concentration range between 30 and 300 ng/mL was shown. Overall, in this study biocompatible, multifunctional Cu-containing mesoporous glass nanoparticles were successfully produced and demonstrated to exert both antibacterial and proangiogenic effects.

Silver Nanoparticles Synthesized by Using Bacillus cereus SZT1 Ameliorated the Damage of Bacterial Leaf Blight Pathogen in Rice

Amongst serious biotic factors deteriorating crop yield, the most destructive pathogen of rice is Xanthomonas oryzae pv. oryzae (Xoo), which causes bacterial leaf blight (BLB) disease. This study involved targeted use of biogenic silver nanoparticles (AgNPs) to control BLB in order to cope with the disadvantages of chemical disease control. AgNPs were biologically synthesized from natively isolated Bacillus cereus strain SZT1, which was identified through 16S rRNA gene sequence analysis. Synthesis of AgNPs in bacterial culture supernatant was confirmed through UV-VIS spectroscopy. Fourier transform infrared spectroscopy (FTIR) confirmed that the existence of AgNPs was stabilized with proteins and alcoholic groups. X-ray diffraction (XRD) data revealed the crystalline nature and imaging with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), showing the spherical shape of AgNPs with particle sizes ranging from 18 to 39 nm. The silver presence in AgNPs was further confirmed by energy dispersive spectra. Biogenic AgNPs showed substantial antibacterial activity (24.21 ± 1.01 mm) for Xoo. In a pot experiment, AgNPs were found to be effective weapons for BLB by significantly increasing the plant biomass with a decreased cellular concentration of reactive oxygen species and increased concentration of antioxidant enzyme activity.

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday 'antibacterial' products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.

Consequences Of Long-Term Bacteria's Exposure To Silver Nanoformulations With Different PhysicoChemical Properties

Purpose

Resistance to antibiotics is a major problem of public health. One of the alternative therapies is silver – more and more popular because of nanotechnology development and new possibilities of usage. As a component of colloid, powder, cream, bandages, etc., nanosilver is often recommended to treat the multidrug-resistant pathogens and we can observe its overuse also outside of the clinic where different physicochemical forms of silver nanoformulations (e.g. size, shape, compounds, surface area) are introduced. In this research, we described the consequences of long-term bacteria exposure to silver nanoformulations with different physicochemical properties, including changes in genome and changes of bacterial sensitivity to silver nanoformulations and/or antibiotics. Moreover, the prevalence of exogenous resistance to silver among multidrug-resistant bacteria was determined.

Materials and Methods

Gram-negative and Gram-positive bacteria strains are described as sensitive and multidrug-resistant strains. The sensitivity of the tested bacterial strains to antibiotics was carried out with disc diffusion methods. The sensitivity of bacteria to silver nanoformulations and development of bacterial resistance to silver nanoformulations has been verified via determination of the minimal inhibitory concentrations. The presence of sil genes was verified via PCR reaction and DNA electrophoresis. The genomic and phenotypic changes have been verified via genome sequencing and bioinformatics analysis.

Results

Bacteria after long-term exposure to silver nanoformulations may change their sensitivity to silver forms and/or antibiotics, depending on the physicochemical properties of silver nanoformulations, resulting from phenotypic or genetic changes in the bacterial cell. Finally, adaptants and mutants may become more sensitive or resistant to some antibiotics than wild types.

Conclusion

Application of silver nanoformulations in the case of multiple resistance or multidrug-resistant bacterial infection can enhance or decrease their resistance to antibiotics. The usage of nanosilver in a clinic and outside of the clinic should be determined and should be under strong control. Moreover, each silver nanomaterial should be considered as a separate agent with a potential different mode of antibacterial action.

Impacts of silver-coated antimicrobial screen covers on the cell-phone microbiome of resident physicians

An antimicrobial screen was applied to the cell phones of 26 resident physicians to determine its effects on the phone microbiome and its potential to serve as a selective agent for antibiotic or silver resistance genes. No increase of these genes was observed now was there a shift in the overall microbial community.

Nanoparticles in the Treatment of Infections Caused by Multidrug-Resistant Organisms

Nanotechnology using nanoscale materials is increasingly being utilized for clinical applications, especially as a new paradigm for infectious diseases. Infections caused by multidrug-resistant organisms (MDROs) are emerging as causes of morbidity and mortality worldwide. Antibiotic options for infections caused by MDROs are often limited. These clinical challenges highlight the critical demand for alternative and effective antimicrobial strategies. Nanoparticles (NPs) can penetrate the cell membrane of pathogenic microorganisms and interfere with important molecular pathways, formulating unique antimicrobial mechanisms. In combination with optimal antibiotics, NPs have demonstrated synergy and may aid in limiting the global crisis of emerging bacterial resistance. In this review, we summarized current research on the broad classification of the NPs that have shown in vitro antimicrobial activity against MDROs, including the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). The pharmacokinetics and pharmacodynamic characteristics of NPs and bacteria-resistant mechanisms to NPs were also discussed.