Gold Nanoclusters as an Antibacterial Alternative Against Clostridium difficile

Microscopy methods for Clostridioides difficile

Microscopic technologies including light and fluorescent, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and cryo-electron microscopy have been widely utilized to visualize Clostridioides difficile at the molecular, cellular, community, and structural biology level. This comprehensive review summarizes the microscopy tools (fluorescent and reporter system) in their use to study different aspects of C. difficile life cycle and virulence (sporulation, germination) or applications (detection of C. difficile or use of antimicrobials). With these developing techniques, microscopy tools will be able to find broader applications and address more challenging questions to study C. difficile and C. difficile infection.

Size and charge effects of metal nanoclusters on antibacterial mechanisms

Nanomaterials, specifically metal nanoclusters (NCs), are gaining attention as a promising class of antibacterial agents. Metal NCs exhibit antibacterial properties due to their ultrasmall size, extensive surface area, and well-controlled surface ligands. The antibacterial mechanisms of metal NCs are influenced by two primary factors: size and surface charge. In this review, we summarize the impacts of size and surface charge of metal NCs on the antibacterial mechanisms, their interactions with bacteria, and the factors that influence their antibacterial effects against both gram-negative and gram-positive bacteria. Additionally, we highlight the mechanisms that occur when NCs are negatively or positively charged, and provide examples of their applications as antibacterial agents. A better understanding of relationships between antibacterial activity and the properties of metal NCs will aid in the design and synthesis of nanomaterials for the development of effective antibacterial agents against bacterial infections. Based on the remarkable achievements in the design of metal NCs, this review also presents conclusions on current challenges and future perspectives of metal NCs for both fundamental investigations and practical antibacterial applications.

Phenylboronic Acid-Modified Gold Nanoclusters as a Nanoantibiotic to Treat Vancomycin-Resistant Enterococcus faecalis-Caused Infections

Vancomycin is one of the last lines of defense against certain drug-resistant bacteria-caused infections. However, the high susceptibility to drug resistance and high toxicity seriously limit the application of vancomycin. Nanoantibiotics provide opportunities to solve these problems. Herein, we present mercaptophenylboronic acid (MBA)-modified gold nanoclusters with well-defined molecular formulas and structure (Au44(MBA)18) and excellent antibacterial activities against various drug-resistant bacteria such as vancomycin-resistant Enterococcus faecalis (VRE). Au44(MBA)18 interacts with bacteria by first attaching to teichoic-acid and destroying the cell wall and subsequently binding to the bacterial DNA. Au44(MBA)18 could be administered via multiple routes and has a high biosafety (500 mg/kg, no ototoxicity), overcoming the two major shortcomings of vancomycin (sole administration route and high ototoxicity). Our study is insightful for curing infections caused by multidrug-resistant bacteria using nanoantibiotics with high biosafety.

Host Immunity and Immunization Strategies for Clostridioides difficile Infection

Clostridioides difficile infection (CDI) represents a significant challenge to public health. C. difficile-associated mortality and morbidity have led the U.S. CDC to designate it as an urgent threat. Moreover, recurrence or relapses can occur in up to a third of CDI patients, due in part to antibiotics being the primary treatment for CDI and the major cause of the disease. In this review, we summarize the current knowledge of innate immune responses, adaptive immune responses, and the link between innate and adaptive immune responses of the host against CDI. The other major determinants of CDI, such as C. difficile toxins, the host microbiota, and related treatments, are also described. Finally, we discuss the known therapeutic approaches and the current status of immunization strategies for CDI, which might help to bridge the knowledge gap in the generation of therapy against CDI.

Gold-Based Nanostructures for Antibacterial Application

Bacterial infections have become a fatal threat because of the abuse of antibiotics in the world. Various gold (Au)-based nanostructures have been extensively explored as antibacterial agents to combat bacterial infections based on their remarkable chemical and physical characteristics. Many Au-based nanostructures have been designed and their antibacterial activities and mechanisms have been further examined and demonstrated. In this review, we collected and summarized current developments of antibacterial agents of Au-based nanostructures, including Au nanoparticles (AuNPs), Au nanoclusters (AuNCs), Au nanorods (AuNRs), Au nanobipyramids (AuNBPs), and Au nanostars (AuNSs) according to their shapes, sizes, and surface modifications. The rational designs and antibacterial mechanisms of these Au-based nanostructures are further discussed. With the developments of Au-based nanostructures as novel antibacterial agents, we also provide perspectives, challenges, and opportunities for future practical clinical applications.

Mining chicken ileal microbiota for immunomodulatory microorganisms

The gut microbiota makes important contributions to host immune system development and resistance to pathogen infections, especially during early life. However, studies addressing the immunomodulatory functions of gut microbial individuals or populations are limited. In this study, we explore the systemic impact of the ileal microbiota on immune cell development and function of chickens and identify the members of the microbiota involved in immune system modulation. We initially used a time-series design with six time points to prove that ileal microbiota at different succession stages is intimately connected to immune cell maturation. Antibiotics perturbed the microbiota succession and negatively affected immune development, whereas early exposure to the ileal commensal microbiota from more mature birds promoted immune cell development and facilitated pathogen elimination after Salmonella Typhimurium infection, illustrating that early colonization of gut microbiota is an important driver of immune development. Five bacterial strains, Blautia coccoides, Bacteroides xylanisolvens, Fournierella sp002159185, Romboutsia lituseburensis, and Megamonas funiformis, which are closely related to the immune system development of broiler chickens, were then screened out and validated for their immunomodulatory properties. Our results provide insight into poultry immune system-microbiota interactions and also establish a foundation for targeted immunological interventions aiming to combat infectious diseases and promote poultry health and production.

Antibacterial metal nanoclusters

Combating bacterial infections is one of the most important applications of nanomedicine. In the past two decades, significant efforts have been committed to tune physicochemical properties of nanomaterials for the development of various novel nanoantibiotics. Among which, metal nanoclusters (NCs) with well-defined ultrasmall size and adjustable surface chemistry are emerging as the next-generation high performance nanoantibiotics. Metal NCs can penetrate bacterial cell envelope more easily than conventional nanomaterials due to their ultrasmall size. Meanwhile, the abundant active sites of the metal NCs help to catalyze the bacterial intracellular biochemical processes, resulting in enhanced antibacterial properties. In this review, we discuss the recent developments in metal NCs as a new generation of antimicrobial agents. Based on a brief introduction to the characteristics of metal NCs, we highlight the general working mechanisms by which metal NCs combating the bacterial infections. We also emphasize central roles of core size, element composition, oxidation state, and surface chemistry of metal NCs in their antimicrobial efficacy. Finally, we present a perspective on the remaining challenges and future developments of metal NCs for antibacterial therapeutics.

rRNA Analysis Based on Long-Read High-Throughput Sequencing Reveals a More Accurate Diagnostic for the Bacterial Infection of Ascites

Traditional pathogenic diagnosis presents defects such as a low positivity rate, inability to identify uncultured microorganisms, and time-consuming nature. Clinical metagenomics next-generation sequencing can be used to detect any pathogen, compensating for the shortcomings of traditional pathogenic diagnosis. We report third-generation long-read sequencing results and second-generation short-read sequencing results for ascitic fluid from a patient with liver ascites and compared the two types of sequencing results with the results of traditional clinical microbial culture. The distribution of pathogenic microbial species revealed by the two types of sequencing results was quite different, and the third-generation sequencing results were consistent with the results of traditional microbial culture, which can effectively guide subsequent treatment. Short reads, the lack of amplification, and enrichment to amplify signals from trace pathogens, and host background noise may be the reasons for the high error in the second-generation short-read sequencing results. Therefore, we propose that long-read-based rRNA analysis technology is superior to the short-read shotgun-based metagenomics method in the identification of pathogenic bacteria.

High Stability Au NPs: From Design to Application in Nanomedicine

In recent years, Au-based nanomaterials are widely used in nanomedicine and biosensors due to their excellent physical and chemical properties. However, these applications require Au NPs to have excellent stability in different environments, such as extreme pH, high temperature, high concentration ions, and various biomatrix. To meet the requirement of multiple applications, many synthetic substances and natural products are used to prepare highly stable Au NPs. Because of this, we aim at offering an update comprehensive summary of preparation high stability Au NPs. In addition, we discuss its application in nanomedicine. The contents of this review are based on a balanced combination of our studies and selected research studies done by worldwide academic groups. First, we address some critical methods for preparing highly stable Au NPs using polymers, including heterocyclic substances, polyethylene glycols, amines, and thiol, then pay attention to natural product progress Au NPs. Then, we sum up the stability of various Au NPs in different stored times, ions solution, pH, temperature, and biomatrix. Finally, the application of Au NPs in nanomedicine, such as drug delivery, bioimaging, photothermal therapy (PTT), clinical diagnosis, nanozyme, and radiotherapy (RT), was addressed concentratedly.

Au Nanoclusters Ameliorate Shigella Infectious Colitis by Inducing Oxidative Stress

Background

Shigella infection has always been a global burden, and it particularly threatens children between the ages of 1 and 5 years. Economically underdeveloped countries are dominated by Shigella flexneri infection. The most effective method to treat Shigella is antibiotics, but with the abuse of antibiotics and the prevalence of multidrug resistance, we urgently need a relatively safe non-antibiotic treatment to replace it. Ultrasmall Au nanoclusters (NCs) have special physical and chemical properties and can better interact with and be internalized by bacteria to disrupt the metabolic balance. The purpose of this study was to explore whether Au NCs may be a substitute for antibiotics to treat Shigella infections.

Methods

Au NCs and Shigella Sf301, R2448, and RII-1 were cocultured in vitro to evaluate the bactericidal ability of Au NCs. The degree of damage and mode of action of Au NCs in Shigella were clearly observed in images of scanning electron microscopy (SEM). In vivo experiments were conducted to observe the changes in body weight, clinical disease activity index (DAI) and colon (including length and histopathological sections) of mice treated with Au NCs. The effect of Au NCs was analysed by measuring the content of lipocalin-2 (LCN2) and Shigella in faeces. Next, the changes in Shigella biofilm activity, the release of reactive oxygen species (ROS), the changes in metabolism-related and membrane-related genes, and the effect of Au NCs on the body weight of mice were determined to further analyse the mechanism of action and effect.

Results

Au NCs (100 μM) interfered with oxidative metabolism genes, induced a substantial increase in ROS levels, interacted with the cell membrane to destroy it, significantly killed Shigella, and effectively alleviated the intestinal damage caused by Shigella in mice. The activity of the biofilm formed by Shigella was reduced.

Conclusion

The effective antibacterial effect and good safety suggest that Au NCs represent a good potential alternative to antibiotics to treat Shigella infections.

Overcoming bacterial physical defenses with molecule-like ultrasmall antimicrobial gold nanoclusters

The size of metal nanoparticles (NPs) is crucial in their biomedical applications. Although abundant studies on the size effects of metal NPs in the range of 2-100 nm have been conducted, the exploration of the ultrasmall metal nanoclusters (NCs) of ~1 nm in size with unique features is quite limited. We synthesize three different sized gold (Au) NCs of different Au atom numbers and two bigger sized Au NPs protected by the same ligand to study the size influence on antimicrobial efficacy. The ultrasmall Au NCs can easily traverse the cell wall pores to be internalized inside bacteria, inducing reactive oxygen species generation to oxidize bacterial membrane and disturb bacterial metabolism. This explains why the Au NCs are antimicrobial while the Au NPs are non-antimicrobial, suggesting the key role of size in antimicrobial ability. Moreover, in contrast to the widely known size-dependent antimicrobial properties, the Au NCs of different atom numbers demonstrate molecule-like instead of size-dependent antimicrobial behavior with comparable effectiveness, indicating the unique molecule-like feature of ultrasmall Au NCs. Overcoming the bacterial defenses at the wall with ultrasmall Au NCs changes what was previously believed to harmless to the bacteria instead to a highly potent agent against the bacteria.