Alternatives to Conventional Antibiotics in the Era of Antimicrobial Resistance

Amino Acid-Conjugated Polymer-Silver Bromide Nanocomposites for Eradicating Polymicrobial Biofilms and Treating Burn Wound Infections

The rise in antimicrobial resistance, the increasing occurrence of bacterial, and fungal infections, and the challenges posed by polymicrobial biofilms necessitate the exploration of innovative therapeutic strategies. Silver-based antimicrobials have garnered attention for their broad-spectrum activity and multimodal mechanisms of action. However, their effectiveness against single-species or polymicrobial biofilms remains limited. In this study, we present the fabrication of polymer-silver bromide nanocomposites using amino acid conjugated polymers (ACPs) through a green and water-based in situ technique. The nanocomposite architecture facilitated prolonged and controlled release of the active components. Remarkably, the nanocomposites exhibited broad-spectrum activity against multidrug-resistant (MDR) human pathogenic bacteria (MIC = 2-16 μg/mL) and fungi (MIC = 1-8 μg/mL), while displaying no detectable toxicity to human erythrocytes (HC50 > 1024 μg/mL). In contrast to existing antimicrobials and silver-based therapies, the nanocomposite effectively eradicated bacterial, fungal, and polymicrobial biofilms, and prevented the development of microbial resistance due to their membrane-active properties. Furthermore, the lead polymer-silver bromide nanocomposite demonstrated a 99% reduction in the drug-resistant Pseudomonas aeruginosa burden in a murine model of burn wound infection, along with excellent in vivo biocompatibility.

Nanozybiotics: Advancing Antimicrobial Strategies Through Biomimetic Mechanisms

Infectious diseases caused by bacterial, viral, and fungal pathogens present significant global health challenges. The rapid emergence of antimicrobial resistance exacerbates this issue, leading to a scenario where effective antibiotics are increasingly scarce. Traditional antibiotic development strategies are proving inadequate against the swift evolution of microbial resistance. Therefore, there is an urgent need to develop novel antimicrobial strategies with mechanisms distinct from those of existing antibiotics. Nanozybiotics, which are nanozyme-based antimicrobials, mimic the catalytic action of lysosomal enzymes in innate immune cells to kill infectious pathogens. This review reinforces the concept of nanozymes and provides a comprehensive summary of recent research advancements on potential antimicrobial candidates. Initially, nanozybiotics are categorized based on their activities, mimicking either oxidoreductase-like or hydrolase-like functions, thereby highlighting their superior mechanisms in combating antimicrobial resistance. The review then discusses the progress of nanozybiotics in treating bacterial, viral, and fungal infections, confirming their potential as novel antimicrobial candidates. The translational potential of nanozybiotic-based products, including hydrogels, nanorobots, sprays, bandages, masks, and protective clothing, is also considered. Finally, the current challenges and future prospects of nanozybiotic-related products are explored, emphasizing the design and antimicrobial capabilities of nanozybiotics for future applications.

AI-guided few-shot inverse design of HDP-mimicking polymers against drug-resistant bacteria

Host defense peptide (HDP)-mimicking polymers are promising therapeutic alternatives to antibiotics and have large-scale untapped potential. Artificial intelligence (AI) exhibits promising performance on large-scale chemical-content design, however, existing AI methods face difficulties on scarcity data in each family of HDP-mimicking polymers (<102), much smaller than public polymer datasets (>105), and multi-constraints on properties and structures when exploring high-dimensional polymer space. Herein, we develop a universal AI-guided few-shot inverse design framework by designing multi-modal representations to enrich polymer information for predictions and creating a graph grammar distillation for chemical space restriction to improve the efficiency of multi-constrained polymer generation with reinforcement learning. Exampled with HDP-mimicking β-amino acid polymers, we successfully simulate predictions of over 105 polymers and identify 83 optimal polymers. Furthermore, we synthesize an optimal polymer DM0.8iPen0.2 and find that this polymer exhibits broad-spectrum and potent antibacterial activity against multiple clinically isolated antibiotic-resistant pathogens, validating the effectiveness of AI-guided design strategy.

Nutritional Modulation of Host Defense Peptide Synthesis: A Novel Host-Directed Antimicrobial Therapeutic Strategy?

The escalating threat of antimicrobial resistance underscores the imperative for innovative therapeutic strategies. Host defense peptides (HDPs), integral components of innate immunity, exhibit profound antimicrobial and immunomodulatory properties. Various dietary compounds, such as short-chain fatty acids, vitamins, minerals, sugars, amino acids, phytochemicals, bile acids, probiotics, and prebiotics have been identified to enhance the synthesis of endogenous HDPs without provoking inflammatory response or compromising barrier integrity. Additionally, different classes of these compounds synergize in augmenting HDP synthesis and disease resistance. Moreover, dietary supplementation of several HDP-inducing compounds or their combinations have demonstrated robust protection in animals from experimental infections. However, the efficacy of these compounds in inducing HDP synthesis varies considerably among distinct compounds. Additionally, the regulation of HDP genes occurs in a gene-specific, cell type-specific, and species-specific manner. In this comprehensive review, we systematically summarized the modulation of HDP synthesis and the mechanism of action attributed to each major class of dietary compounds, including their synergistic combinations, across a spectrum of animal species including humans. We argue that the ability to enhance innate immunity and barrier function without triggering inflammation or microbial resistance positions the nutritional modulation of endogenous HDP synthesis as a promising host-directed approach for mitigating infectious diseases and antimicrobial resistance. These HDP-inducing compounds, particularly in combinations, harbor substantial clinical potential for further exploration in antimicrobial therapies for both human and other animals.

Self-assembling short peptide amphiphiles as versatile delivery agents: a new frontier in antibacterial research

Self-assembling short peptide amphiphiles, crafted through a minimalistic approach, spontaneously generate well-ordered nanostructures, facilitating the creation of precise nanostructured biomaterials for diverse biomedical applications. The seamless integration of bioactive metal ions and nanoparticles endows them with the potential to serve as pioneering materials in combating bacterial infections. Nanomanipulation of these molecules' binary structures enables effective penetration of membranes, forming structured nanoarchitectures with antibacterial properties. Through a comprehensive exploration, we attempt to reveal the innovative potential of short peptide amphiphiles, particularly in conjugation with metal cations and nanoparticles, offering insights for future research trajectories.

Antimicrobial Activity of Water-Soluble Silver Complexes Bearing C-Scorpionate Ligands

The novel hydrosoluble silver coordination polymer [Ag(NO3)(μ-1κN;2κN',N″-TPMOH)]n (1) (TPMOH = tris(1H-pyrazol-1-yl)ethanol) was obtained and characterized. While single crystal X-ray diffraction analysis of compound 1 disclosed an infinite 1D helical chain structure in the solid state, NMR analysis in polar solvents confirmed the mononuclear nature of compound 1 in solution. Compound 1 and the analogue [Ag(μ-1κN;2κN',N″-TPMS)]n (2) (TPMS = tris(1H-pyrazol-1-yl)methane sulfonate) were evaluated with regard to their antimicrobial activities towards the Gram-negative Escherichia coli, Pseudomonas aeruginosa, and Burkholderia contaminans, the Gram-positive Staphylococcus aureus, and the fungal species Candida albicans and Candida glabrata. Compound 1 exhibited minimal inhibitory concentration (MIC) values ranging from 2 to 7.7 µg/mL towards the tested Gram-negative bacteria, 18 µg/mL towards the Gram-positive S. aureus, and 15 and 31 µg/mL towards C. albicans and C. glabrata, respectively. Compound 2 was less effective towards the tested bacteria, with MIC values ranging from 15 to 19.6 µg/mL towards the Gram-negative bacteria and 51 µg/mL towards S. aureus; however, it was more effective against C. albicans and C. glabrata, with MIC values of about 6 µg/mL towards these fungal species. The toxicity of compounds 1 and 2 was assessed by evaluating the survival of the Caenorhabditis elegans model organism to concentrations of up to 100 µg/mL. The value of 50% lethality (LD50) could only be estimated as 73.2 µg/mL for compound 1 at 72 h, otherwise LD50 was >100 µg/mL for both compounds 1 and 2. These results indicate compounds 1 and 2 as novel silver complexes with interesting antimicrobial properties towards bacterial and fungal pathogens.

Recent advances in gene-editing approaches for tackling antibiotic resistance threats: a review

Antibiotic resistance, a known global health challenge, involves the flow of bacteria and their genes among animals, humans, and their surrounding environment. It occurs when bacteria evolve and become less responsive to the drugs designated to kill them, making infections harder to treat. Despite several obstacles preventing the spread of genes and bacteria, pathogens regularly acquire novel resistance factors from other species, which reduces their ability to prevent and treat such bacterial infections. This issue requires coordinated efforts in healthcare, research, and public awareness to address its impact on human health worldwide. This review outlines how recent advances in gene editing technology, especially CRISPR/Cas9, unveil a breakthrough in combating antibiotic resistance. Our focus will remain on the relationship between CRISPR/cas9 and its impact on antibiotic resistance and its related infections. Moreover, the prospects of this new advanced research and the challenges of adopting these technologies against infections will be outlined by exploring its different derivatives and discussing their advantages and limitations over others, thereby providing a corresponding reference for the control and prevention of the spread of antibiotic resistance.

Bacterial cell death to overcome drug resistance with multitargeting bis-naphthalimides as potent antibacterial agents against Enterococcus faecalis

The increasing frequency of drug-resistant pathogens poses serious health issues to humans around the globe, leading to the development of new antibacterial agents to conquer drug resistance and bacterial infections. In view of this, we have synthesized a series of bis-naphthalimides to respond to awful drug resistance. Bioactivity assay and structure-activity relationship disclosed that compounds 5d and 5o exhibit potent antibacterial activity against E. faecalis, outperforming the marketed antibiotics. These drug candidates not only inhibit the biofilm formation of E. faecalis but also display rapid bactericidal properties, thus delaying the development of drug resistance within 20 passages. To explore the mechanism of antibacterial activity against E. faecalis, biofunctional examination was carried out which unveiled that 5d and 5o effectively disrupt bacterial cell membranes, causing the leakage of cytoplasmic contents and metabolic activity loss. Concurrently, 5d and 5o effectively intercalate with DNA to block DNA replication, causing the build-up of excessive reactive oxygen species and inhibiting the glutathione activity, ultimately leading to oxidative damage of E. faecalis and cell death. In addition, these compounds readily bind with HSA with a high binding constant, indicating that these drug candidates could be easily delivered to the target site. The above finding manifested that these newly synthesized bis-naphthalimides with multitargeting antibacterial properties offer a new prospect to overcome drug resistance.

Polyoxometalate-Polymer Directed Macromolecular Architectonics of Silver Nanoparticles as Effective Antimicrobials

A novel inorganic-organic-inorganic ternary bioactive material formulated on antimicrobial peptide-based polymer has been reported. Supramolecular approach has been employed to incorporate molecularly crowded tyrosine-based polymer stabilized silver nanoparticles into membrane bound vesicles exploiting polyoxometalate-triggered surface templating strategy. Utilizing the covalent reversible addition fragmentation chain transfer (RAFT) polymerization and exploiting templated supramolecular architectonics at biopolymer interface, the bioactive ternary polymeric nanohybrids have been designed against Shigellosis leveraging the antibacterial activities of silver nanoparticle, cationic amphiphilic tyrosine polymer and inorganic polyoxometalate. The detail investigation against Shigella flexneri 2a cell line demonstrates that the collaborative mechanism of the ternary hybrid composite enhances the bactericidal activity in comparison to only polyoxometalate and polymer stabilized silver nanoparticle with an altered mechanism of action which is established via detailed biological analysis.

Toxin-triggered liposomes for the controlled release of antibiotics to treat infections associated with the gram-negative bacterium, Aggregatibacter actinomycetemcomitans

Antibiotic resistance has become an urgent threat to health care in recent years. The use of drug delivery systems provides advantages over conventional administration of antibiotics and can slow the development of antibiotic resistance. In the current study, we developed a toxin-triggered liposomal antibiotic delivery system, in which the drug release is enabled by the leukotoxin (LtxA) produced by the Gram-negative pathogen, Aggregatibacter actinomycetemcomitans. LtxA has previously been shown to mediate membrane disruption by promoting a lipid phase change in nonlamellar lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-methyl (N-methyl-DOPE). In addition, LtxA has been observed to bind strongly and nearly irreversibly to membranes containing large amounts of cholesterol. Here, we designed a liposomal delivery system composed of N-methyl-DOPE and cholesterol to take advantage of these interactions. Specifically, we hypothesized that liposomes composed of N-methyl-DOPE and cholesterol, encapsulating antibiotics, would be sensitive to LtxA, enabling controlled antibiotic release. We observed that liposomes composed of N-methyl-DOPE were sensitive to the presence of low concentrations of LtxA, and cholesterol increased the extent and kinetics of content release. The liposomes were stable under various storage conditions for at least 7 days. Finally, we showed that antibiotic release occurs selectively in the presence of an LtxA-producing strain of A. actinomycetemcomitans but not in the presence of a non-LtxA-expressing strain. Together, these results demonstrate that the designed liposomal vehicle enables toxin-triggered delivery of antibiotics to LtxA-producing strains of A. actinomycetemcomitans.

Fluoropyrimidines affect de novo pyrimidine synthesis impairing biofilm formation in Escherichia coli

Antivirulence agents are considered a promising strategy to treat bacterial infections. Fluoropyrimidines possess antivirulence and antibiofilm activity against Gram-negative bacteria; however, their mechanism of action is yet unknown. Consistent with their known antibiofilm activity, fluoropyrimidines, particularly 5-fluorocytosine (5-FC), impair curli-dependent surface adhesion by Escherichia coli MG1655 via downregulation of curli fimbriae gene transcription. Curli inhibition requires fluoropyrimidine conversion into fluoronucleotides and is not mediated by c-di-GMP or the ymg-rcs envelope stress response axis, previously suggested as the target of fluorouracil antibiofilm activity in E. coli. In contrast, 5-FC hampered the transcription of curli activators RpoS and stimulated the expression of Fis, a curli repressor affected by nucleotide availability. This last observation suggested a possible perturbation of the de novo pyrimidine biosynthesis by 5-FC: indeed, exposure to 5-FC resulted in a ca. 2-fold reduction of UMP intracellular levels while not affecting ATP. Consistently, expression of the de novo pyrimidine biosynthesis genes carB and pyrB was upregulated in the presence of 5-FC. Our results suggest that the antibiofilm activity of fluoropyrimidines is mediated, at least in part, by perturbation of the pyrimidine nucleotide pool. We screened a genome library in search of additional determinants able to counteract the effects of 5-FC. We found that a DNA fragment encoding the unknown protein D8B36_18,480 and the N-terminal domain of the penicillin-binding protein 1b (PBP1b), involved in peptidoglycan synthesis, could restore curli production in the presence of 5-FC. Deletion of the PBP1b-encoding gene mrcB, induced csgBAC transcription, while overexpression of the gene encoding the D8B36_18,480 protein obliterated its expression, possibly as part of a coordinated response in curli regulation with PBP1b. While the two proteins do not appear to be direct targets of 5-FC, their involvement in curli regulation suggests a connection between peptidoglycan biosynthesis and curli production, which might become even more relevant upon pyrimidine starvation and reduced availability of UDP-sugars needed in cell wall biosynthesis. Overall, our findings link the antibiofilm activity of fluoropyrimidines to the redirection of at least two global regulators (RpoS, Fis) by induction of pyrimidine starvation. This highlights the importance of the de novo pyrimidines biosynthesis pathway in controlling virulence mechanisms in different bacteria and makes the pathway a potential target for antivirulence strategies.

Prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections

Osteomyelitis is a devastating disease caused by microbial infection in deep bone tissue. Its high recurrence rate and impaired restoration of bone deficiencies are major challenges in treatment. Microbes have evolved numerous mechanisms to effectively evade host intrinsic and adaptive immune attacks to persistently localize in the host, such as drug-resistant bacteria, biofilms, persister cells, intracellular bacteria, and small colony variants (SCVs). Moreover, microbial-mediated dysregulation of the bone immune microenvironment impedes the bone regeneration process, leading to impaired bone defect repair. Despite advances in surgical strategies and drug applications for the treatment of bone infections within the last decade, challenges remain in clinical management. The development and application of tissue engineering materials have provided new strategies for the treatment of bone infections, but a comprehensive review of their research progress is lacking. This review discusses the critical pathogenic mechanisms of microbes in the skeletal system and their immunomodulatory effects on bone regeneration, and highlights the prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections. It will inform the development and translation of antimicrobial and bone repair tissue engineering materials for the management of bone infections.

Based on CiteSpace Insights into Illicium verum Hook. f. Current Hotspots and Emerging Trends and China Resources Distribution

Illicium verum Hook. f. is a globally significant spice, which is recognized in China as a food-medicine homolog and extensively utilized across the pharmaceutical, food, and spice industries. China boasts the world's leading resources of I. verum, yet its comprehensive utilization remains relatively underexplored. Through a resource survey of I. verum and the application of bibliometric visualization using CiteSpace, this study analyzed 324 papers published in the Web of Science Core Collection (WOSCC) from 1962 to 2023 and 353 core documents from China's three major databases (CNKI, Wanfang Database, and VIP Database). I. verum from Guangxi province towards various southern provinces in China, with autumn fruits exhibited superior quality and market value over their spring fruits. Literature in WOSCC emerged earlier, with a research emphasis on food science technology and pharmacology pharmacy domains. WOSCC research on I. verum could be divided into two phases: an embryonic period (1962-2001) and a growth period (2002-2023), showing an overall upward trend in publication. The three major Chinese databases contain a larger number of publications, with a focus on the food sector, which could be categorized into three stages: an embryonic period (1990-1999), a growth period (2000-2010), and a stable period (2011-2023), with an overall downward trend in publication. Both Chinese and international research hotspots converge on the medical applications of I. verum, with antioxidant bioactivity research emerging as a prevailing trend. This study delineated the resource distribution of I. verum across China and identified the research hotspots and trends both in China and internationally. The findings are beneficial for guiding researchers in swiftly establishing their research focus and furnishing decision-makers with a comprehensive reference for industry information.

Antimicrobial sensitisers: Gatekeepers to avoid the development of multidrug-resistant bacteria

The resistance of multidrug-resistant bacteria to existing antibiotics forces the continued development of new antibiotics and antibacterial agents, but the high costs and long timeframe involved in the development of new agents renders the hope that existing antibiotics may again play a part. The "antibiotic adjuvant" is an indirect antibacterial strategy, but its vague concept has, in the past, limited the development speed of related drugs. In this review article, we put forward an accurate concept of a "non-self-antimicrobial sensitisers (NSAS)", to distinguish it from an "antibiotic adjuvant", and then discuss several scientific methods to restore bacterial sensitivity to antibiotics, and the sources and action mechanism of existing NSAS, in order to guide the development and further research of NSAS.

Understanding the biofilm development of Acinetobacter baumannii and novel strategies to combat infection

Acinetobacter baumannii (A. baumannii) is a Gram-negative, nonmotile, and aerobic bacillus emerged as a superbug, due to increasing the possibility of infection and accelerating rates of antimicrobial agents. It is recognized as a nosocomial pathogen due to its ability to form biofilms. These biofilms serve as a defensive barrier, increase antibiotic resistance, and make treatment more difficult. As a result, the current situation necessitates the rapid emergence of novel therapeutic approaches to ensure successful treatment outcomes. This review explores the intricate relationship between biofilm formation and antibiotic resistance in A. baumannii, emphasizing the role of key virulence factors and quorum sensing (QS) mechanisms that will lead to infections and facilitate insight into developing innovative method to control A. baumannii infections. Furthermore, the review article looks into promising approaches for preventing biofilm formation on medically important surfaces and potential therapeutic methods for eliminating preformed biofilms, which can address biofilm-associated A. baumannii infections. Modern advances in emerging therapeutic options such as antimicrobial peptide (AMPs), nanoparticles (NPs), bacteriophage therapy, photodynamic therapy (PDT), and other biofilm inhibitors can assist readers understand the current landscape and future prospects for effectively treating A. baumannii biofilm infections.

Cell-free supernatants from Lactobacillus strains exert antibacterial, antibiofilm, and antivirulence activity against Pseudomonas aeruginosa from cystic fibrosis patients

Chronic lung infections caused by Pseudomonas aeruginosa play a significant role in the mortality and morbidity of cystic fibrosis (CF) patients. The widespread bacterial resistance to conventional antimicrobials demands identifying new strategies to complement or replace current antibiotic therapies. In this study, we evaluated the antibacterial, antibiofilm, and antivirulence properties of cell-free supernatants (CFS) from several Lactobacillus probiotic strains against P. aeruginosa isolated from the sputum of CF patients. A strong and fast antibacterial activity of CFS from different strains of lactobacilli was observed at acidic pH towards P. aeruginosa, both in planktonic and biofilm mode of growth, in conditions mimicking CF lung. Interestingly, although when adjusted at pH 6.0, CFS lost most of their antibacterial potential, they retained some antivirulence activity towards P. aeruginosa, largely dependent on the dose, exposure time, and the Lactobacillus-P. aeruginosa strain combination. In vivo testing in the invertebrate Galleria mellonella model disclosed the lack of toxicity of acidic CFS and their ability to prevent P. aeruginosa infection. For the first time, the results revealed lactobacilli postbiotic activities in the context of the pulmonary environment, pointing to innovative postbiotics' uses in anti-infective therapy.

In situ captured antibacterial action of membrane-incising peptide lamellae

Developing unique mechanisms of action are essential to combat the growing issue of antimicrobial resistance. Supramolecular assemblies combining the improved biostability of non-natural compounds with the complex membrane-attacking mechanisms of natural peptides are promising alternatives to conventional antibiotics. However, for such compounds the direct visual insight on antibacterial action is still lacking. Here we employ a design strategy focusing on an inducible assembly mechanism and utilized electron microscopy (EM) to follow the formation of supramolecular structures of lysine-rich heterochiral β3-peptides, termed lamellin-2K and lamellin-3K, triggered by bacterial cell surface lipopolysaccharides. Combined molecular dynamics simulations, EM and bacterial assays confirmed that the phosphate-induced conformational change on these lamellins led to the formation of striped lamellae capable of incising the cell envelope of Gram-negative bacteria thereby exerting antibacterial activity. Our findings also provide a mechanistic link for membrane-targeting agents depicting the antibiotic mechanism derived from the in-situ formation of active supramolecules.

Weissella sp. SNUL2 as potential probiotics with broad-spectrum antimicrobial activities

Probiotics have been applied to a wide range of bacteria, causing gastrointestinal and vaginal infections. However, probiotics generally possess limited antimicrobial spectra and are primarily utilized as dietary supplements. Recognizing the need for more versatile probiotics, this study focuses on isolating and characterizing strains suitable for antibiotic replacement. Among these strains, Weissella sp. SNUL2, derived from a traditional fermented food in Korea (i.e., Sikhae), emerged as a promising candidate. The correlation between optical density at 600 nm and colony-forming units was verified and applied in subsequent experiments. To assess the therapeutic potential of probiotics, antibacterial tests were conducted using a microplate reader to evaluate the inhibition of 60 bacterial strains (including common foodborne pathogens) induced by Weissella sp. SNUL2 cell-free supernatant (CFS). The results confirmed its broad-spectrum antibacterial properties compared to previously known probiotics. Furthermore, enzymatic treatment with proteinases (trypsin and pepsin) and a time-kill assay were conducted to elucidate the nature of the antibacterial substance in Weissella sp. SNUL2 CFS. Through sequential chromatography involving gel filtration and ion-exchange chromatography, specific fractions with enhanced antibacterial properties were identified. LC-MS/MS analysis of the secretome fraction revealed the presence of various proteins from the C39 family, peptidoglycan endopeptidases, and N-acetylmuramoyl-l-alanine amidase domain-containing protein precursors. Hence, the combined action of these proteins may contribute to Weissella sp. SNUL2's broad antimicrobial activity.

Exploiting predatory bacteria as biocontrol agents across ecosystems

Predatory bacteria have been increasingly known for their ubiquity in environments and great functional potentials in controlling unwanted microorganisms. Fundamental understanding of the predation mechanisms, population dynamics, and interaction patterns underlying bacterial predation is required for wise exploitation of predatory bacteria for enhancing ecoenvironmental, animal, and human health. Here, we review the recent achievements on applying predatory bacteria in different systems as biocontrol agents and living antibiotics as well as new findings in their phylogenetic diversity and predation mechanisms. We finally propose critical issues that deserve priority research and highlight the necessity to combine classic culture-based and advanced culture-independent approaches to push research frontiers of bacterial predation across ecosystems for promising biocontrol and therapy strategies towards a sustainable ecoenvironment and health.

Evaluation of the synergistic potential and mechanisms of action for de novo designed cationic antimicrobial peptides

Antimicrobial peptides (AMPs) have emerged as promising candidates in combating antimicrobial resistance - a growing issue in healthcare. However, to develop AMPs into effective therapeutics, a thorough analysis and extensive investigations are essential. In this study, we employed an in silico approach to design cationic AMPs de novo, followed by their experimental testing. The antibacterial potential of de novo designed cationic AMPs, along with their synergistic properties in combination with conventional antibiotics was examined. Furthermore, the effects of bacterial inoculum density and metabolic state on the antibacterial activity of AMPs were evaluated. Finally, the impact of several potent AMPs on E. coli cell envelope and genomic DNA integrity was determined. Collectively, this comprehensive analysis provides insights into the unique characteristics of cationic AMPs.

Preclinical characterization and in silico safety assessment of three virulent bacteriophages targeting carbapenem-resistant uropathogenic Escherichia coli

Phage therapy has recently been revitalized in the West with many successful applications against multi-drug-resistant bacterial infections. However, the lack of geographically diverse bacteriophage (phage) genomes has constrained our understanding of phage diversity and its genetics underpinning host specificity, lytic capability, and phage-bacteria co-evolution. This study aims to locally isolate virulent phages against uropathogenic Escherichia coli (E. coli) and study its phenotypic and genomic features. Three obligately virulent Escherichia phages (øEc_Makalu_001, øEc_Makalu_002, and øEc_Makalu_003) that could infect uropathogenic E. coli were isolated and characterized. All three phages belonged to Krischvirus genus. One-step growth curve showed that the latent period of the phages ranged from 15 to 20 min, the outbreak period ~ 50 min, and the burst size ranged between 74 and 127 PFU/bacterium. Moreover, the phages could tolerate a pH range of 6 to 9 and a temperature range of 25-37 °C for up to 180 min without significant loss of phage viability. All phages showed a broad host spectrum and could lyse up to 30% of the 35 tested E. coli isolates. Genomes of all phages were approximately ~ 163 kb with a gene density of 1.73 gene/kbp and an average gene length of ~ 951 bp. The coding density in all phages was approximately 95%. Putative lysin, holin, endolysin, and spanin genes were found in the genomes of all three phages. All phages were strictly virulent with functional lysis modules and lacked any known virulence or toxin genes and antimicrobial resistance genes. Pre-clinical experimental and genomic analysis suggest these phages may be suitable candidates for therapeutic applications.

Tracing the Antibacterial Performance of Bis-Imidazolium-based Ionic Liquid Derivatives

Ionic liquid (IL) cationic species have recently captivated the attention of pharmacists, biochemists, and biomedical scientists as promising antibacterial agents to deal with the multidrug resistance bacteria crisis. The structure and functional groups of ILs influence their physiochemical properties and biological activities. However, a comprehensive study is required to fully understand the details of the antibacterial activity of ILs carrying various functional groups. Herein, dicationic ILs (DCILs) are reported based on imidazolium rings as efficient antibacterial agents. The DCILs carried various functionalities such as 2-hydroxybutyl (DCIL-1), 2-hydroxy-3-isopropoxypropyl (DCIL-2), 2-hydroxy-3-(methacryloyloxy)propyl (DCIL-3), 2-hydroxy-2-phenylethyl (DCIL-4), and 2-hydroxy-3-phenoxypropyl (DCIL-5). The structure-antibacterial activity relationships of the DCILs against Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) were comprehensively studied through antibacterial tests, morphology analysis, and adhesion tests. The experimental assays revealed an antibacterial efficacy order of DCIL-5 > DCIL-1 > DCIL-4 > DCIL-2 > DCIL-3. The all-atom molecular dynamics (MD) simulation showed a deep permeation of the hydrophobic -OPh functional group of DCIL-5 through the E. coli membrane model in agreement with the experimental observations. Current findings assist scientists in designing new task-specific DCILs for effective interactions with biological membranes for different applications.

A novel bioinformatic method for the identification of antimicrobial peptides in metagenomes

AIMS

This study aimed to develop a new bioinformatic approach for the identification of novel antimicrobial peptides (AMPs), which did not depend on sequence similarity to known AMPs held within databases, but on structural mimicry of another antimicrobial compound, in this case an ultrashort, synthetic, cationic lipopeptide (C12-OOWW-NH2).

METHODS AND RESULTS

When applied to a collection of metagenomic datasets, our outlined bioinformatic method successfully identified several short (8-10aa) functional AMPs, the activity of which was verified via disk diffusion and minimum inhibitory concentration assays against a panel of 12 bacterial strains. Some peptides had activity comparable to, or in some cases, greater than, those from published studies that identified AMPs using more conventional methods. We also explored the effects of modifications, including extension of the peptides, observing an activity peak at 9-12aa. Additionally, the inclusion of a C-terminal amide enhanced activity in most cases. Our most promising candidate (named PB2-10aa-NH2) was thermally stable, lipid-soluble, and possessed synergistic activity with ethanol but not with a conventional antibiotic (streptomycin).

CONCLUSIONS

While several bioinformatic methods exist to predict AMPs, the approach outlined here is much simpler and can be used to quickly scan huge datasets. Searching for peptide sequences bearing structural similarity to other antimicrobial compounds may present a further opportunity to identify novel AMPs with clinical relevance, and provide a meaningful contribution to the pressing global issue of AMR.

Refining antimicrobial photodynamic therapy: effect of charge distribution and central metal ion in fluorinated porphyrins on effective control of planktonic and biofilm bacterial forms

Antibiotic resistance represents a pressing global health challenge, now acknowledged as a critical concern within the framework of One Health. Photodynamic inactivation of microorganisms (PDI) offers an attractive, non-invasive approach known for its flexibility, independence from microbial resistance patterns, broad-spectrum efficacy, and minimal risk of inducing resistance. Various photosensitizers, including porphyrin derivatives have been explored for pathogen eradication. In this context, we present the synthesis, spectroscopic and photophysical characteristics as well as antimicrobial properties of a palladium(II)-porphyrin derivative (PdF2POH), along with its zinc(II)- and free-base counterparts (ZnF2POH and F2POH, respectively). Our findings reveal that the palladium(II)-porphyrin complex can be classified as an excellent generator of reactive oxygen species (ROS), encompassing both singlet oxygen (Φ△ = 0.93) and oxygen-centered radicals. The ability of photosensitizers to generate ROS was assessed using a variety of direct (luminescence measurements) and indirect techniques, including specific fluorescent probes both in solution and in microorganisms during the PDI procedure. We investigated the PDI efficacy of F2POH, ZnF2POH, and PdF2POH against both Gram-negative and Gram-positive bacteria. All tested compounds proved high activity against Gram-positive species, with PdF2POH exhibiting superior efficacy, leading to up to a 6-log reduction in S. aureus viability. Notably, PdF2POH-mediated PDI displayed remarkable effectiveness against S. aureus biofilm, a challenging target due to its complex structure and increased resistance to conventional treatments. Furthermore, our results show that PDI with PdF2POH is more selective for bacterial than for mammalian cells, particularly at lower light doses (up to 5 J/cm2 of blue light illumination). This enhanced efficacy of PdF2POH-mediated PDI as compared to ZnF2POH and F2POH can be attributed to more pronounced ROS generation by palladium derivative via both types of photochemical mechanisms (high yields of singlet oxygen generation as well as oxygen-centered radicals). Additionally, PDI proved effective in eliminating bacteria within S. aureus-infected human keratinocytes, inhibiting infection progression while preserving the viability and integrity of infected HaCaT cells. These findings underscore the potential of metalloporphyrins, particularly the Pd(II)-porphyrin complex, as promising photosensitizers for PDI in various bacterial infections, warranting further investigation in advanced infection models.

Silver Nanoparticles-Chitosan Nanocomposites: A Comparative Study Regarding Different Chemical Syntheses Procedures and Their Antibacterial Effect

Nanocomposites based on silver nanoparticles and chitosan present important advantages for medical applications, showing over time their role in antibacterial evaluation. This work presents the comparative study of two chemical synthesis procedures of nanocomposites, based on trisodium citrate dihydrate and sodium hydroxide, using various chitosan concentrations for a complex investigation. The nanocomposites were characterized by AFM and DLS regarding their dimensions, while FT-IR and UV-VIS spectrometry were used for the optical properties and to reveal the binding of silver nanoparticles with chitosan. Their antibacterial effect was determined using a disk diffusion method on two bacteria strains, E. coli and S. aureus. The results indicate that, when using both methods, the nanocomposites obtained were below 100 nm, yet the antibacterial effect proved to be stronger for the nanocomposites obtained using sodium hydroxide. Furthermore, the antibacterial effect can be related to the nanocomposites' sizes, since the smallest dimension nanocomposites exhibited the best bacterial growth inhibition on both bacteria strains we tested and for both types of silver nanocomposites.

Juglone as a Natural Quorum Sensing Inhibitor against Pseudomonas aeruginosa pqs-Mediated Virulence and Biofilms

Pseudomonas aeruginosa is a notorious opportunistic pathogen associated with chronic biofilm-related infections, posing a significant challenge to effective treatment strategies. Quorum sensing (QS) and biofilm formation are critical virulence factors employed by P. aeruginosa, contributing to its pathogenicity and antibiotic resistance. Other than the homoserine-based QS systems, P. aeruginosa also possesses the quinolone-based Pseudomonas quinolone signal (PQS) QS signaling. Synthesis of the PQS signaling molecule is achieved by the pqsABCDEH operon, whereas the PQS signaling response was mediated by the PqsR receptor. In this study, we report the discovery of a novel natural compound, Juglone, with potent inhibitory effects on pqs QS and biofilm formation in P. aeruginosa. Through an extensive screening of natural compounds from diverse sources, we identified Juglone, a natural compound from walnut, as a promising candidate. We showed that Juglone could inhibit PqsR and the molecular docking results revealed that Juglone could potentially bind to the PqsR active site. Furthermore, Juglone could inhibit pqs-regulated virulence factors, such as pyocyanin and the PQS QS signaling molecule. Juglone could also significantly reduce both the quantity and quality of P. aeruginosa biofilms. Notably, this compound exhibited minimal cytotoxicity toward mammalian cells, suggesting its potential safety for therapeutic applications. To explore the clinical relevance of Juglone, we investigated its combinatorial effects with colistin, a commonly used antibiotic against P. aeruginosa infections. The Juglone-colistin combinatorial treatment could eliminate biofilms formed by wild-type P. aeruginosa PAO1 and its clinical isolates collected from cystic fibrosis patients. The Juglone-colistin combinatorial therapy dramatically improved colistin efficacy and reduced inflammation in a wound infection model, indicating its potential for clinical utility. In conclusion, the discovery of Juglone provides insights into the development of innovative antivirulence therapeutic strategies to combat P. aeruginosa biofilm-associated infections.

Coassembled Multicomponent Protein Nanoparticles Elicit Enhanced Antibacterial Activity

The waning pipeline of the useful antibacterial arsenal has necessitated the urgent development of more effective antibacterial strategies with distinct mechanisms to rival the continuing emergence of resistant pathogens, particularly Gram-negative bacteria, due to their explicit drug-impermeable, two-membrane-sandwiched cell wall envelope. Herein, we have developed multicomponent coassembled nanoparticles with strong bactericidal activity and simultaneous bacterial cell envelope targeting using a peptide coassembly strategy. Compared to the single-component self-assembled nanoparticle counterparts or cocktail mixtures of these at a similar concentration, coassembled multicomponent nanoparticles showed higher bacterial killing efficiency against Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli by several orders of magnitude (about 100-1,000,000-fold increase). Comprehensive confocal and electron microscopy suggest that the superior antibacterial activity of the coassembled nanoparticles proceeds via multiple complementary mechanisms of action, including membrane destabilization, disruption, and cell wall hydrolysis, actions that were not observed with the single nanoparticle counterparts. To understand the fundamental working mechanisms behind the improved performance of coassembled nanoparticles, we utilized a "dilution effect" system where the antibacterial components are intermolecularly mixed and coassembled with a non-antibacterial protein in the nanoparticles. We suggest that coassembled nanoparticles mediate enhanced bacterial killing activity by attributes such as optimized local concentration, high avidity, cooperativity, and synergy. The nanoparticles showed no cytotoxic or hemolytic activity against tested eukaryotic cells and erythrocytes. Collectively, these findings reveal potential strategies for disrupting the impermeable barrier that Gram-negative pathogens leverage to restrict antibacterial access and may serve as a platform technology for potential nano-antibacterial design to strengthen the declining antibiotic arsenal.

Confronting antibiotic-resistant pathogens: Distinctive drug delivery potentials of progressive nanoparticles

Antimicrobial resistance arises over time, usually due to genetic modifications. Global observations of high resistance rates to popular antibiotics used to treat common bacterial diseases, such as diarrhea, STIs, sepsis, and urinary tract infections, indicate that our supply of effective antibiotics is running low. The mechanisms of action of several antibiotic groups are covered in this review. Antimicrobials disrupt the development and metabolism of bacteria, leading to their eventual death. However, in recent years, microorganisms become resistant to the drugs. Bacteria encode resistant genes against antibiotics and inhibit the function of antibiotics by reducing the uptake of drugs, modifying the enzyme's active site, synthesizing enzymes to degrade antibiotics, and changing the structure of ribosomal subunits. Additionally, the methods of action of resistant bacteria against different kinds of antibiotics as well as their modes of action are discussed. Besides, the resistant pathogenic bacteria which get the most priority by World Health Organisation (WHO) for synthesizing new drugs, have also been incorporated. To overcome antimicrobial resistance, nanomaterials are used to increase the efficacy of antimicrobial drugs. Metallic, inorganic, and polymer-based nanoparticles once conjugated with antibacterial drugs, exhibit synergistic effects by increasing the efficacy of the drugs by inhibiting bacterial growth. Nanomaterial's toxic properties are proportional to their concentrations. Higher concentration nanomaterials are more toxic to the cells. In this review, the toxic properties of nanomaterials on lung cells, lymph nodes, and neuronal cells are also summarized.

Facile Construction of Antimicrobial Surface via One-Step Co-Deposition of Peptide Polymer and Dopamine

The infections associated with implantable medical devices can greatly affect the therapeutic effect and impose a heavy financial burden. Therefore, it is of great significance to develop antimicrobial biomaterials for the prevention and mitigation of healthcare-associated infections. Here, a facile construction of antimicrobial surface via one-step co-deposition of peptide polymer and dopamine is reported. The co-deposition of antimicrobial peptide polymer DLL60 BLG40 with dopamine (DA) on the surface of thermoplastic polyurethane (TPU) provides peptide polymer-modified TPU surface (TPU-DLL60 BLG40 ). The antimicrobial test shows that the TPU-DLL60 BLG40 surfaces of the sheet and the catheter both exhibit potent killing of 99.9% of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). In addition, the TPU-DLL60 BLG40 surface also exhibits excellent biocompatibility. This one-step antimicrobial modification method is fast and efficient, implies promising application in surface antimicrobial modification of implantable biomaterials and medical devices.

Toward Clinical Applications: Transforming Nonantibiotic Antibacterials into Effective Next-Generation Supramolecular Therapeutics

Antibiotic resistance is a major driver of morbidity and mortality worldwide, necessitating alternatives. Due to their mechanism of action, bacteriophages, endolysins, and antimicrobial peptides (coined herein as nonantibiotic antibacterials, NAA) have risen to tackle this problem and led to paradigms in treating antibiotic-resistant bacterial infections. However, their clinical applications remain challenging and have been seriously hampered by cytotoxicity, instability, weak bioactivity, low on-target bioavailability, high pro-inflammatory responses, shorter half-life, and circulatory properties. Hence, to transit preclinical phases and beyond, it has become imperative to radically engineer these alternatives into innovative and revolutionary therapeutics to overcome recalcitrant infections. This perspective highlights the promise of these agents, their limitations, promising designs, nanotechnology, and delivery approaches that can be harnessed to transform these agents. Finally, I provide an outlook on the remaining challenges that need to be tackled for their widespread clinical administration.

CAR Immunotherapy for the treatment of infectious diseases: a systematic review

Immunotherapy treatments aim to modulate the host's immune response to either mitigate it in inflammatory/autoimmune disease or enhance it against infection or cancer. Among different immunotherapies reaching clinical application during the last years, chimeric antigen receptor (CAR) immunotherapy has emerged as an effective treatment for cancer where different CAR T cells have already been approved. Yet their use against infectious diseases is an area still relatively poorly explored, albeit with tremendous potential for research and clinical application. Infectious diseases represent a global health challenge, with the escalating threat of antimicrobial resistance underscoring the need for alternative therapeutic approaches. This review aims to systematically evaluate the current applications of CAR immunotherapy in infectious diseases and discuss its potential for future applications. Notably, CAR cell therapies, initially developed for cancer treatment, are gaining recognition as potential remedies for infectious diseases. The review sheds light on significant progress in CAR T cell therapy directed at viral and opportunistic fungal infections.

Unraveling the Effects of Cationic Peptides on Vesicle Structures: Insights into Peptide-Membrane Interactions

Antimicrobial resistance is a pressing global health issue, with millions of lives at risk by 2050, necessitating the development of alternatives with broad-spectrum activity against pathogenic microbes. Antimicrobial peptides provide a promising solution by combating microbes, modulating immunity, and reducing resistance development through membrane and intracellular targeting. PuroA, a synthetic peptide derived from the tryptophan-rich domain of puroindoline A, exhibits potent antimicrobial activity against various pathogens, while the rationally designed P1 peptide demonstrates enhanced antimicrobial activity with its specific composition. This paper investigates the concentration-dependent effects of these cationic peptides on distinct types of vesicles representing strong-negative bacterial cell membranes (S-vesicles), weak-negative bacterial cell membranes (W-vesicles), and mammalian cell membranes (M-vesicles). To investigate the interactions between the peptides and vesicles, small-angle neutron scattering experiments were conducted. The cationic peptides, PuroA and P1, interact with S-vesicles through electrostatic interactions, leading to distinct effects. PuroA accumulates on the vesicle surface, increasing Rcore and Rtotal, aligning with the carpet model. P1 disrupts the vesicle structure at higher concentrations, consistent with the detergent model. Neither peptide significantly affects W-vesicles, emphasizing the role of charge. In uncharged M-vesicles, both peptides decrease Rcore and Rtotal and increase tshell, indicating peptide insertion and altered bilayer properties. These findings provide valuable insights into peptide-membrane interactions and their impact on vesicle structures. Furthermore, the implications of these findings extend to the potential development of innovative antimicrobial agents and drug delivery systems that specifically target bacterial and mammalian membranes. This research contributes to the advancement of understanding peptide-membrane interactions and lays the foundation for the design of approaches for targeting membranes in various biomedical applications.

Bifunctional Carbosilane Dendrimers for the Design of Multipurpose Hydrogels with Antibacterial Action

The emergence of antibiotic resistance is a serious global health problem. There is an incessant demand for new antimicrobial drugs and materials that can address this global issue from different angles. Dendritic hydrogels have appeared as a promising strategy. A family of bifunctional amphiphilic carbosilane dendrimers was designed and employed as nanosized cross-linking points for the synthesis of high-swelling hydrogels using the highly efficient Thiol-Ene click reaction for their preparation. Both stoichiometric and off-stoichiometric conditions were studied, generating hydrogels with pendant hydroxyl or alkene moieties. These hydrogels were found to be tunable antibacterial materials. They can easily be postmodified with relevant antibiotic moieties through covalent attachment on the hydroxyl or alkene pendant groups, generating ammonium-decorated networks with temperature and pH-responsive properties. Additionally, they can efficiently encapsulate drugs with poor solubility in water, like ciprofloxacin, and perform a sustained release over time, as demonstrated in preliminary assays against Staphylococcus aureus.

All-Natural Injectable Antibacterial Hydrogel Enabled by Chitosan and Borneol

Hydrogels with intrinsic antimicrobial capabilities based on natural strategies have been studied as a hot topic in biomedicine. Nevertheless, it is highly challenging to thoroughly develop a bacteriostatic natural hydrogel. Borneol as a traditional Chinese medicine possesses a unique broad-spectrum antibacterial activity under a membrane-breaking mechanism. In this study, a range of fully natural antibacterial hydrogels are designed and synthesized via the Schiff base cross-linking of carboxymethyl chitosan and dialdehyde dextran grafted natural borneol. The borneol with three configurations is hydrophilically modified onto dextran to boost its antibacterial activity. Also, the synergism of hydrophilic-modified borneol groups and positively charged ammonium ions of carboxymethyl chitosan make the hydrogels totally constrict the E. coli and S. aureus growth during 24 h. Furthermore, the hydrogels exhibit good in vitro cytocompatibility through cytotoxicity, protein adhesion, and hemolytic tests. In view of the injectability, the hydrogels can be delivered to the target site through a minimally invasive route. In short, this work offers a potential tactic to develop antibacterial hydrogels for the treatment of topical wound infections.

Positive and negative aspects of bacteriophages and their immense role in the food chain

Bacteriophages infect and replicate inside a bacterial host as well as serve as natural bio-control agents. Phages were once viewed as nuisances that caused fermentation failures with cheese-making and other industrial processes, which lead to economic losses, but phages are now increasingly being observed as being promising antimicrobials that can fight against spoilage and pathogenic bacteria. Pathogen-free meals that fulfil industry requirements without synthetic additives are always in demand in the food sector. This study introduces the readers to the history, sources, and biology of bacteriophages, which include their host ranges, absorption mechanisms, lytic profiles, lysogenic profiles, and the influence of external factors on the growth of phages. Phages and their derivatives have emerged as antimicrobial agents, biodetectors, and biofilm controllers, which have been comprehensively discussed in addition to their potential applications in the food and gastrointestinal tract, and they are a feasible and safe option for preventing, treating, and/or eradicating contaminants in various foods and food processing environments. Furthermore, phages and phage-derived lytic proteins can be considered potential antimicrobials in the traditional farm-to-fork context, which include phage-based mixtures and commercially available phage products. This paper concludes with some potential safety concerns that need to be addressed to enable bacteriophage use efficiently.

Alternatives to antibiotics in pig production: looking through the lens of immunophysiology

In the livestock production system, the evolution of porcine gut microecology is consistent with the idea of "The Hygiene Hypothesis" in humans. I.e., improved hygiene conditions, reduced exposure to environmental microorganisms in early life, and frequent use of antimicrobial drugs drive immune dysregulation. Meanwhile, the overuse of antibiotics as feed additives for infectious disease prevention and animal growth induces antimicrobial resistance genes in pathogens and spreads related environmental pollutants. It justifies our attempt to review alternatives to antibiotics that can support optimal growth and improve the immunophysiological state of pigs. In the current review, we first described porcine mucosal immunity, followed by discussions of gut microbiota dynamics during the critical weaning period and the impacts brought by antibiotics usage. Evidence of in-feed additives with immuno-modulatory properties highlighting probiotics, prebiotics, and phytobiotics and their cellular and molecular networking are summarized and reviewed. It may provide insights into the immune regulatory mechanisms of antibiotic alternatives and open new avenues for health management in pig production.

Impact of an oligosaccharide-based polymer on the metabolic profiles and microbial ecology of weanling pigs experimentally infected with a pathogenic E. coli

BACKGROUND

Our previous study has reported that supplementation of oligosaccharide-based polymer enhances gut health and disease resistance of pigs infected with enterotoxigenic E. coli (ETEC) F18 in a manner similar to carbadox. The objective of this study was to investigate the impacts of oligosaccharide-based polymer or antibiotic on the host metabolic profiles and colon microbiota of weaned pigs experimentally infected with ETEC F18.

RESULTS

Multivariate analysis highlighted the differences in the metabolic profiles of serum and colon digesta which were predominantly found between pigs supplemented with oligosaccharide-based polymer and antibiotic. The relative abundance of metabolic markers of immune responses and nutrient metabolisms, such as amino acids and carbohydrates, were significantly differentiated between the oligosaccharide-based polymer and antibiotic groups (q < 0.2 and fold change > 2.0). In addition, pigs in antibiotic had a reduced (P < 0.05) relative abundance of Lachnospiraceae and Lactobacillaceae, whereas had greater (P < 0.05) Clostridiaceae and Streptococcaceae in the colon digesta on d 11 post-inoculation (PI) compared with d 5 PI.

CONCLUSIONS

The impact of oligosaccharide-based polymer on the metabolic and microbial profiles of pigs is not fully understood, and further exploration is needed. However, current research suggest that various mechanisms are involved in the enhanced disease resistance and performance in ETEC-challenged pigs by supplementing this polymer.

Small molecular adjuvants repurpose antibiotics towards Gram-negative bacterial infections and multispecies bacterial biofilms

Gram-negative bacterial infections pose a significant challenge due to two major resistance elements, including the impermeability of the outer membrane and the overexpression of efflux pumps, which contribute to antibiotic resistance. Additionally, the coexistence of multispecies superbugs in mixed species biofilms further complicates treatment, as these infections are refractory to most antibiotics. To address this issue, combining obsolete antibiotics with non-antibiotic adjuvants that target bacterial membranes has shown promise in combating antibacterial resistance. However, the clinical translation of this cocktail therapy has been hindered by the toxicity associated with these membrane active adjuvants, mainly due to a limited understanding of their structure and mechanism of action. Towards this goal, herein, we have designed a small molecular adjuvant by tuning different structural parameters, such as the balance between hydrophilic and hydrophobic groups, spatial positioning of hydrophobicity and hydrogen bonding interactions, causing moderate membrane perturbation in bacterial cells without any toxicity to mammalian cells. Moderate membrane perturbation not only enhances the internalization of antibiotics, but also increases the intracellular concentration of drugs by hampering the efflux machinery. This revitalises the efficacy of various classes of antibiotics by 32-512 fold, without inducing toxicity. The leading combination not only exhibits potent bactericidal activity against A. baumannii biofilms but also effectively disrupts mature multispecies biofilms composed of A. baumannii and methicillin-resistant Staphylococcus aureus (MRSA), which is typically resistant to most antibiotics. Importantly, the combination therapy demonstrates good biocompatibility and excellent in vivo antibacterial efficacy (>99% reduction) in a skin infection model of A. baumannii. Interestingly, A. baumannii shows reduced susceptibility to develop resistance against the leading combination, underscoring its potential for treating multi-drug resistant infections.

Bactericidal and non-cytotoxic activity of bacteriocin produced by Lacticaseibacillus paracasei F9-02 and evaluation of its tolerance to various physico-chemical conditions

This study aims to explore novel lactic acid bacteria (LAB) from breast-fed infants' faeces towards characterizing their antimicrobial compound, bacteriocin. The LAB, Lacticaseibacillus paracasei F9-02 showed strong antimicrobial activity against clinical pathogens. Their proteinaceous nature was confirmed as the activity was completely abolished when treated with proteinaceous enzymes and retained during neutral pH and catalase treatment. The purified bacteriocin showed antimicrobial activity at the minimum inhibitory concentration (MIC) value of 7.56 μg/ml against vancomycin-resistant Enterococcus sp. [vancomycin-resistant enterococcal (VRE)], and methicillin-resistant Staphylococcus aureus (MRSA), 15.13 μg/ml against Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica serotype typhi and 30.25 μg/ml against Shigella flexneri. Present study also proved the bactericidal, non-cytotoxic and non-hemolytic nature of bacteriocin. Additionally, bacteriocin retained their stability under various physico-chemical conditions, broad range of pH (2-10), temperature (40-121°C), enzymes (amylase, lipase and lysozyme), surfactants [Tween-20, 80, 100 and sodium dodecyl sulfate (SDS)], metal ions (CaCl2 , FeSO4 , ZnSO4 , MgSO4 , MnSO4 , CuCl2 ) and NaCl (2%-8%). The molecular weight of bacteriocin (~28 kDa) was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), functional and active groups were assessed by Fourier Transform-Infrared (FT-IR). To our knowledge, this is the first study reporting L. paracasei from breast-fed infants' faeces and assessing their antimicrobial compound, bacteriocin. The study results furnish the essential features to confirm the therapeutic potential of L. paracasei F9-02 bacteriocin.

Enhanced antibacterial activity of dimethyl gallium quinolinolates toward drug-resistant Klebsiella pneumoniae in low iron environments

A series of dimethylgallium quinolinolate [GaMe2L] (L = 5-chloroquinolinolate, 5, 7-dichloroquinolinolate, 5, 7-dibromoquinolinolate or 5, 7-doiodoquinolinolate) complexes, shown previously to be active toward the Leishmania parasite, have been studied for their antibacterial activity toward a reference and drug resistant strain of Klebsiella pneumoniae (KP). The assays were conducted in standard iron-rich LB media and in the iron depleted RPMI and RPMI-HS media to better understand the effect of Fe concentration on the activity of the Ga complexes. In LB broth the parent quinolinols and the gallium complexes were inactive up to the highest concentration tested, 100 μM. In the more physiologically relevant 'iron-poor' RPMI-HS media the quinolonols remained inactive, however, the gallium complexes showed exceptional activity in the range 48-195 nM. Only in RPMI without any added HS did both the quinolinols and the gallium complexes show good activity. The significant differences in activity across the various media types suggest that the unnaturally high iron content of conventional LB media may provide false negative results for potentially potent Ga therapeutics. A protein binding assay on the organometallic gallium complexes showed a much slower uptake of Ga by Fe-binding proteins than is typically observed for gallium salts. This indicates that their greater lipophilicity and greater hydrolytic stability could account for their increased biological activity in RPMI-HS media.

A review on the effects of discharging conventionally treated livestock waste to the environmental resistome

Globally, animal production has developed rapidly as a consequence of the ongoing population growth, to support food security. This has consequently led to an extensive use of antibiotics to promote growth and prevent diseases in animals. However, most antibiotics are not fully metabolized by these animals, leading to their excretion within urine and faeces, thus making these wastes a major reservoir of antibiotics residues, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the environment. Farmers normally depend on conventional treatment methods to mitigate the environmental impact of animal waste; however, these methods are not fully efficient to remove the environmental resistome. The present study reviewed the variability of residual antibiotics, ARB, as well as ARGs in the conventionally treated waste and assessed how discharging it could increase resistome in the receiving environments. Wherein, considering the efficiency and environmental safety, an addition of pre-treatments steps with these conventional treatment methods could enhance the removal of antibiotic resistance agents from livestock waste.

Characterization of a Vibriophage Infecting Pathogenic Vibrio harveyi

Bacterial diseases caused by Vibrio spp. are prevalent in aquaculture and can lead to high mortality rates among aquatic species and significant economic losses. With the increasing emergence of multidrug-resistant Vibrio strains, phage therapy is being explored as a potential alternative to antibiotics for biocontrol of infectious diseases. Here, a new lytic phage named vB_VhaS_R21Y (R21Y) was isolated against Vibrio harveyi BVH1 obtained from seawater from a scallop-farming area in Rongcheng, China. Its morphology, infection cycle, lytic profile, phage stability, and genetic features were characterized. Transmission electronic microscopy indicated that R21Y is siphovirus-like, comprising an icosahedral head (diameter 73.31 ± 2.09 nm) and long noncontractile tail (205.55 ± 0.75 nm). In a one-step growth experiment, R21Y had a 40-min latent period and a burst size of 35 phage particles per infected cell. R21Y was highly species-specific in the host range test and was relatively stable at pH 4-10 and 4-55 °C. Genomic analysis showed that R21Y is a double-stranded DNA virus with a genome size of 82,795 bp and GC content of 47.48%. Its high tolerance and lytic activity indicated that R21Y may be a candidate for phage therapy in controlling vibriosis in aquacultural systems.

De novo designed self-assembling helicomimetic lipooligoureas with antibacterial activity

The overuse of antibiotics has led to a rise in infections caused by multidrug-resistant bacteria, resulting in a need for new antibacterial compounds with different modes of action. In this paper, we describe a new class of compounds called lipooligoureas, which are foldamer-based mimetics of antimicrobial lipopeptides. The lipooligoureas consist of an acyl chain connected to the N-terminus of an oligourea head group that exhibits a well-defined 2.5-helix secondary structure, which is further stabilized by the attachment of the lipophilic chain to the oligourea moiety. These compounds meet the established criteria for membranolytic compounds by possessing an amphiphilic structure that promotes the internalization and partitioning of the molecules into the lipid membrane. The presence of positively charged urea residues promotes electrostatic interactions with the negatively charged bacterial membrane. The subtle structural differences in oligourea head group influence the compounds' aggregation behavior, with the number and position of positively charged urea residues correlating with their aggregation ability. The biological activity of these compounds in inhibiting bacterial growth is correlated with their ability to aggregate, with stronger antibacterial properties exhibited by those that aggregate more easily. However, the concentration inhibiting bacterial growth is significantly lower than the critical aggregation concentration values, suggesting that the mechanism of action involves the monomeric forms of lipooligoureas. Nonetheless, a mechanism based on membrane-induced aggregation cannot be ruled out. The lipooligoureas exhibit higher activity towards Gram-positive bacteria than against Gram-negative bacteria, which is indicative of certain selectivity of these compounds. It is also demonstrated that lipooligoureas exhibit increased stability against proteolytic degradation in human blood serum.

Bovine Lactoferrin and Current Antifungal Therapy Against Candida Albicans: A Systematic Review and Meta-Analysis

Candida albicans is an important causative organism of opportunistic fungal infection, and it is a growing medical concern due to the increasing usage of broad-spectrum antibiotics, immunosuppressant agents, and other immunocompromising conditions. Currently, bLf and antifungal drugs have been known to have synergistic effects, increasing the drug's efficacy. This study aims to investigate the efficacy of the synergistic effect of bLf and antifungal drugs. This review addressed the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. We conducted literature searches to assess the association of lactoferrin and current antifungal therapy against Candida albicans in ProQuest, PubMed, MEDLINE, EBSCOhost, SAGE, JSTOR, GARUDA, and Open Gray with no date restriction (until March 5th, 2021). We used Jeffry's Amazing Statistical Program (JASP) to measure the overall size effect of MIC (minimum inhibitory concentration) between studies. A total of 7 studies retained were experimental in vitro studies. Based on the available data, 4 out of 7 studies were included in the quantitative analysis. This systematic review showed that bovine lactoferrin could help inhibit the development of azole-susceptible and azole-resistant C. albicans. Furthermore, there was synergistic activity between lactoferrin and various antifungals. Our meta-analysis showed that lactoferrin could significantly inhibit the C. albicans growth than the control group. Bovine lactoferrin and its peptide derivatives isolated from bovine milk can significantly inhibit the growth of C. albicans, both susceptible to azoles and those with azole resistance.

Synthesis and Biological Activity of Antimicrobial Agents, 2nd Volume

Microorganisms are abundant and necessary [...].

The increasing importance of novel deep eutectic solvents as potential effective antimicrobials and other medicinal properties

With the rise of antibiotic resistance globally, coupled with evolving and emerging infectious diseases, there is an urgent need for the development of novel antimicrobials. Deep eutectic solvents (DES) are a new generation of eutectic mixtures that depict promising attributes with several biological implications. DES exhibit unique properties such as low toxicity, biodegradability, and high thermal stability. Herein, the antimicrobial properties of DES and their mechanisms of action against a range of microorganisms, including bacteria, amoebae, fungi, viruses, and anti-cancer properties are reviewed. Overall, DES represent a promising class of novel antimicrobial agents as well as possessing other important biological attributes, however, future studies on DES are needed to investigate their underlying antimicrobial mechanism, as well as their in vivo effects, for use in the clinic and public at large.

Rifampicin-resistant RpoB S522L Vibrio vulnificus exhibits disturbed stress response and hypervirulence traits

Rifampicin resistance, which is genetically linked to mutations in the RNA polymerase β-subunit gene rpoB, has a global impact on bacterial transcription and cell physiology. Previously, we identified a substitution of serine 522 in RpoB (i.e., RpoBS522L ) conferring rifampicin resistance to Vibrio vulnificus, a human food-borne and wound-infecting pathogen associated with a high mortality rate. Transcriptional and physiological analysis of V. vulnificus expressing RpoBS522L showed increased basal transcription of stress-related genes and global virulence regulators. Phenotypically these transcriptional changes manifest as disturbed osmo-stress responses and toxin-associated hypervirulence as shown by reduced hypoosmotic-stress resistance and enhanced cytotoxicity of the RpoBS522L strain. These results suggest that RpoB-linked rifampicin resistance has a significant impact on V. vulnificus survival in the environment and during infection.

Facial amphiphilic naphthoic acid-derived antimicrobial polymers against multi-drug resistant gram-negative bacteria and biofilms

Inspired by the facial amphiphilic nature and antimicrobial efficacy of many antimicrobial peptides, this work reported facial amphiphilic bicyclic naphthoic acid derivatives with different ratios of charges to rings that were installed onto side chains of poly(glycidyl methacrylate). Six quaternary ammonium-charged (QAC) polymers were prepared to investigate the structure-activity relationship. These QAC polymers displayed potent antibacterial activity against various multi-drug resistant (MDR) gram-negative pathogens such as Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. Polymers demonstrated low hemolysis and high antimicrobial selectivity. Additionally, they were able to eradicate established biofilms and kill metabolically inactive dormant cells. The membrane permeabilization and depolarization results indicated a mechanism of action through membrane disruption. Two lead polymers showed no resistance from MDR-P. aeruginosa and MDR-K. pneumoniae. These facial amphiphiles are potentially a new class of potent antimicrobial agents to tackle the antimicrobial resistance for both planktonic and biofilm-related infections.

Detection of heat-stable antibacterial activity in cotyledonary and discoid placentas

The placenta serves in immunological defense of the fetus, providing proteins essential for innate immunity. Maternal and fetal portions of two mammalian placenta types, discoid, and cotyledonary, were separated and analyzed for antibacterial activity using a culture-independent method. Antibacterial activity was detected in both maternal and fetal portions of all placenta types tested. Protease resistance and increased activity after boiling suggests that the factor is activated upon release from a larger molecule. Identification of this factor and the mechanism of activation will lead to a better understanding of the innate immune function provided by the placenta.

Host-directed therapy for bacterial infections -Modulation of the phagolysosome pathway

Bacterial infections still impose a significant burden on humanity, even though antimicrobial agents have long since been developed. In addition to individual severe infections, the f fatality rate of sepsis remains high, and the threat of antimicrobial-resistant bacteria grows with time, putting us at inferiority. Although tremendous resources have been devoted to the development of antimicrobial agents, we have yet to recover from the lost ground we have been driven into. Looking back at the evolution of treatment for cancer, which, like infectious diseases, has the similarity that host immunity eliminates the lesion, the development of drugs to eliminate the tumor itself has shifted from a single-minded focus on drug development to the establishment of a treatment strategy in which the de-suppression of host immunity is another pillar of treatment. In infectious diseases, on the other hand, the development of therapies that strengthen and support the immune system has only just begun. Among innate immunity, the first line of defense that bacteria encounter after invading the host, the molecular mechanisms of the phagolysosome pathway, which begins with phagocytosis to fusion with lysosome, have been elucidated in detail. Bacteria have a large number of strategies to escape and survive the pathway. Although the full picture is still unfathomable, the molecular mechanisms have been elucidated for some of them, providing sufficient clues for intervention. In this article, we review the host defense mechanisms and bacterial evasion mechanisms and discuss the possibility of host-directed therapy for bacterial infection by intervening in the phagolysosome pathway.