The antimicrobial peptide SAAP-148 combats drug-resistant bacteria and biofilms

Gelatin emulsion gels loaded with host defence peptides for the treatment of antibiotic-resistant infections

The surge in multidrug-resistant bacteria against conventional antibiotics is a rapidly developing global health crisis necessitating novel infection management strategies. Host defence peptides (HDPs), also known as antimicrobial peptides (AMPs), offer a promising alternative to traditional antibiotics, but their practical translation is limited by their susceptibility to proteases and potential off-site cytotoxicity. In this paper, we investigate the feasibility of using gelatin emulsion gels (GELs), prepared using a water-in-oil (W/O) method, for the delivery of HDPs DJK-5 and IDR-1018 to improve their clinical utility. DJK-5-loaded GELs exhibited complete eradication of planktonic Methicillin-resistant Staphylococcus aureus (MRSA) at 4 - and 24-h intervals. Similarly, IDR-1018-loaded GELs demonstrated almost complete killing of MRSA and Escherichia coli (E. coli) after 4 h. Importantly, none of the GEL formulations investigated exhibited in vitro cytotoxicity. Overall, these HDP loaded GELs are a promising solution for the treatment of antibiotic-resistant infections.

Recent Development of Nanozymes for Combating Bacterial Drug Resistance: A Review

The World Health Organization has warned that without effective action, deaths from drug-resistant bacteria can exceed 10 million annually, making it the leading cause of death. Conventional antibiotics are becoming less effective due to rapid bacterial drug resistance and slowed new antibiotic development, necessitating new strategies. Recently, materials with catalytic/enzymatic properties, known as nanozymes, have been developed, inspired by natural enzymes essential for bacterial eradication. Unlike recent literature reviews that broadly cover nanozyme design and biomedical applications, this review focuses on the latest advancements in nanozymes for combating bacterial drug resistance, emphasizing their design, structural characteristics, applications in combination therapy, and future prospects. This approach aims to promote nanozyme development for combating bacterial drug resistance, especially towards clinical translation.

Synthesis and characterization of new antimicrobial peptides derived from Temporin F

Antimicrobial peptides (AMPs) are a promising source of new compounds against resistant bacteria. Temporins are a class of AMPs found on the amphibian Rana temporaria and show activity against Gram-positive and Gram-negative bacteria. There are few studies on how these antimicrobials have been used, but new Temporin-F derivatives were engineered with Lys-substitutions to assess the impact of the net charge on antimicrobial activity and toxicity. We demonstrated through some assays that it is possible to increase the antibacterial activity while maintaining a reduced peptide hemolytic activity with specific substitutions. Our lead synthetic peptide, G6K-Temporin F, has shown higher antimicrobial activity against Gram-negative and Gram-positive bacteria in vitro (MIC range 2 to 32 μmol L-1), with low hemolytic activity maintained, resulting in an increase in the therapeutic window (TW), of 12.5. Also, it showed more resistant to enzymatic degradation. On the other hand, more significant increases in net charges, such as in P3K-G11K-Temporin F, result in a severe increase in toxicity with lower gains in antimicrobial activity (TW of 0.65). In conclusion, we demonstrated that a moderate increase in net charge can lead to a more active analog and G6K-Temporin F is revealed to be promising as a candidate for new AMP therapeutics.

Evaluation of the Antibacterial Potential of Two Short Linear Peptides YI12 and FK13 against Multidrug-Resistant Bacteria

The accelerating spread of antibiotic resistance has significantly weakened the clinical efficacy of existing antibiotics, posing a severe threat to public health. There is an urgent need to develop novel antimicrobial alternatives that can bypass the mechanisms of antibiotic resistance and effectively kill multidrug-resistant (MDR) pathogens. Antimicrobial peptides (AMPs) are one of the most promising candidates to treat MDR pathogenic infections since they display broad-spectrum antimicrobial activities and are less prone to achieve drug resistance. In this study, we investigated the antibacterial capability and mechanisms of two machine learning-driven linear peptide compounds termed YI12 and FK13. We reveal that YI12 and FK13 exhibit broad-spectrum antibacterial properties against clinically significant bacterial pathogens, inducing no or minimal hemolysis in mammalian red blood cells. We further ascertain that YI12 and FK13 are resilient to heat and acid-base conditions, and exhibit susceptibility to hydrolytic enzymes and divalent cations under physiological conditions. Initial mechanistic investigations reveal that YI12 and FK13 compromise bacterial membrane integrity, leading to membrane potential dissipation and excessive reactive oxygen species (ROS) generation. Collectively, our findings highlight the prospective utility of these two cationic amphiphilic peptides as broad-spectrum antibacterial agents.

Inhalable SPRAY nanoparticles by modular peptide assemblies reverse alveolar inflammation in lethal Gram-negative bacteria infection

Current pharmacotherapy remains futile in acute alveolar inflammation induced by Gram-negative bacteria (GNB), eliciting consequent respiratory failure. The release of lipid polysaccharides after antibiotic treatment and subsequent progress of proinflammatory cascade highlights the necessity to apply effective inflammation management simultaneously. This work describes modular self-assembling peptides for rapid anti-inflammatory programming (SPRAY) to form nanoparticles targeting macrophage specifically, having anti-inflammation and bactericidal functions synchronously. SPRAY nanoparticles accelerate the self-delivery process in macrophages via lysosomal membrane permeabilization, maintaining anti-inflammatory programming in macrophages with efficacy close to T helper 2 cytokines. By pulmonary deposition, SPRAY nanoparticles effectively suppress inflammatory infiltration and promote alveoli regeneration in murine aseptic acute lung injury. Moreover, SPRAY nanoparticles efficiently eradicate multidrug-resistant GNB in alveoli by disrupting bacterial membrane. The universal molecular design of SPRAY nanoparticles provides a robust and clinically unseen local strategy in reverse acute inflammation featured by a high accumulation of proinflammatory cellularity and drug-resistant bacteria.

Reaction-Induced Self-Assembly of Polymyxin Mitigates Cytotoxicity and Reverses Drug Resistance

Polymyxins have been regarded as an efficient therapeutic against many life-threatening, multidrug resistant Gram-negative bacterial infections; however, the cytotoxicity and emergence of drug resistance associated with polymyxins have greatly hindered their clinical potential. Herein, the reaction-induced self-assembly (RISA) of polymyxins and natural aldehydes in aqueous solution is presented. The resulting assemblies effectively mask the positively charged nature of polymyxins, reducing their cytotoxicity. Moreover, the representative PMBA4 (composed of polymyxin B (PMB) and (E)-2-heptenal (A4)) assemblies demonstrate enhanced binding to Gram-negative bacterial outer membranes and exhibit multiple antimicrobial mechanisms, including increased membrane permeability, elevated bacterial metabolism, suppression of quorum sensing, reduced ATP synthesis, and potential reduction of bacterial drug resistance. Remarkably, PMBA4 assemblies reverse drug resistance in clinically isolated drug-resistant strains of Gram-negative bacteria, demonstrating exceptional efficacy in preventing and eradicating bacterial biofilms. PMBA4 assemblies efficiently eradicate Gram-negative bacterial biofilm infections in vivo and alleviate inflammatory response. This RISA strategy offers a practical and clinically applicable approach to minimize side effects, reverse drug resistance, and prevent the emergence of resistance associated with free polymyxins.

Origami of KR-12 Designed Antimicrobial Peptides and Their Potential Applications

This review describes the discovery, structure, activity, engineered constructs, and applications of KR-12, the smallest antibacterial peptide of human cathelicidin LL-37, the production of which can be induced under sunlight or by vitamin D. It is a moonlighting peptide that shows both antimicrobial and immune-regulatory effects. Compared to LL-37, KR-12 is extremely appealing due to its small size, lack of toxicity, and narrow-spectrum antimicrobial activity. Consequently, various KR-12 peptides have been engineered to tune peptide activity and stability via amino acid substitution, end capping, hybridization, conjugation, sidechain stapling, and backbone macrocyclization. We also mention recently discovered peptides KR-8 and RIK-10 that are shorter than KR-12. Nano-formulation provides an avenue to targeted delivery, controlled release, and increased bioavailability. In addition, KR-12 has been covalently immobilized on biomaterials/medical implants to prevent biofilm formation. These constructs with enhanced potency and stability are demonstrated to eradicate drug-resistant pathogens, disrupt preformed biofilms, neutralize endotoxins, and regulate host immune responses. Also highlighted are the safety and efficacy of these peptides in various topical and systemic animal models. Finaly, we summarize the achievements and discuss future developments of KR-12 peptides as cosmetic preservatives, novel antibiotics, anti-inflammatory peptides, and microbiota-restoring agents.

Synergistic collaboration between AMPs and non-direct antimicrobial cationic peptides

Non-direct antimicrobial cationic peptides (NDACPs) are components of the animal innate immune system. But their functions and association with antimicrobial peptides (AMPs) are incompletely understood. Here, we reveal a synergistic interaction between the AMP AW1 and the NDACP AW2, which are co-expressed in the frog Amolops wuyiensis. AW2 enhances the antibacterial activity of AW1 both in vitro and in vivo, while mitigating the development of bacterial resistance and eradicating biofilms. AW1 and AW2 synergistically damage bacterial membranes, facilitating cellular uptake and interaction of AW2 with the intracellular target bacterial genomic DNA. Simultaneously, they trigger the generation of ROS in bacteria, contributing to cell death upon reaching a threshold level. Moreover, we demonstrate that this synergistic antibacterial effect between AMPs and NDACPs is prevalent across diverse animal species. These findings unveil a robust and previously unknown correlation between AMPs and NDACPs as a widespread antibacterial immune defense strategy in animals.

Novel Nano Drug-Loaded Hydrogel Coatings for the Prevention and Treatment of CAUTI

Catheter-associated urinary tract infection (CAUTI) is a prevalent type of hospital-acquired infection, affecting approximately 15% to 25% of patients with urinary catheters. Long-term use of the catheter can lead to colonization of microorganisms and biofilm formation, and may develop into bacterial CAUTI. However, the frequent replacement of catheters in clinical settings can result in tissue damage, inflammation, ulceration, and additional complications, causing discomfort and pain for patients. In light of these challenges, a novel nanodrug-supported hydrogel coating called NP-AM/FK@OMV-P/H has been developed in this study. Through in vitro experiments, it is confirmed that OMV nano-loaded liquid gel coating has an effective reaction against E.coli HAase and releases antibacterial drugs. This coating has also demonstrated strong inhibition of E.coli and has shown the ability to inhibit the formation of bacterial biofilm. These findings highlight the potential of the OMV nanoparticle gel coating in preventing and treating bacterial infections. Notably, NP-AM/FK@OMV-P/H has exhibited greater efficacy against multidrug-resistant E.coli associated with UTIs compared to coatings containing single antimicrobial peptides or antibiotics. Additionally, it has demonstrated good biosecurity. In conclusion, the NP-AM/FK@OMV-P/H coating holds great potential in providing benefits to patients with CAUTI.

Farnesol Emulsion as an Effective Broad-Spectrum Agent against ESKAPE Biofilms

The family of ESKAPE pathogens is comprised of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter. Together they are the main contributors of nosocomial infections and are well established for their ability to "escape" antibiotics. Farnesol is an FDA-approved cosmetic and flavoring agent with significant anti-biofilm properties. In a proprietary emulsion, farnesol has been shown to be capable of disrupting S. aureus, P. aeruginosa, and A. baumannii biofilms. The current work demonstrates that this farnesol emulsion reduces the number of viable bacteria, while also leading to reductions in biomass, of the other three ESKAPE pathogens: Enterococcus faecium, Klebsiella pneumoniae, and Enterobacter, both in vitro and in an ex vivo human skin model. A concentration of 0.5 mg/mL was effective for impeding biofilm development of all three bacteria, while 1 mg/mL for E. faecium and K. pneumoniae, or 0.2 mg/mL for E. cloacae, was able to kill bacteria in established biofilms. Contrary to antibiotics, no resistance to farnesol was observed for E. faecium or K. pneumoniae. The results indicate that farnesol is effective for direct cell killing and also has the ability to induce biofilm detachment from surfaces, as confirmed using Live/Dead image analysis. Our findings confirm that farnesol emulsion is an effective broad-spectrum agent to impede ESKAPE biofilms.

Peptide-based strategies for overcoming biofilm-associated infections: a comprehensive review

Biofilms represent resilient microbial communities responsible for inducing chronic infections in human subjects. Given the escalating challenges associated with antibiotic therapy failures in clinical infections linked to biofilm formation, a peptide-based approach emerges as a promising alternative to effectively combat these notoriously resistant biofilms. Contrary to conventional antimicrobial peptides, which predominantly target cellular membranes, antibiofilm peptides necessitate a multifaceted approach, addressing various "biofilm-specific factors." These factors encompass Extracellular Polymeric Substance (EPS) degradation, membrane targeting, cell signaling, and regulatory mechanisms. Recent research endeavors have been directed toward assessing the potential of peptides as potent antibiofilm agents. However, to translate these peptides into viable clinical applications, several critical considerations must be meticulously evaluated during the peptide design process. This review serves to furnish an all-encompassing summary of the pivotal factors and parameters that necessitate contemplation for the successful development of an efficacious antibiofilm peptide.

The structural characterization and UV-protective properties of an exopolysaccharide from a Paenibacillus isolate

Introduction

Overexposure to ultraviolet (UV) light is known to cause damage to the skin, leading to sunburn and photo-aging. Chemical sunscreen products may give rise to health risks including phototoxicity, photosensitivity, and photosensitivity. Natural polysaccharides have attracted considerable interests due to diverse biological activities.

Methods

A novel polysaccharide isolated was purified and structurally characterized using chemical methods followed by HPLC, GLC-MS, as well as 1D and 2D NMR spectroscopy. The photoprotective effect of the EPS on UVB-induced damage was assessed in vitro using cultured keratinocytes and in vivo using C57BL/6 mouse models.

Results

The average molecular weight of the EPS was 5.48 × 106 Da, composed of glucose, mannose and galactose residues at a ratio of 2:2:1. The repeating units of the EPS were →3)-β-D-Glcp (1→3) [β-D-Galp (1→2)-α-D-Glcp (1→2)]-α-D-Manp (1→3)-α-D-Manp (1→. In cultured keratinocytes, the EPS reduced cytotoxicity and excessive ROS production induced by UVB irradiation. The EPS also exhibits an inhibitory effect on oxidative stress, inflammation, and collagen degradation found in the photodamage in mice. 1H NMR-based metabolomics analysis for skin suggested that the EPS partly reversed the shifts of metabolic profiles of the skin in UVB-exposed mice.

Conclusion

The EPS exhibits skin photoprotective effects through regulating oxidative stress both in vivo and in vitro. Our findings highlight that the EPS is a potential candidate in sunscreen formulations for an efficient solution to UVB radiation.

Engineered Probiotic Bio-Heterojunction with Robust Antibiofilm Modality via "Eating" Extracellular Polymeric Substances for Wound Regeneration

The compact three-dimensional (3D) structure of extracellular polymeric substances (EPS) within biofilms significantly hinders the penetration of antimicrobial agents, making biofilm eradication challenging and resulting in persistent biofilm-associated infections. To address this challenge, a solution is proposed: a probiotic bio-heterojunction (P-bioHJ) combining Lactobacillus rhamnosus with MXene (Ti3C2) quantum dots (MQDs)/FeS heterojunction. This innovation aims to break down the saccharides in EPS, enabling effective combat against biofilm-associated infections. Initially, the P-bioHJ targets saccharides through metabolic processes, causing the collapse of EPS and allowing infiltration into bacterial colonies. Simultaneously, upon exposure to near-infrared (NIR) irradiation, the P-bioHJ produces reactive oxygen species (ROS) and thermal energy, deploying physical mechanisms to combat bacterial biofilms effectively. Following antibiofilm treatment, the P-bioHJ adjusts the oxidative environment, reduces wound inflammation by scavenging ROS, boosts antioxidant enzyme activity, and mitigates the NF-κB inflammatory pathway, thereby accelerating wound healing. In vitro and in vivo experiments confirm the exceptional antibiofilm, antioxidant/anti-inflammatory, and wound-regeneration properties of P-bioHJ. In conclusion, this study provides a promising approach for treating biofilm-related infections.

Activity and mechanism of action of antimicrobial peptide ACPs against Candida albicans

AIMS

Candida albicans is the most prevalent pathogenic fungus, exhibiting escalating multidrug resistance (MDR). Antimicrobial peptides (AMPs) represent promising candidates for addressing this issue. In this research, five antimicrobial peptides, ACP1 to ACP5 which named ACPs were studied as alternative fungicidal molecules.

MAIN METHODS

CD assay was used to analyze the 2D structures, Absorbance method was used to test the antimicrobial activity, haemolytic activity, time-kill kinetics, biofilm inhibition and reduction activity, resistance induction activity and assessment against fluconazole-resistant C. albicans. SEM, TEM, CLSM, flow cytometer and FM were carried out to provide insight into the mechanisms of anti-Candida action.

KEY FINDINGS

ACPs possessed an α-helical structure and strong anti-Candida activities, with minimum inhibitory concentrations (MICs) from 3.9 to 15.6 μg/mL. In addition, ACPs did not produce hemolysis at concentrations lower than 10 or 62 × MIC, indicating their low cytotoxicity. Fungicidal kinetics showed that they completely killed C. albicans within 8 h at 2 to 4 × MIC. Notably, ACPs were highly fungicidal against fluconazole-resistant C. albicans and showed low resistance. In addition, they were effective in inhibiting mycelium and biofilm formation. Fluorescence microscopy revealed that while fluconazole had minimal to no inhibitory effect on biofilm-forming cells, ACPs induced apoptosis in all of them. The research on mechanism of action revealed that ACPs disrupted the cell membranes, with ROS increasing and cellular mitochondrial membrane potential decreasing.

SIGNIFICANCE

ACPs could be promising candidates for combating fluconazole-resistant C. albicans infections.

TC-14, a cathelicidin-derived antimicrobial peptide with broad-spectrum antibacterial activity and high safety profile

Cathelicidins, a major class of antimicrobial peptides (AMPs), hold considerable potential for antimicrobial drug development. In the present study, we identified a novel cathelicidin AMP (TC-33) derived from the Chinese tree shrew. Despite TC-33 demonstrating weak antimicrobial activity, the novel peptide TC-14, developed based on its active region, exhibited a 432-fold increase in antimicrobial activity over the parent peptide. Structural analysis revealed that TC-14 adopted an amphipathic α-helical conformation. The bactericidal mechanism of TC-14 involved targeting and disrupting the bacterial membrane, leading to rapid membrane permeabilization and rupture. Furthermore, TC-14 exhibited a high-safety profile, as evidenced by the absence of cytotoxic and hemolytic activities, as well as high biocompatibility and safety in vivo. Of note, its potent antimicrobial activity provided significant protection in a murine model of skin infection. Overall, this study presents TC-14 as a promising drug candidate for antimicrobial drug development.

Antibacterial activity and mechanism of luteolin isolated from Lophatherum gracile Brongn. against multidrug-resistant Escherichia coli

Infections caused by multidrug-resistant (MDR) bacteria have become a major challenge for global healthcare systems. The search for antibacterial compounds from plants has received increasing attention in the fight against MDR bacteria. As a medicinal and edible plant, Lophatherum gracile Brongn. (L. gracile) has favorable antibacterial effect. However, the main antibacterial active compound and its antimicrobial mechanism are not clear. Here, our study first identified the key active compound from L. gracile as luteolin. Meanwhile, the antibacterial effect of luteolin was detected by using the broth microdilution method and time-kill curve analysis. Luteolin can also cause morphological structure degeneration and content leakage, cell wall/membrane damage, ATP synthesis reduction, and downregulation of mRNA expression levels of sulfonamide and quinolones resistance genes in multidrug-resistant Escherichia coli (MDR E. coli). Furthermore, untargeted UPLC/Q-TOF-MS-based metabolomics analysis of the bacterial metabolites revealed that luteolin significantly changed riboflavin energy metabolism, bacterial chemotaxis cell process and glycerophospholipid metabolism of MDR E. coli. This study suggests that luteolin could be a potential new food additive or preservative for controlling MDR E. coli infection and spread.

Farnesol repurposing for prevention and treatment of Acinetobacter baumannii biofilms

Acinetobacter baumannii has emerged as a multidrug-resistant (MDR) superbug by causing severe infections, with high mortality rates. The ability of A. baumannii to form biofilms significantly contributes to its persistence in diverse environmental and hospital settings. Here we report that farnesol, an FDA-approved commercial cosmetic and flavoring agent, demonstrates efficacy for both inhibition of biofilm formation, and disruption of established A. baumannii biofilms. Moreover, no resistance to farnesol was observed even after prolonged culture in the presence of sub-inhibitory farnesol doses. Farnesol combats A. baumannii biofilms by direct killing, while also facilitating biofilm detachment. Furthermore, farnesol was safe, and effective, for both prevention and treatment of A. baumannii biofilms in an ex vivo burned human skin model. Since current treatment options for A. baumannii biofilm infections were mainly counted on the combination therapy of last-resort antibiotics, and clearly non-sustainable due to robust MDR phenotype of A. baumannii, we propose that farnesol alone can be repurposed as a highly effective agent for both preventing and treating life-threating biofilm-associated infections of A. baumannii due to its proven safety, convenient topical delivery, and excellent efficiency, plus its superiority of evading resistance development.

Milk-derived extracellular vesicles functionalized with anti-tumour necrosis factor-α nanobody and anti-microbial peptide alleviate ulcerative colitis in mice

Ulcerative colitis (UC) manifests clinically with chronic intestinal inflammation and microflora dysbiosis. Although biologics can effectively control inflammation, efficient delivery to the colon and colon epithelial cells remains challenging. Milk-derived extracellular vesicles (EV) show promise as an oral delivery tool, however, the ability to load biologics into EV presents challenges to therapeutic applications. Here, we demonstrate that fusing cell-penetrating peptide (TAT) to green fluorescent protein (GFP) enabled biologics loading into EV and protected against degradation in the gastrointestinal environment in vitro and in vivo after oral delivery. Oral administration of EV loaded with anti-tumour necrosis factor-α (TNF-α) nanobody (VHHm3F) (EVVHH) via TAT significantly reduced tissue TNF-α levels and alleviated pathologies in mice with acute UC, compared to VHH alone. In mice with chronic UC, simultaneously introducing VHH and an antimicrobial peptide LL37 into EV (EVLV), then administering orally improved intestinal barrier, inflammation and microbiota balance, resulted in relief of UC-induced depression and anxiety. Collectively, we demonstrated that oral delivery of EVLV effectively alleviated UC in mice and TAT efficiently loaded biologics into EV to confer protection from degradation in the gastrointestinal tract. This therapeutic strategy is promising for UC and is a simple and generalizable approach towards drug-loaded orally-administrable EV treatment for other diseases.

New-generation biofilm effective antimicrobial peptides and a real-time anti-biofilm activity assay: CoMIC

Nowadays, it is very important to produce new-generation drugs with antimicrobial properties that will target biofilm-induced infections. The first target for combating these microorganisms, which are the source itself. Antimicrobial peptides, which are more effective than antibiotics due to their ability to kill microorganisms and use a different metabolic pathway, are among the new options today. The aim of this study is to develop new-generation antibiotics that inhibit both biofilm-producing bacteria and the biofilm itself. For this purpose, we designed four different peptides by combining two amino acid forms (D- and L-) with the same sequence having alpha helix structures. It was found that the combined use of these two forms can increase antimicrobial efficacy more than 30-fold. These results are supported by molecular modeling and scanning electron microscopy (SEM), at the same time cytotoxicity (IC50) and hemotoxicity (HC50) values remained within the safe range. Furthermore, antibiofilm activities of these peptides were investigated. Since the existing biofilm inhibition methods in the literature do not technically simulate the exact situation, in this study, we have developed a real-time observable biofilm model and a new detection method based on it, which we call the CoMIC method. Findings have shown that the NET1 peptide with D-leucine amino acid in its structure and the NET3 peptide with D-arginine amino acid in its structure are effective in inhibiting biofilm. As a conclusion, our peptides can be considered as potential next-generation broad-spectrum antibiotic molecule/drug candidates that might be used in biofilm and clinical important bacteria. KEY POINTS: • Antimicrobial peptides were developed to inhibit both biofilms producing bacteria and the biofilm itself. • CoMIC will fill a very crucial gap in understanding biofilms and conducting the necessary quantitative studies. • Molecular modelling studies, NET1 peptide molecules tends to move towards and adhere to the membrane within nanoseconds.

Design of a Novel Lysine Isopeptide 1018KI11 with Potent Antimicrobial Activity as a Safe and Stable Food Preservative Candidate

Antimicrobial peptides are potent food additive candidates, but most of them are sensitive to proteases, which limits their application. Therefore, we substituted arginine for lysine and introduced a lysine isopeptide bond to peptide IDR-1018 in order to improve its enzymatic stability. Subsequently, the protease stability and antimicrobial/antibiofilm activity of the novel peptides (1018K2-1018KI11) were investigated. The data revealed that the antienzymatic potential of 1018KI11 to bromelain and papain increased by 2-8 folds and 16 folds, respectively. The minimum inhibitory concentration (MIC) of 1018KI11 against methicillin-resistant Staphylococcus aureus (MRSA) ATCC43300 and Escherichia coli (E. coli) ATCC25922 was reduced 2-fold compared to 1018K11. Mechanism exploration suggested that 1018KI11 was more effective than 1018K11 in disrupting the cell barrier and damaging genomic DNA. Additionally, 1018KI11 at certain concentration conditions (2-64 μg/mL) reduced biofilm development of MRSA ATCC43300 by 4.9-85.9%. These data indicated that novel peptide 1018KI11 is a potential food preservative candidate.

AMPpred-MFA: An Interpretable Antimicrobial Peptide Predictor with a Stacking Architecture, Multiple Features, and Multihead Attention

Antimicrobial peptides (AMPs) are small molecular polypeptides that can be widely used in the prevention and treatment of microbial infections. Although many computational models have been proposed to help identify AMPs, a high-performance and interpretable model is still lacking. In this study, new benchmark data sets are collected and processed, and a stacking deep architecture named AMPpred-MFA is carefully designed to discover and identify AMPs. Multiple features and a multihead attention mechanism are utilized on the basis of a bidirectional long short-term memory (LSTM) network and a convolutional neural network (CNN). The effectiveness of AMPpred-MFA is verified through five independent tests conducted in batches. Experimental results show that AMPpred-MFA achieves a state-of-the-art performance. The visualization interpretability analyses and ablation experiments offer a further understanding of the model behavior and performance, validating the importance of our feature representation and stacking architecture, especially the multihead attention mechanism. Therefore, AMPpred-MFA can be considered a reliable and efficient approach to understanding and predicting AMPs.

Host defense peptides mitigate the spread of antibiotic resistance in physiologically relevant condition

Antibiotic resistance represents a significant challenge to public health and human safety. The primary driver behind the dissemination of antibiotic resistance is the horizontal transfer of plasmids. Current conjugative transfer assay is generally performed in a standardized manner, ignoring the effect of the host environment. Host defense peptides (HDPs) possess a wide range of biological targets and play an essential role in the innate immune system. Herein, we reveal that sub-minimum inhibitory concentrations of HDPs facilitate the conjugative transfer of RP4-7 plasmid in the Luria Broth medium, and this observation is reversed in the RPMI medium, designed to simulate the host environment. Out of these HDPs, indolicidin (Ind), a cationic tridecapeptide from bovine neutrophils, significantly inhibits the conjugation of multidrug resistance plasmids in a dose-dependent manner, including blaNDM- and tet(X4)-bearing plasmids. We demonstrate that the addition of Ind to RPMI medium as the incubation substrate downregulates the expression of conjugation-related genes. In addition, Ind weakens the tricarboxylic acid cycle, impedes the electron transport chain, and disrupts the proton motive force, consequently diminishing the synthesis of adenosine triphosphate and limiting the energy supply. Our findings highlight the importance of the host-like environments for the development of horizontal transfer inhibitors and demonstrate the potential of HDPs in preventing the spread of resistance plasmids.

Antimicrobial peptide DvAMP combats carbapenem-resistant Acinetobacter baumannii infection

Carbapenem-resistant Acinetobacter baumannii (CRAB), an important opportunistic pathogen, is a major cause of healthcare-associated infections. The polymyxins (colistin and polymyxin B) are the last line of defense in the treatment of CRAB infections, and there is an urgent need to develop novel alternative therapeutic strategies. In this study, we found that the antimicrobial peptide DvAMP exhibited satisfactory antibacterial and antibiofilm activity against CRAB. In addition, DvAMP showed tolerable stability in salt ions and serum and exhibited low toxicity in vivo. Investigation of the underlying mechanism demonstrated that DvAMP disrupts cell membrane structural integrity and specifically binds to exogenous lipopolysaccharides (LPS) and phospholipids (PG/CL), resulting in increased membrane permeability and dissipating proton motive force (PMF), further reducing intracellular ATP levels and inducing ROS accumulation, leading to bacterial death. Furthermore, DvAMP therapy efficiently improved survival rates and decreased the bacterial load in the lungs of mice in a mouse pneumonia model, showing that DvAMP administration reduced CRAB susceptibility to lung infection. These results indicate that the peptide DvAMP is a promising alternative therapeutic agent to combat CRAB infection.

Developments and Trends of Nanotechnology Application in Sepsis: A Comprehensive Review Based on Knowledge Visualization Analysis

Sepsis, a common life-threatening clinical condition, continues to have high morbidity and mortality rates, despite advancements in management. In response, significant research efforts have been directed toward developing effective strategies. Within this scope, nanotechnology has emerged as a particularly promising field, attracting significant interest for its potential to enhance disease diagnosis and treatment. While several reviews have highlighted the use of nanoparticles in sepsis, comprehensive studies that summarize and analyze the hotspots and research trends are lacking. To identify and further promote the development of nanotechnology in sepsis, a bibliometric analysis was conducted on the relevant literature, assessing research trends and hotspots in the application of nanomaterials for sepsis. Next, a comprehensive review of the subjectively recognized research hotspots in sepsis, including nanotechnology-enhanced biosensors and nanoscale imaging for sepsis diagnostics, and nanoplatforms designed for antimicrobial, immunomodulatory, and detoxification strategies in sepsis therapy, is elucidated, while the potential side effects and toxicity risks of these nanomaterials were discussed. Particular attention is given to biomimetic nanoparticles, which mimic the biological functions of source cells like erythrocytes, immune cells, and platelets to evade immune responses and effectively deliver therapeutic agents, demonstrating substantial translational potential. Finally, current challenges and future perspectives of nanotechnology applications in sepsis with a view to maximizing their great potential in the research of translational medicine are also discussed.

Rational Design of a Potent Antimicrobial Peptide Based on the Active Region of a Gecko Cathelicidin

The emergence of multidrug-resistant (MDR) bacteria presents a significant challenge to public health, increasing the risk of infections that are resistant to current antibiotic treatment. Antimicrobial peptides (AMPs) offer a promising alternative to conventional antibiotics in the prevention of MDR bacterial infections. In the present study, we identified a novel cathelicidin AMP from Gekko japonicus, which exhibited broad-spectrum antibacterial activity against both Gram-negative and Gram-positive bacteria, with minimal inhibitory concentrations ranging from 2.34 to 4.69 μg/mL. To improve its potential therapeutic application, a series of peptides was synthesized based on the active region of the gecko-derived cathelicidin. The lead peptide (RH-16) showed an antimicrobial activity comparable to that of the parent peptide. Structural characterization revealed that RH-16 adopted an amphipathic α-helical conformation. Furthermore, RH-16 demonstrated neither hemolytic nor cytotoxic activity but effectively killed a wide range of clinically isolated, drug-resistant bacteria. The antimicrobial activity of RH-16 was attributed to the nonspecific targeting of bacterial membranes, leading to rapid bacterial membrane permeabilization and rupture. RH-16 also retained its antibacterial activity in plasma and exhibited mild toxicity in vivo. Notably, RH-16 offered robust protection against skin infection in a murine model. Therefore, this newly identified cathelicidin AMP may be a strong candidate for future pharmacological development targeting multidrug resistance. The use of a rational design approach for isolating the minimal antimicrobial unit may accelerate the transition of natural AMPs to clinically applicable antibacterial agents.

Effective ciprofloxacin cationic antibacterial agent against persister bacteria with low hemolytic toxicity

With the widespread use of antibiotics, bacterial resistance has developed rapidly. To make matters worse, infections caused by persistent bacteria and biofilms often cannot be completely eliminated, which brings great difficulties to clinical medication. In this work, three series of quinolone pyridinium quaternary ammonium small molecules were designed and synthesized. Most of the compounds showed good antibacterial activity against Gram-positive bacteria (S. aureus and E. faecalis) and Gram-negative bacteria (E. coli and S. maltophilia). The activity of the para-pyridine quaternary ammonium salt was better than that of the meta-pyridine. 3f was the optimal compound with good stability in body fluids and was unlikely to induce bacterial resistance. The hemolysis rate of erythrocytes at 1280 μg/mL for 3f was only 5.1%. Encouragingly, 3f rapidly killed bacteria within 4 h at 4 × MIC concentration and was effective in killing persistent bacteria in biofilms. The antibacterial mechanism experiments showed that 3f could cause disorder of bacterial membrane potential, increase bacterial membrane permeability, dissolve and destroy the membrane. Incomplete bacterial membranes lead to leakage of bacterial genetic material, concomitant production of ROS, and bacterial death due to these multiple effects.

Anti-Staphylococcus aureus effects of natural antimicrobial peptides and the underlying mechanisms

Staphylococcus aureus can cause localized infections such as abscesses and pneumonia, as well as systemic infections such as bacteremia and sepsis. Especially, methicillin-resistant S. aureus often presents multidrug resistance, which becomes a major clinical challenge. One of the most common reasons for methicillin-resistant S. aureus antibiotic resistance is the presence of biofilms. Natural antimicrobial peptides derived from different species have shown effectiveness in combating S. aureus biofilms. In this review, we summarize the inhibitory activity of antimicrobial peptides against S. aureus planktonic cells and biofilms. We also summarize the possible inhibitory mechanisms, involving cell adhesion inhibition, membrane fracture, biofilm disruption and DNA disruption. We believe this can provide the basis for further research against S. aureus biofilm-associated infections.

Identification of Genes Associated with Resistance to Persulcatusin, a Tick Defensin from Ixodes persulcatus

Antimicrobial peptides (AMPs) are present in a wide range of plants, animals, and microorganisms. Since AMPs are characterized by their effectiveness against emergent antibiotic-resistant bacteria, they are attracting attention as next-generation antimicrobial compounds that could solve the problem of drug-resistant bacteria. Persulcatusin (IP), an antibacterial peptide derived from the hard tick Ixodes persulcatus, shows high antibacterial activity against various Gram- positive bacteria as well as multidrug-resistant bacteria. However, reports on the antibacterial action and resistance mechanisms of IP are scarce. In this study, we spontaneously generated mutants showing increased a minimum inhibitory concentration (MIC) of IP and analyzed their cross-resistance to other AMPs and antibiotics. We also used fluorescent probes to investigate the target of IP activity by evaluating IP-induced damage to the bacterial cytoplasmic membrane. Our findings suggest that the antimicrobial activity of IP on bacterial cytoplasmic membranes occurs via a mechanism of action different from that of known AMPs. Furthermore, we screened for mutants with high susceptibility to IP using a transposon mutant library and identified 16 genes involved in IP resistance. Our results indicate that IP, like other AMPs, depolarizes the bacterial cytoplasmic membrane, but it may also alter membrane structure and inhibit cell-wall synthesis.

Optimization of sequence and chiral content enhances therapeutic potential of tilapia piscidin peptides

Because antimicrobial peptides (AMPs) often exhibit broad-spectrum bactericidal potency, we sought to develop peptide-based antimicrobials for potential clinical use against drug-resistant pathogens. To accomplish this goal, we first optimized the amino acid sequence of a broad-spectrum AMP known as Tilapia Piscidin 4 (TP4). Then, we used the optimized sequence to create a pair of heterochiral variants (TP4-α and TP4-β) with different percentages of D-enantiomers, as poly-L peptides often exhibit poor pharmacokinetic profiles. The conformations of the peptide pair exhibited inverted chirality according to CD and NMR spectroscopic analyses. Both heterochiral peptides displayed enhanced stability and low hemolysis activities. Irrespective of their different d-enantiomer contents, both heterochiral peptides exhibited bactericidal activities in the presence of human serum or physiological enzymes. However, the peptide with higher d-amino acid content (TP4-β) caused better bacterial clearance when tested in mice infected with NDM-1 K. pneumoniae. In addition, we observed a relatively higher hydrogen bonding affinity in a simulation of the interaction between TP4-β and a model bacterial membrane. In sum, our results demonstrate that the current design strategy may be applicable for development of new molecules with enhanced stability and in vivo antimicrobial activity.

Efficacy of the bee-venom antimicrobial peptide Osmin against sensitive and carbapenem-resistant Klebsiella pneumoniae strains

The emergence of multidrug-resistant (MDR) Klebsiella pneumoniae strains causes severe problems in the treatment of bacterial infections owing to limited treatment options. Especially, carbapenem-resistant Klebsiella pneumoniae (CRKP) is rapidly spreading worldwide and is emerging as a new cause of drug-resistant healthcare-associated infections. CRKP also has been announced by the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) as one of the most pressing antibiotic resistance threats. Antimicrobial peptides (AMPs) are drawing considerable attention as ideal antibiotic alternative candidates to combat MDR bacterial infections. In a previous study, Osmin is composed of 17 amino acids and is isolated from solitary bee (Osmia rufa) venom. Herein, we evaluated the potential of Osmin to be used against drug-resistant K. pneumoniae as an alternative to conventional antibiotics. Osmin exhibited significant antimicrobial and anti-biofilm activity and lower toxicity than melittin, a well-known bee venom peptide. Additionally, we confirmed that it possesses a bactericidal mechanism that rapidly destroys bacterial membranes. Osmin was relatively more stable than melittin under the influence of various environmental factors and unlike conventional antibiotics, it exhibited a low bacterial resistance risk. During in vivo tests, Osmin reduced bacterial growth and the expression of pro-inflammatory cytokines and fibrosis-related genes in mice with CRKP-induced sepsis. Overall, our results indicate a high potential for Osmin to be used as a valuable therapeutic agent against drug-resistant K. pneumoniae infections.

Defensins: A novel weapon against Mycobacterium tuberculosis?

Tuberculosis (TB) is a serious airborne communicable disease caused by organisms of the Mycobacterium tuberculosis (Mtb) complex. Although the standard treatment antimicrobials, including isoniazid, rifampicin, pyrazinamide, and ethambutol, have made great progress in the treatment of TB, problems including the rising incidence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB), the severe toxicity and side effects of antimicrobials, and the low immunity of TB patients have become the bottlenecks of the current TB treatments. Therefore, both safe and effective new strategies to prevent and treat TB have become a top priority. As a subfamily of cationic antimicrobial peptides, defensins are rich in cysteine and play a vital role in resisting the invasion of microorganisms and regulating the immune response. Inspired by studies on the roles of defensins in host defence, we describe their research history and then review their structural features and antimicrobial mechanisms, specifically for fighting Mtb in detail. Finally, we discuss the clinical relevance, therapeutic potential, and potential challenges of defensins in anti-TB therapy. We further debate the possible solutions of the current application of defensins to provide new insights for eliminating Mtb.

Novel antimicrobial peptides modified with fluorinated sulfono-γ-AA having high stability and targeting multidrug-resistant bacteria infections

The emergence and increasing prevalence of multidrug-resistant (MDR) bacteria have posed an urgent demand for novel antibacterial drugs. Currently, antimicrobial peptides (AMPs), potential novel antimicrobial agents with rare antimicrobial resistance, represent an available strategy to combat MDR bacterial infections but suffer the limitation of protease degradation. In this study, we developed a highly effective method for optimizing the stability of AMPs by introducing fluorinated sulfono-γ-AApeptides, and successfully synthesized novel Feleucin-K3-analogs. The results demonstrated that the incorporation of fluorinated sulfono-γ-AA into Feleucin-K3 effectively improved stability and afforded optimal peptides, such as CF3-K11, which exhibited 8-9 times longer half-lives than Feleucin-K3. Moreover, CF3-K11 displayed potent antimicrobial activity against clinically isolated Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), excellent biosafety, low resistance propensity, and possessed powerful antimicrobial efficacy for both local skin infection and pneumonia infection. The optimal CF3-K11 exhibited strong therapeutic potential and offered a superior approach for treating MDR bacterial infections.

Eradication of community-onset Methicillin-resistant Staphylococcus aureus carriage: a narrative review

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) colonization increases infection risk in both patients and healthy individuals. Decolonization therapy has been proven to reduce S. aureus infections, but data on the effectiveness of individual decolonization strategies in community-onset MRSA carriage are scarce.

OBJECTIVES

The aim of this narrative review was to summarize the evidence on strategies for the elimination of MRSA colonization in community-onset MRSA carriers.

SOURCES

PubMed database was searched for studies on MRSA eradication, from inception to July 2023.

CONTENT

Topical therapy is proven to be effective in nasal-only carriage and in temporary load reduction. Mupirocin nasal ointment in combination with chlorhexidine body wash is highly effective in nasal-only MRSA carriers in the community as well. In patients with extra-nasal colonization, addition of orally administered antibiotics likely increases success rates compared with topical therapy alone. Studies on systemic treatment of extra-nasal MRSA decolonization are subject to a high heterogeneity of antimicrobial agents, treatment duration, and control groups. The majority of evidence supports the use of a combination of topical therapy with rifampin and another antimicrobial agent. Decolonization treatment with probiotics is a promising novel non-antibiotic strategy. However, achieving long-term decolonization is more likely in countries with low MRSA prevalence, given the risk of recolonization in a context of high MRSA prevalence.

IMPLICATIONS

The decision to pursue community-onset MRSA eradication treatment in the individual patient should be based on the combination of the treatment objective (short-term bacterial load reduction in health care settings vs. long-term eradication in community settings), and the likelihood of successful decolonization. The latter is influenced by both individual risk factors for treatment failure, and the risk of recolonization. The addition of a combination of systemic antibiotics is rational for extra-nasal long-term decolonization. To determine the most effective systemic antimicrobial agents in MRSA decolonization, more research is needed.

Design and synthesis of etrasimod derivatives as potent antibacterial agents against Gram-positive bacteria

The emergence of multidrug-resistant bacteria along with a declining pipeline of clinically useful antibiotics has led to the urgent need for the development of more effective antibacterial agents. Inspired by our recent report on the antibacterial activity of etrasimod, an immunomodulating drug candidate, we prepared a series of etrasimod derivatives by varying substituents on the phenyl ring, altering the central tricyclic aromatic ring, and modifying the carboxyl group. From this series of compounds, indole derivative 24f was identified as the most potent antibacterial compound, with the minimum inhibitory concentration (MIC) values between 2.5 and 10 μM against various Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), S. epidermidis and enterococci. Moreover, 24f exhibited rapid bactericidal activity against S. aureus, low toxicity and hemolytic activity, and a synergistic effect with gentamicin against S. aureus, MRSA, and Enterococcus faecalis. Furthermore, it was shown that neither etrasimod nor 24f affects S. aureus cell membranes. Importantly, 24f did not induce resistance in S. aureus, representing a significant improvement compared to etrasimod. Finally, the antibacterial activity of etrasimod and 24f against S. aureus and MRSA was confirmed in vivo in a Caenorhabditis elegans infection model. Taken together, our study highlights the value of etrasimod and its derivatives as potential antibacterial candidates for combating infections caused by Gram-positive bacteria.

Turning cationic antimicrobial peptide KR-12 into self-assembled nanobiotics with potent bacterial killing and LPS neutralizing activities

Gram-negative sepsis has become a substantial and escalating global healthcare challenge due to the growing antibiotic resistance crisis and the sluggish development of new antibiotics. LL-37, a unique Cathelicidin species found in humans, exhibits a wide range of bioactive properties, including direct bactericidal effects, inflammation regulation, and LPS neutralization. KR-12, the smallest yet potent peptide fragment of LL-37, has been modified to create more effective antimicrobials. In this study, we designed two myristoylated derivatives of KR-12, referred to as Myr-KR-12N and Myr-KR-12C. These derivatives displayed remarkable ability to spontaneously assemble into nanoparticles when mixed with deionized water. Myristoylated KR-12 derivatives exhibited broad-spectrum and intensified bactericidal activity by disrupting bacterial cell membranes. In particular, Myr-KR-12N showed superior capability to rescue mice from lethal E. coli-induced sepsis in comparison with the conventional antibiotic meropenem. We also confirmed that the myristoylated KR-12 nanobiotic possesses significant LPS binding capacity and effectively reduces inflammation in vitro. In an in vivo context, Myr-KR-12N outperformed polymyxin B in rescuing mice from LPS-induced sepsis. Crucially, toxicological assessments revealed that neither Myr-KR-12N nor Myr-KR-12C nanobiotics induced meaningful hemolysis or caused damage to the liver and kidneys. Collectively, our study has yielded an innovative nanobiotic with dual capabilities of bactericidal action and LPS-neutralization, offering substantial promise for advancing the clinical translation of antimicrobial peptides and the development of novel antibiotics. This addresses the critical need for effective solutions to combat Gram-negative sepsis, a pressing global medical challenge.

Metal-Organic Frameworks and Their Composites for Chronic Wound Healing: From Bench to Bedside

Chronic wounds are characterized by delayed and dysregulated healing processes. As such, they have emerged as an increasingly significant threat. The associated morbidity and socioeconomic toll are clinically and financially challenging, necessitating novel approaches in the management of chronic wounds. Metal-organic frameworks (MOFs) are an innovative type of porous coordination polymers, with low toxicity and high eco-friendliness. Documented anti-bacterial effects and pro-angiogenic activity predestine these nanomaterials as promising systems for the treatment of chronic wounds. In this context, the therapeutic applicability and efficacy of MOFs remain to be elucidated. It is, therefore, reviewed the structural-functional properties of MOFs and their composite materials and discusses how their multifunctionality and customizability can be leveraged as a clinical therapy for chronic wounds.

GATR-3, a Peptide That Eradicates Preformed Biofilms of Multidrug-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a gram-negative bacterium that causes hospital-acquired and opportunistic infections, resulting in pneumonia, sepsis, and severe wound infections that can be difficult to treat due to antimicrobial resistance and the formation of biofilms. There is an urgent need to develop novel antimicrobials to tackle the rapid increase in antimicrobial resistance, and antimicrobial peptides (AMPs) represent an additional class of potential agents with direct antimicrobial and/or host-defense activating activities. In this study, we present GATR-3, a synthetic, designed AMP that was modified from a cryptic peptide discovered in American alligator, as our lead peptide to target multidrug-resistant (MDR) A. baumannii. Antimicrobial susceptibility testing and antibiofilm assays were performed to assess GATR-3 against a panel of 8 MDR A. baumannii strains, including AB5075 and some clinical strains. The GATR-3 mechanism of action was determined to be via loss of membrane integrity as measured by DiSC3(5) and ethidium bromide assays. GATR-3 exhibited potent antimicrobial activity against all tested multidrug-resistant A. baumannii strains with rapid killing. Biofilms are difficult to treat and eradicate. Excitingly, GATR-3 inhibited biofilm formation and, more importantly, eradicated preformed biofilms of MDR A. baumannii AB5075, as evidenced by MBEC assays and scanning electron micrographs. GATR3 did not induce resistance in MDR A. baumannii, unlike colistin. Additionally, the toxicity of GATR-3 was evaluated using human red blood cells, HepG2 cells, and waxworms using hemolysis and MTT assays. GATR-3 demonstrated little to no cytotoxicity against HepG2 and red blood cells, even at 100 μg/mL. GATR-3 injection showed little toxicity in the waxworm model, resulting in a 90% survival rate. The therapeutic index of GATR-3 was estimated (based on the HC50/MIC against human RBCs) to be 1250. Overall, GATR-3 is a promising candidate to advance to preclinical testing to potentially treat MDR A. baumannii infections.

Repurposing of the antimalarial agent tafenoquine to combat MRSA

IMPORTANCE

This study represents the first investigation into the antimicrobial effect of TAF against S. aureus and its potential mechanisms. Our data highlighted the effects of TAF against MRSA planktonic cells, biofilms, and persister cells, which is conducive to broadening the application of TAF. Through mechanistic studies, we revealed that TAF targets bacterial cell membranes. In addition, the in vivo experiments in mice demonstrated the safety and antimicrobial efficacy of TAF, suggesting that TAF could be a potential antibacterial drug candidate for the treatment of infections caused by multiple drug-resistant S. aureus.

Biofilm antimicrobial susceptibility testing: where are we and where could we be going?

Our knowledge about the fundamental aspects of biofilm biology, including the mechanisms behind the reduced antimicrobial susceptibility of biofilms, has increased drastically over the last decades. However, this knowledge has so far not been translated into major changes in clinical practice. While the biofilm concept is increasingly on the radar of clinical microbiologists, physicians, and healthcare professionals in general, the standardized tools to study biofilms in the clinical microbiology laboratory are still lacking; one area in which this is particularly obvious is that of antimicrobial susceptibility testing (AST). It is generally accepted that the biofilm lifestyle has a tremendous impact on antibiotic susceptibility, yet AST is typically still carried out with planktonic cells. On top of that, the microenvironment at the site of infection is an important driver for microbial physiology and hence susceptibility; but this is poorly reflected in current AST methods. The goal of this review is to provide an overview of the state of the art concerning biofilm AST and highlight the knowledge gaps in this area. Subsequently, potential ways to improve biofilm-based AST will be discussed. Finally, bottlenecks currently preventing the use of biofilm AST in clinical practice, as well as the steps needed to get past these bottlenecks, will be discussed.

Novel Antibacterial Agents SAAP-148 and Halicin Combat Gram-Negative Bacteria Colonizing Catheters

The antibiotic management of catheter-related infections (CRIs) often fails owing to the emergence of antimicrobial-resistant strains and/or biofilm/persister apparitions. Thus, we investigated the efficacy of two novel antimicrobial agents, i.e., the synthetic peptide SAAP-148 and the novel antibiotic halicin, against Gram-negative bacteria (GNB) colonizing catheters. The antibacterial, anti-biofilm, and anti-persister activities of both agents were evaluated against Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae strains. The enrolled strains were isolated from catheters and selected based on their resistance to at least three antibiotic classes and biofilm formation potential. Furthermore, the hemolysis and endotoxin neutralization abilities of these agents were explored. The bactericidal activity of both agents was reduced in urine and plasma as compared to buffered saline. In a dose-dependent manner, SAAP-148 and halicin reduced bacterial counts in 24 h preformed biofilms on silicone elastomer discs and eliminated persisters originating from antibiotic-exposed mature 7-day biofilms, with halicin being less effective than SAAP-148. Importantly, SAAP-148 and halicin acted synergistically on E. coli and K. pneumoniae biofilms but not on A. baumannii biofilms. The peptide, but not halicin, decreased the production of IL-12p40 upon exposure to UV-killed bacteria. This preliminary study showed that SAAP-148 and halicin alone/in combination are promising candidates to fight GNB colonizing catheters.

Bioengineering the Antimicrobial Activity of Yeast by Recombinant Thanatin Production

The global spread of antibiotic resistance marks the end of the era of conventional antibiotics. Mankind desires new molecular tools to fight pathogenic bacteria. In this regard, the development of new antimicrobials based on antimicrobial peptides (AMPs) is again of particular interest. AMPs have various mechanisms of action on bacterial cells. Moreover, AMPs have been reported to be efficient in preclinical studies, demonstrating a low level of resistance formation. Thanatin is a small, beta-hairpin antimicrobial peptide with a bacterial-specific mode of action, predetermining its low cytotoxicity toward eukaryotic cells. This makes thanatin an exceptional candidate for new antibiotic development. Here, a microorganism was bioengineered to produce an antimicrobial agent, providing novel opportunities in antibiotic research through the directed creation of biocontrol agents. The constitutive heterologous production of recombinant thanatin (rThan) in the yeast Pichia pastoris endows the latter with antibacterial properties. Optimized expression and purification conditions enable a high production level, yielding up to 20 mg/L of rThan from the culture medium. rThan shows a wide spectrum of activity against pathogenic bacteria, similarly to its chemically synthesized analogue. The designed approach provides new avenues for AMP engineering and creating live biocontrol agents to fight antibiotic resistance.

Biomaterial therapeutic strategies for treatment of bacterial lung infections

Bacterial infections of the lung frequently occur as a secondary infection to many respiratory viral infections and conditions, including influenza, COVID-19, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF). Currently, clinical standard treats bacterial infections of the lung with antibiotic drugs. However, the use of broad-spectrum antibiotics can disrupt host microbiomes, lead to patient discomfort, and current clinical settings face the constantly increasing threat of drug-resistant bacteria. Biofilms further obstruct effective treatment due to their protective matrix layer, which shields bacteria from both the host immune system and antimicrobial drugs and subsequently promotes drug resistance. Alternative antimicrobial agents, including bacteriophages and antimicrobial peptides, have been utilized to treat drug-resistant bacteria. However, these antimicrobial agents have significant limitations pertaining to their ability to arrive at infection sites without compromised function and ability to persist over an extended period to fully treat infections. Enhanced delivery strategies present great promise in addressing these issues by using micro/nanoparticle carriers that shield antimicrobial agents in transit and result in sustained release, enhancing subsequent therapeutic effect and can even be modulated to be multi-functional to further improve recovery following bacterial infection.

Encapsulation in oleyl-modified hyaluronic acid nanogels substantially improves the clinical potential of the antimicrobial peptides SAAP-148 and Ab-Cath

Antimicrobial peptides (AMPs) are promising alternatives to antibiotics for treatment of antimicrobial resistant (AMR) bacterial infections. However, their narrow therapeutic window due to in vivo toxicity and limited stability hampers their clinical use. Here, we evaluated encapsulation of two amphiphilic AMPs, SAAP-148 and snake cathelicidin Ab-Cath, into oleyl-modified hyaluronic acid (OL-HA) nanogels to improve their selectivity index. The AMP-loaded OL-HA nanogels ranged 181-206 nm in size with a PDI of 0.2, highly negative surface charge (-47 to -48 mV) and moderate encapsulation efficiency (53-63%). The AMP-loaded OL-HA nanogels displayed similar activity in vitro as AMP solutions against AMR Staphylococcus aureus and Acinetobacter baumannii, with a dose-dependent effect over time. Importantly, the AMP-loaded OL-HA nanogels showed decreased cytotoxicity towards human erythrocytes and primary skin fibroblast, thereby improving the selectivity index of SAAP-148 and Ab-Cath by 2- and 16.8-fold, respectively. Particularly, the selectivity of Ab-Cath-loaded OL-HA nanogels has great clinical potential, with an index that reached ≥ 300 for S. aureus and ≥ 3000 for A. baumannii. These findings indicate that OL-HA nanogels are a promising drug delivery system to reduce the cytotoxicity of AMPs without substantially affecting their antimicrobial activity, thereby increasing their selectivity index and potential as therapeutics to combat AMR bacterial infections.

Screening and investigation of a short antimicrobial peptide: AVGAV

Bacterial resistance to various drugs is a major problem concerning the field of antibacterial agents. Fortunately, peptides with antibacterial activity can alleviate this problem. In this study, a short peptide (AVGAV) with excellent antibacterial activity was successfully screened from a peptide library by a self-made membrane chromatographic packing. The AVGAV peptide exhibits good biocompatibility and is non-toxic and non-irritating, which ensures that it presents safe antibacterial effects. AVGAV promoted wound healing in a mouse wound bacterial infection model. Most importantly, as a synthetic antimicrobial peptide, AVGAV can alleviate the problem of bacterial resistance, thus improving its application potential. This study provides a solution to the existing and potential problem of bacterial resistance.

Design and synthesis of broad-spectrum antimicrobial amphiphilic peptidomimetics to combat drug-resistance

The gradual depletion of antibiotic discovery pipeline makes the antibiotic resistance a difficult clinical problem and a global health emergency. The membrane-active antimicrobial peptides (AMPs) attracted much attention due to a lower tendency to bacterial resistance than traditional antibiotics. However, some immanent drawbacks of AMPs may hamper their application in combating antibiotic resistance in the long run, such as susceptible to enzymatic degradation and low cell permeability. Herein, we report the design and synthesis of a novel series of amphiphilic peptidomimetics, from which we identified compounds that exhibited potent antimicrobial activity against a panel of clinically relevant Gram-positive and Gram-negative bacteria strains. The most potent compound 20 (SD-110-12) is able to kill intracellular bacterial pathogens and prevent the development of bacterial resistance under the tested conditions by targeting cell membranes. Additionally, compound 20 (SD-110-12) obtains good in vivo efficacy that is comparative to vancomycin by eradicating MRSA and suppressing inflammation in a mice infected skin wound model, demonstrating its promising therapeutic potential.

Activities of a broad-spectrum antimicrobial peptide analogue SAMP-A4-C8 and its combat against pneumonia in Staphylococcus aureus-infected mice

Antimicrobial peptides and their analogues have become substitutes for antibiotics in recent years. The antimicrobial peptide analogue SAMP-A4-C8 (n-octanoic-VRLLRRRI) with high antimicrobial activity was found in our lab. We speculate that it may kill pathogens by some lethal mechanism of action. In the present investigation, the microbicidal activities of SAMP-A4-C8 and its mechanism of action were investigated. The results demonstrated that SAMP-A4-C8 had lethal activities against Staphylococcus aureus and Candida albicans by cell disruption. Based on its microbicidal activities, we believe that it is worth further research for its potential as drug candidate. The results showed that SAMP-A4-C8, with low propensity to induce the resistance of S. aureus and C. albicans, could kill the persister cells of S. aureus and C. albicans, exhibited biofilm forming inhibition activity and preformed biofilm eradication ability against S. aureus and C. albicans, and displayed therapeutic potential on pneumonia in S. aureus-infected mice by reducing lung inflammation. The present study provided a promising drug candidate in the war against multidrug resistance.

A heptadeca amino acid peptide subunit of cathelicidin LL-37 has previously unreported antifungal activity

Yeasts such as Candida albicans, albeit being ubiquitous members of the skin, oral and vaginal microbiome, can cause superficial to life-threatening infections. Human cathelicidin LL-37-based peptides have antibacterial activity and yet, their antifungal activity remains to be thoroughly characterized. The aim of this study was to comprehensively investigate the activity of LL-37-based peptides against C. albicans. LL-37 and its derivatives were tested for their ability to kill C. albicans planktonic cells in the presence of various biological matrices (serum, plasma, saliva and urine), that have been reported to inactivate peptides. The antibiofilm activity, resistance development and biocompatibility were investigated for the lead peptide. GK-17, a 17 amino acid peptide, showed remarkable stability to fungal aspartyl proteases and rapidly killed planktonic C. albicans despite the presence of biological matrices. GK-17 also inhibited adhesion to biotic and abiotic substrates, inhibited biofilm formation and eradicated preformed biofilms in the presence of biological matrices. Compared to nystatin, GK-17 had a lower propensity to allow for resistance development by C. albicans. The peptide showed concentration-dependent biocompatibility to red blood cells, with only 30% hemolysis even at 4× the fungicidal concentration. Taken together, GK-17 is a novel antifungal peptide with promising effects against C. albicans.

Molecular hybridization strategy for tuning bioactive peptide function

The physicochemical and structural properties of antimicrobial peptides (AMPs) determine their mechanism of action and biological function. However, the development of AMPs as therapeutic drugs has been traditionally limited by their toxicity for human cells. Tuning the physicochemical properties of such molecules may abolish toxicity and yield synthetic molecules displaying optimal safety profiles and enhanced antimicrobial activity. Here, natural peptides were modified to improve their activity by the hybridization of sequences from two different active peptide sequences. Hybrid AMPs (hAMPs) were generated by combining the amphipathic faces of the highly toxic peptide VmCT1, derived from scorpion venom, with parts of four other naturally occurring peptides having high antimicrobial activity and low toxicity against human cells. This strategy led to the design of seven synthetic bioactive variants, all of which preserved their structure and presented increased antimicrobial activity (3.1-128 μmol L-1). Five of the peptides (three being hAMPs) presented high antiplasmodial at 0.8 μmol L-1, and virtually no undesired toxic effects against red blood cells. In sum, we demonstrate that peptide hybridization is an effective strategy for redirecting biological activity to generate novel bioactive molecules with desired properties.

Dual-action gallium-flavonoid compounds for combating Pseudomonas aeruginosa infection

The opportunistic pathogen Pseudomonas aeruginosa (P. aeruginosa) causes infections that are difficult to treat, which is due to the bacterial natural resistance to antibiotics. The bacterium is also able to form a biofilm that protects the bacterium from clearance by the human immune system and leads to chronic infection. Herein, we synthesized and characterized a novel gallium compound that interferes with both the iron metabolism and quorum sensing system of P. aeruginosa to achieve a significant bactericidal activity. The compound could substantially reduce the secretion of bacterial virulence factors as well as eliminate biofilm formation. Integrative omics analysis indicates that this compound can significantly disturb the gene transcription and metabolism of P. aeruginosa. The effectiveness of the gallium compound was further validated in mammalian cell and murine skin infection models. Our study offers a new strategy to design new gallium-based antimicrobials to combat P. aeruginosa infection.

Structural-Activity Relationship-Inspired the Discovery of Saturated Fatty Acids as Novel Colistin Enhancers

The emergence and prevalence of mobile colistin resistance gene mcr have dramatically compromised the clinical efficacy of colistin, a cyclopeptide antibiotic considered to be the last option for treating different-to-treat infections. The combination strategy provides a productive and cost-effective strategy to expand the lifespan of existing antibiotics. Structural-activity relationship analysis of polymyxins indicates that the fatty acyl chain plays an indispensable role in their antibacterial activity. Herein, it is revealed that three saturated fatty acids (SFAs), especially sodium caprate (SC), substantially potentiate the antibacterial activity of colistin against mcr-positive bacteria. The combination of SFAs and colistin effectively inhibits biofilm formation and eliminates matured biofilms, and is capable of preventing the emergence and spread of mobile colistin resistance. Mechanistically, the addition of SFAs reduces lipopolysaccharide (LPS) modification by simultaneously promoting LPS biosynthesis and inhibiting the activity of MCR enzyme, enhance bacterial membrane damage, and impair the proton motive force-dependent efflux pump, thereby boosting the action of colistin. In three animal models of infection by mcr-positive pathogens, SC combined with colistin exhibit an excellent therapeutic effect. These findings indicate the therapeutic potential of SFAs as novel antibiotic adjuvants for the treatment of infections caused by multidrug-resistant bacteria in combination with colistin.