Evaluation of short synthetic antimicrobial peptides for treatment of drug-resistant and intracellular Staphylococcus aureus

Antimicrobial peptide-based strategies to overcome antimicrobial resistance

Antibiotic resistance has emerged as a global threat, rendering the existing conventional treatment strategies ineffective. In view of this, antimicrobial peptides (AMPs) have proven to be potent alternative therapeutic interventions with a wide range of applications in clinical health. AMPs are small peptides produced naturally as a part of the innate immune responses against a broad range of bacterial, fungal and viral pathogens. AMPs present a myriad of advantages over traditional antibiotics, including their ability to target multiple sites, reduced susceptibility to resistance development, and high efficacy at low doses. These peptides have demonstrated notable potential in inhibiting microbes resistant to traditional antibiotics, including the notorious ESKAPE pathogens, recognized as the primary culprits behind nosocomial infections. AMPs, with their multifaceted benefits, emerge as promising candidates in the ongoing efforts to combat the escalating challenges posed by antibiotic resistance. This in-depth review provides a detailed discussion on AMPs, encompassing their classification, mechanism of action, and diverse clinical applications. Focus has been laid on combating newly emerging drug-resistant organisms, emphasizing the significance of AMPs in mitigating this pressing challenge. The review also illuminates potential future strategies that may be implemented to improve AMP efficacy, such as structural modifications and using AMPs in combination with antibiotics and matrix-inhibiting compounds.

Investigation on the Synergy between Membrane Permeabilizing Amphiphilic α-Hydrazido Acids and Commonly Used Antibiotics against Drug-Resistant Bacteria

The growth of (multi)drug resistance in bacteria is among the most urgent global health issues. Monocationic amphiphilic α-hydrazido acid derivatives are structurally simple mimics of antimicrobial peptides (AMPs) with fewer drawbacks. Their mechanism of membrane permeabilization at subtoxic concentrations was found to begin with an initial electrostatic attraction of isolated amphiphile molecules to the phospholipid heads, followed by a rapid insertion of the apolar portions. As the accumulation into the bilayer proceeded, the membrane increased its fluidity and permeability without being subjected to major structural damage. After having ascertained that α-hydrazido acid amphiphiles do not interact with bacterial DNA, they were subjected to synergy evaluation for combinations with conventional antibiotics. Synergy was observed for combinations with tetracycline against sensitive S. aureus and E. coli, as well as with ciprofloxacin and colistin against resistant strains. Additivity with a remarkable recovery in activity of conventional antibiotics (from 2-fold to ≥32-fold) together with largely subtoxic concentrations of α-hydrazido acid derivatives was found for combinations with ciprofloxacin toward susceptible S. aureus and methicillin toward MRSa. However, no potentiation of conventional antibiotics was observed for combinations with linezolid and gentamicin against the corresponding resistant S. aureus and E. coli strains.

Non-canonical amino acid bioincorporation into antimicrobial peptides and its challenges

The rise of antimicrobial resistance and multi-drug resistant pathogens has necessitated explorations for novel antibiotic agents as the discovery of conventional antibiotics is becoming economically less viable and technically more challenging for biopharma. Antimicrobial peptides (AMPs) have emerged as a promising alternative because of their particular mode of action, broad spectrum and difficulty that microbes have in becoming resistant to them. The AMPs bacitracin, gramicidin, polymyxins and daptomycin are currently used clinically. However, their susceptibility to proteolytic degradation, toxicity profile, and complexities in large-scale manufacture have hindered their development. To improve their proteolytic stability, methods such as integrating non-canonical amino acids (ncAAs) into their peptide sequence have been adopted, which also improves their potency and spectrum of action. The benefits of ncAA incorporation have been made possible by solid-phase peptide synthesis. However, this method is not always suitable for commercial production of AMPs because of poor yield, scale-up difficulties, and its non-'green' nature. Bioincorporation of ncAA as a method of integration is an emerging field geared towards tackling the challenges of solid-phase synthesis as a green, cheaper, and scalable alternative for commercialisation of AMPs. This review focusses on the bioincorporation of ncAAs; some challenges associated with the methods are outlined, and notes are given on how to overcome these challenges. The review focusses particularly on addressing two key challenges: AMP cytotoxicity towards microbial cell factories and the uptake of ncAAs that are unfavourable to them. Overcoming these challenges will draw us closer to a greater yield and an environmentally friendly and sustainable approach to make AMPs more druggable.

Multi-resistant organisms in burn patients: an end or a new beginning

Infections are a major cause of morbidity and mortality in burn patients, and the rise of multidrug-resistant organisms (MDROs) has made it more challenging to manage and prevent infections. This review examines the available treatment options for MDROs in burn patients and anticipates the future challenges posed by their increasing prevalence. The review covers new antibiotics, such as Eravacycline and Plazomicin, as well as non-antibiotic therapies, such as bacteriophages and nanoparticles. Future research should focus on examining the long-term efficacy, cost-effectiveness, and in vivo efficacy of different treatment modalities. The potential of alternative therapies, such as probiotics and low-frequency magnetic fields, should also be explored. Accurate and rapid diagnostic and monitoring tools for detecting MDROs in burn patients should be developed. The emergence of MDROs in burn care is a challenge and a new beginning in infection innovation and novel treatments.

Methods for screening and evaluation of antimicrobial activity: A review of protocols, advantages, and limitations

Infectious diseases pose a formidable global challenge, compounded by the emergence of antimicrobial resistance. Consequently, researchers are actively exploring novel antimicrobial compounds as potential solutions. This endeavor underscores the pivotal role of methods employed for screening and evaluating antimicrobial activity-a critical step in discovery and characterization of antimicrobial agents. While traditional techniques such as well-diffusion, disk-diffusion, and broth-dilution are commonly utilized in antimicrobial assays, they may encounter limitations concerning reproducibility and speed. Additionally, a diverse array of antimicrobial assays including cross-streaking, poisoned-food, co-culture, time-kill kinetics, resazurin assay, bioautography, etc., are routinely employed in antimicrobial evaluations. Advanced techniques such as flow-cytometry, impedance analysis, and bioluminescent technique may offer rapid and sensitive results, providing deeper insights into the impact of antimicrobials on cellular integrity. However, their higher cost and limited accessibility in certain laboratory settings may present challenges. This article provides a comprehensive overview of assays designed to characterize antimicrobial activity, elucidating their underlying principles, protocols, advantages, and limitations. The primary objective is to enhance understanding of the methodologies designed for evaluating antimicrobial agents in our relentless battle against infectious diseases. By selecting the appropriate antimicrobial testing method, researchers can discern suitable conditions and streamline the identification of effective antimicrobial agents.

Arginine and tryptophan-rich dendritic antimicrobial peptides that disrupt membranes for bacterial infection in vivo

The potent antibacterial activity and low resistance of antimicrobial peptides (AMPs) render them potential candidates for treating multidrug-resistant bacterial infections. Herein, a minimalist design strategy was proposed employing the "golden partner" combination of arginine (R) and tryptophan (W), along with a dendritic structure to design AMPs. By extension, the α/ε-amino group and the carboxyl group of lysine (K) were utilized to link R and W, forming dendritic peptide templates αRn(εRn)KWm-NH2 and αWn(εWn)KRm-NH2, respectively. The corresponding linear peptide templates R2nKWm-NH2 and W2nKRm-NH2 were used as controls. Their physicochemical properties, activity, toxicity, and stability were compared. Among these new peptides, the dendritic peptide R2(R2)KW4 was screened as a prospective candidate owing to its preferable antibacterial properties, biocompatibility, and stability. Additionally, R2(R2)KW4 not only effectively restrained the progression of antibiotic resistance, but also demonstrated synergistic utility when combined with conventional antibiotics due to its unique membrane-disruptive mechanism. Furthermore, R2(R2)KW4 possessed low toxicity (LD50 = 109.31 mg/kg) in vivo, while efficiently clearing E. coli in pulmonary-infected mice. In conclusion, R2(R2)KW4 has the potential to become an antimicrobial regent or adjuvant, and the minimalist design strategy of dendritic peptides provides innovative and encouraging thoughts in designing AMPs.

Emerging strategies and therapeutic innovations for combating drug resistance in Staphylococcus aureus strains: A comprehensive review

In recent years, antibiotic therapy has encountered significant challenges due to the rapid emergence of multidrug resistance among bacteria responsible for life-threatening illnesses, creating uncertainty about the future management of infectious diseases. The escalation of antimicrobial resistance in the post-COVID era compared to the pre-COVID era has raised global concern. The prevalence of nosocomial-related infections, especially outbreaks of drug-resistant strains of Staphylococcus aureus, have been reported worldwide, with India being a notable hotspot for such occurrences. Various virulence factors and mutations characterize nosocomial infections involving S. aureus. The lack of proper alternative treatments leading to increased drug resistance emphasizes the need to investigate and examine recent research to combat future pandemics. In the current genomics era, the application of advanced technologies such as next-generation sequencing (NGS), machine learning (ML), and quantum computing (QC) for genomic analysis and resistance prediction has significantly increased the pace of diagnosing drug-resistant pathogens and insights into genetic intricacies. Despite prompt diagnosis, the elimination of drug-resistant infections remains unattainable in the absence of effective alternative therapies. Researchers are exploring various alternative therapeutic approaches, including phage therapy, antimicrobial peptides, photodynamic therapy, vaccines, host-directed therapies, and more. The proposed review mainly focuses on the resistance journey of S. aureus over the past decade, detailing its resistance mechanisms, prevalence in the subcontinent, innovations in rapid diagnosis of the drug-resistant strains, including the applicants of NGS and ML application along with QC, it helps to design alternative novel therapeutics approaches against S. aureus infection.

Advances in the Synthesis of Biologically Active Quaternary Ammonium Compounds

This review provides a comprehensive overview of recent advancements in the design and synthesis of biologically active quaternary ammonium compounds (QACs). The covered scope extends beyond commonly reviewed antimicrobial derivatives to include synthetic agents with antifungal, anticancer, and antiviral properties. Additionally, this review highlights examples of quaternary ammonium compounds exhibiting activity against protozoa and herbicidal effects, as well as analgesic and anesthetic derivatives. The article also embraces the quaternary-ammonium-containing cholinesterase inhibitors and muscle relaxants. QACs, marked by their inherent permanent charge, also find widespread usage across diverse domains such as fabric softeners, hair conditioners, detergents, and disinfectants. The effectiveness of QACs hinges greatly on finding the right equilibrium between hydrophilicity and lipophilicity. The ideal length of the alkyl chain varies according to the unique structure of each QAC and its biological settings. It is expected that this review will provide comprehensive data for medicinal and industrial chemists to design and develop novel QAC-based products.

A tough, antibacterial and antioxidant hydrogel dressing accelerates wound healing and suppresses hypertrophic scar formation in infected wounds

Wound management is an important issue that places enormous pressure on the physical and mental health of patients, especially in cases of infection, where the increased inflammatory response could lead to severe hypertrophic scars (HSs). In this study, a hydrogel dressing was developed by combining the high strength and toughness, swelling resistance, antibacterial and antioxidant capabilities. The hydrogel matrix was composed of a double network of polyvinyl alcohol (PVA) and agarose with excellent mechanical properties. Hyperbranched polylysine (HBPL), a highly effective antibacterial cationic polymer, and tannic acid (TA), a strong antioxidant molecule, were added to the hydrogel as functional components. Examination of antibacterial and antioxidant properties of the hydrogel confirmed the full play of the efficacy of HBPL and TA. In the in vivo studies of methicillin-resistant Staphylococcus aureus (MRSA) infection, the hydrogel had shown obvious promotion of wound healing, and more profoundly, significant suppression of scar formation. Due to the common raw materials and simple preparation methods, this hydrogel can be mass produced and used for accelerating wound healing while preventing HSs in infected wounds.

Hydrogel Loaded with Peptide-Containing Nanocomplexes: Symphonic Cooperation of Photothermal Antimicrobial Nanoparticles and Prohealing Peptides for the Treatment of Infected Wounds

Current treatment for chronic infectious wounds is limited due to severe drug resistance in certain bacteria. Therefore, the development of new composite hydrogels with nonantibiotic antibacterial and pro-wound repair is important. Here, we present a photothermal antibacterial composite hydrogel fabricated with a coating of Fe2+ cross-linked carboxymethyl chitosan (FeCMCS) following the incorporation of melanin nanoparticles (MNPs) and the CyRL-QN15 peptide. Various physical and photothermal properties of the hydrogel were characterized. Cell proliferation, migration, cycle, and free-radical scavenging activity were assessed, and the antimicrobial properties of the hydrogel were probed by photothermal therapy. The effects of the hydrogel were validated in a model of methicillin-resistant Staphylococcus aureus (MRSA) infection with full-thickness injury. This effect was further confirmed by changes in cytokines associated with inflammation, re-epithelialization, and angiogenesis on the seventh day after wound formation. The MNPs demonstrated robust photothermal conversion capabilities. The composite hydrogel (MNPs/CyRL-QN15/FeCMCS) promoted keratinocyte and fibroblast proliferation and migration while exhibiting high antibacterial efficacy, effectively killing more than 95% of Gram-positive and Gram-negative bacteria. In vivo study using an MRSA-infected full-thickness injury model demonstrated good therapeutic efficacy of the hydrogel in promoting regeneration and remodeling of chronically infected wounds by alleviating inflammatory response and accelerating re-epithelialization and collagen deposition. The MNPs/CyRL-QN15/FeCMCS hydrogel showed excellent antibacterial and prohealing effects on infected wounds, indicating potential as a promising candidate for wound healing promotion.

The Synthetic Peptide LyeTx I mn∆K, Derived from Lycosa erythrognatha Spider Toxin, Is Active against Methicillin-Resistant Staphylococcus aureus (MRSA) In Vitro and In Vivo

The urgent global health challenge posed by methicillin-resistant Staphylococcus aureus (MRSA) infections demands effective solutions. Antimicrobial peptides (AMPs) represent promising tools of research of new antibacterial agents and LyeTx I mn∆K, a short synthetic peptide based on the Lycosa erythrognatha spider venom, is a good representative. This study focused on analyzing the antimicrobial activities of LyeTx I mn∆K, including minimum inhibitory and bactericidal concentrations, synergy and resensitization assays, lysis activity, the effect on biofilm, and the bacterial death curve in MRSA. Additionally, its characterization was conducted through isothermal titration calorimetry, dynamic light scattering, calcein release, and finally, efficacy in a mice wound model. The peptide demonstrates remarkable efficacy against planktonic cells (MIC 8-16 µM) and biofilms (>30% of inhibition) of MRSA, and outperforms vancomycin in terms of rapid bactericidal action and anti-biofilm effects. The mechanism involves significant membrane damage. Interactions with bacterial model membranes, including those with lysylphosphatidylglycerol (LysylPOPG) modifications, highlight the versatility and selectivity of this compound. Also, the peptide has the ability to sensitize resistant bacteria to conventional antibiotics, showing potential for combinatory therapy. Furthermore, using an in vivo model, this study showed that a formulated gel containing the peptide proved superior to vancomycin in treating MRSA-induced wounds in mice. Together, the results highlight LyeTx I mnΔK as a promising prototype for the development of effective therapeutic strategies against superficial MRSA infections.

Peptide recovery from chicken feather keratin and their anti-biofilm properties against methicillin-resistant Staphylococcus aureus (MRSA)

Bacteria have the potential to adhere to abiotic surfaces, which has an undesirable effect in the food industry because they can survive for sustained periods through biofilm formation. In this study, an antibacterial peptide (ABP), with a molecular mass of 3861 Da, was purified from hydrolyzed chicken feathers using a locally isolated keratinolytic bacterium, namely Rhodococcus erythropolis, and its antibacterial and antibiofilm potential were investigated against planktonic and biofilm cells of Methicillin-Resistant Staphylococcus Aureus (MRSA). The results demonstrated that purified ABP showed the growth inhibition of MRSA cells with the minimum inhibitory concentration (MIC) of 45 µg/ml and disrupted MRSA biofilm formation at a concentration of 200 ug/ml, which results were confirmed by scanning electron micrograph (SEM). Moreover, the secondary structures of the peptide were assessed as part of the FTIR analysis to evaluate its mode of action. ExPASy tools were used to predict the ABP sequence, EPCVQUQDSRVVIQPSPVVVVTLPGPILSSFPQNTA, from a chicken feather keratin sequence database following in silico digestion by trypsin. Also, ABP had 54.29% hydrophobic amino acids, potentially contributing to its antimicrobial activity. The findings of toxicity prediction of the peptide by the ToxinPred tool revealed that ABP had non-toxic effects. Thus, these results support the potential of this peptide to be used as an antimicrobial agent for the treatment or prevention of MRSA biofilm formation in feed, food, or pharmaceutical applications.

Evaluation of Novel HLM Peptide Activity and Toxicity against Planktonic and Biofilm Bacteria: Comparison to Standard Antibiotics

BACKGROUND

Antibiotic resistance is one of the main concerns of public health, and the whole world is trying to overcome such a challenge by finding novel therapeutic modalities and approaches. This study has applied the sequence hybridization approach to the original sequence of two cathelicidin natural parent peptides (BMAP-28 and LL-37) to design a novel HLM peptide with broad antimicrobial activity.

METHODS

The physicochemical characteristics of the newly designed peptide were determined. As well, the new peptide's antimicrobial activity (Minimum Inhibitory Concentration (MIC), Minimum Bacterial Eradication Concentration (MBEC), and antibiofilm activity) was tested on two control (Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922) and two resistant (Methicillin-resistant Staphylococcus aureus (MRSA) ATCC BAA41, New Delhi metallo-beta- lactamase-1 Escherichia coli ATCC BAA-2452) bacterial strains. Furthermore, synergistic studies have been applied to HLM-hybridized peptides with five conventional antibiotics by checkerboard assays. Also, the toxicity of HLM-hybridized peptide was studied on Vero cell lines to obtain the IC50 value. Besides the percentage of hemolysis action, the peptide was tested in freshly heparinized blood.

RESULTS

The MIC values for the HLM peptide were obtained as 20, 10, 20, and 20 μM, respectively. Also, the results showed no hemolysis action, with low to slightly moderate toxicity action against mammalian cells, with an IC50 value of 10.06. The Biomatik corporate labs, where HLM was manufactured, determined the stability results of the product by Mass Spectrophotometry (MS) and High-performance Liquid Chromatography (HPLC) methods. The HLM-hybridized peptide exhibited a range of synergistic to additive antimicrobial activities upon combination with five commercially available different antibiotics. It has demonstrated the biofilm-killing effects in the same concentration required to eradicate the control strains.

CONCLUSION

The results indicated that HLM-hybridized peptide displayed a broad-spectrum activity toward different bacterial strains in planktonic and biofilm forms. It showed synergistic or additive antimicrobial activity upon combining with commercially available different antibiotics.

Understanding Staphylococcus aureus internalisation and induction of antimicrobial tolerance

INTRODUCTION

Staphylococcus aureus, a human commensal, is also one of the most common and serious pathogens for humans. In recent years, its capacity to survive and replicate in phagocytic and non-phagocytic cells has been largely demonstrated. In these intracellular niches, bacteria are shielded from the immune response and antibiotics, turning host cells into long-term infectious reservoirs. Moreover, neutrophils carry intracellular bacteria in the bloodstream, leading to systemic spreading of the disease. Despite the serious threat posed by intracellular S. aureus to human health, the molecular mechanisms behind its intracellular survival and subsequent antibiotic treatment failure remain elusive.

AREA COVERED

We give an overview of the killing mechanisms of phagocytes and of the impressive arsenal of virulence factors, toxins and stress responses deployed by S. aureus as a response. We then discuss the different barriers to antibiotic activity in this intracellular niche and finally describe innovative strategies to target intracellular persisting reservoirs.

EXPERT OPINION

Intracellular niches represent a challenge in terms of diagnostic and treatment. Further research using ad-hoc in-vivo models and single cell approaches are needed to better understand the molecular mechanisms underlying intracellular survival and tolerance to antibiotics in order to identify strategies to eliminate these persistent bacteria.

Discovery of bioactive peptides as therapeutic agents for skin wound repair

Short sequences of amino acids called peptides have a wide range of biological functions and the potential to treat a number of diseases. Bioactive peptides can be derived from different sources, including marine organisms, and synthetic design, making them versatile candidates for production of therapeutic agents. Their therapeutic effects span across areas such as antimicrobial activity, cells proliferation and migration, synthesis of collagen, and more. This current review explores the fascinating realm of bioactive peptides as promising therapeutic agents for skin wound healing. This review focuses on the multifaceted biological effects of specific peptides, shedding light on their potential to revolutionize the field of dermatology and regenerative medicine. It delves into how these peptides stimulate collagen synthesis, inhibit inflammation, and accelerate tissue regeneration, ultimately contributing to the effective repair of skin wounds. The findings underscore the significant role several types of bioactive peptides can play in enhancing wound healing processes and offer promising insights for improving the quality of life for individuals with skin injuries and dermatological conditions. The versatility of peptides allows for the development of tailored treatments catering to specific wound types and patient needs. As continuing to delve deeper into the realm of bioactive peptides, there is immense potential for further exploration and innovation. Future endeavors may involve the optimization of peptide formulations, elucidation of underlying molecular and cellular mechanisms.

2,4-Diacetylphloroglucinol (DAPG) derivatives rapidly eradicate methicillin-resistant staphylococcus aureus without resistance development by disrupting membrane

Methicillin-resistant Staphylococcus aureus (MRSA) causes severe public health challenges throughout the world, and the multi-drug resistance (MDR) of MRSA to antibiotics necessitates the development of more effective antibiotics. Natural 2,4-diacetylphloroglucinol (DAPG), produced by Pseudomonas, displays moderate inhibitory activity against MRSA. A series of DAPG derivatives was synthesized and evaluated for their antibacterial activities, and some showed excellent activities (MRSA MIC = 0.5-2 μg/mL). Among these derivatives, 7g demonstrated strong antibacterial activity without resistance development over two months. Mechanistic studies suggest that 7g asserted its activity by targeting bacterial cell membranes. In addition, 7g exhibited significant synergistic antibacterial effects with oxacillin both in vitro and in vivo, with a tendency to eradicate MRSA biofilms. 7g is a promising lead for the treatment of MRSA.

Rapid visualization molecular fluorescence detection of methicillin-resistant Staphylococcus aureus using the multiplex MIRA-qPCR method

Multidrug-resistant (MDR) bacterial infections constitute a major public health problem worldwide. A rapid method for the detection of methicillin-resistant Staphylococcus aureus (MRSA) is critical for the timely prevention of bacterial infections and the accurate clinical use of drugs. The nuc and mecA genes are potentially indicative of MRSA infection and in this study, a multiplex molecular fluorescence multi-enzyme isothermal rapid amplification visual assay was proposed and established. The method is capable of detecting MRSA at 17 min, 40°C amplification, and is well differentiated from common clinical bacteria in specific assays, with 500 colony-forming units (CFU) mL-1 of MRSA detected under optimal conditions. This method has excellent diagnostic capabilities versus classical methods to detect clinical samples and shows potential in the identification of pathogenic microorganisms in a clinical setting.

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.

Hierarchical machine learning model predicts antimicrobial peptide activity against Staphylococcus aureus

Introduction: Staphylococcus aureus is a dangerous pathogen which causes a vast selection of infections. Antimicrobial peptides have been demonstrated as a new hope for developing antibiotic agents against multi-drug-resistant bacteria such as S. aureus. Yet, most studies on developing classification tools for antimicrobial peptide activities do not focus on any specific species, and therefore, their applications are limited. Methods: Here, by using an up-to-date dataset, we have developed a hierarchical machine learning model for classifying peptides with antimicrobial activity against S. aureus. The first-level model classifies peptides into AMPs and non-AMPs. The second-level model classifies AMPs into those active against S. aureus and those not active against this species. Results: Results from both classifiers demonstrate the effectiveness of the hierarchical approach. A comprehensive set of physicochemical and linguistic-based features has been used, and after feature selection steps, only some physicochemical properties were selected. The final model showed the F1-score of 0.80, recall of 0.86, balanced accuracy of 0.80, and specificity of 0.73 on the test set. Discussion: The susceptibility to a single AMP is highly varied among different target species. Therefore, it cannot be concluded that AMP candidates suggested by AMP/non-AMP classifiers are able to show suitable activity against a specific species. Here, we addressed this issue by creating a hierarchical machine learning model which can be used in practical applications for extracting potential antimicrobial peptides against S. aureus from peptide libraries.

Substituted salicylic acid analogs offer improved potency against multidrug-resistant Neisseria gonorrhoeae and good selectivity against commensal vaginal bacteria

Drug-resistant Neisseria gonorrhoeae represents a major threat to public health; without new effective antibiotics, untreatable gonococcal infections loom as a real possibility. In a previous drug-repurposing study, we reported that salicylic acid had good potency against azithromycin-resistant N. gonorrhoeae. We now report that the anti-gonococcal activity in this scaffold is easily lost by inopportune substitution, but that select substituted naphthyl analogs (3b, 3o and 3p) have superior activity to salicylic acid itself. Furthermore, these compounds retained potency against multiple ceftriaxone- and azithromycin-resistant strains, exhibited rapid bactericidal activity against N. gonorrhoeae, and showed high tolerability to mammalian cells (CC50 > 128 µg/mL). Promisingly, these compounds also show very weak growth inhibition of commensal vaginal bacteria.

LL37-Derived Fragments Improve the Antibacterial Potential of Penicillin G and Ampicillin against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infections are a severe threat to public health. Antimicrobial peptides (AMPs) are novel and potential antimicrobials with specific antibacterial mechanisms. Our aim was to study the potential of LL37, FK16, and FK13 to enhance the anti-MRSA activity of antibiotics in vitro, particularly penicillin G and ampicillin. Our results showed that FK16 and FK13 have more synergistic inhibitory effects to MRSA strains when combined with penicillin G and ampicillin. In addition, AMPs exhibited strong membrane permeabilizing properties, and membrane permeabilizing effects can provide a possible explanation for the improved antibacterial effects of antibiotics, since permeabilizing AMPs have the potential to increase the access of antibiotics. To further study the electrostatic interactions among cationic AMPs with negatively charged bacteria, we measured the zeta potentials of three MRSA strains and also neutralized three MRSA strains with the addition of cationic AMPs. Further, we demonstrated the connection between membrane permeabilization and zeta potential neutralization. Finally, we treated MRSA strains with AMPs and characterized the MICs of penicillin G and ampicillin. FK16 was the most promising AMP among the three AMPs, since exposure to FK16 decreased the MICs of both penicillin G and ampicillin for all MRSA strains and also demonstrated more synergistic combinations when combined with antibiotics. AMP exposure and subsequent membrane permeabilization provide a possible pathway to re-sensitize drug-resistant bacteria to traditional antibiotics. Re-sensitization may help preserve the effectiveness of traditional antibiotics, thus providing a potential new strategy for fighting MRSA infections.

The pharmacokinetic-pharmacodynamic modelling framework as a tool to predict drug resistance evolution

Pharmacokinetic-pharmacodynamic (PKPD) models, which describe how drug concentrations change over time and how that affects pathogen growth, have proven highly valuable in designing optimal drug treatments aimed at bacterial eradication. However, the fast rise of antimicrobial resistance calls for increased focus on an additional treatment optimization criterion: avoidance of resistance evolution. We demonstrate here how coupling PKPD and population genetics models can be used to determine treatment regimens that minimize the potential for antimicrobial resistance evolution. Importantly, the resulting modelling framework enables the assessment of resistance evolution in response to dynamic selection pressures, including changes in antimicrobial concentration and the emergence of adaptive phenotypes. Using antibiotics and antimicrobial peptides as an example, we discuss the empirical evidence and intuition behind individual model parameters. We further suggest several extensions of this framework that allow a more comprehensive and realistic prediction of bacterial escape from antimicrobials through various phenotypic and genetic mechanisms.

AMPFinder: A computational model to identify antimicrobial peptides and their functions based on sequence-derived information

Antimicrobial peptides (AMPs) called host defense peptides have existed among all classes of life with 5-100 amino acids generally and can kill mycobacteria, envelop viruses, bacteria, fungi, cancerous cells and so on. Owing to the non-drug resistance of AMP, it has been a wonderful agent to find novel therapies. Therefore, it is urgent to identify AMPs and predict their function in a high-throughput way. In this paper, we propose a cascaded computational model to identify AMPs and their functional type based on sequence-derived and life language embedding, called AMPFinder. Compared with other state-of-the-art methods, AMPFinder obtains higher performance both on AMP identification and AMP function prediction. AMPFinder shows better performance with improvement of F1-score (1.45%-6.13%), MCC (2.92%-12.86%) and AUC (5.13%-8.56%) and AP (9.20%-21.07%) on an independent test dataset. And AMPFinder achieve lower bias of R² on a public dataset by 10-fold cross-validation with an improvement of (18.82%-19.46%). The comparison with other state-of-the-art methods shows that AMP can accurately identify AMP and its function types. The datasets, source code and user-friendly application are available at https://github.com/abcair/AMPFinder.

Antimicrobial peptides´ immune modulation role in intracellular bacterial infection

Intracellular bacteria cause a wide range of diseases, and their intracellular lifestyle makes infections difficult to resolve. Furthermore, standard therapy antibiotics are often unable to eliminate the infection because they have poor cellular uptake and do not reach the concentrations needed to kill bacteria. In this context, antimicrobial peptides (AMPs) are a promising therapeutic approach. AMPs are short cationic peptides. They are essential components of the innate immune response and important candidates for therapy due to their bactericidal properties and ability to modulate host immune responses. AMPs control infections through their diverse immunomodulatory effects stimulating and/or boosting immune responses. This review focuses on AMPs described to treat intracellular bacterial infections and the known immune mechanisms they influence.

Antibiotic-induced accumulation of lipid II synergizes with antimicrobial fatty acids to eradicate bacterial populations

Antibiotic tolerance and antibiotic resistance are the two major obstacles to the efficient and reliable treatment of bacterial infections. Identifying antibiotic adjuvants that sensitize resistant and tolerant bacteria to antibiotic killing may lead to the development of superior treatments with improved outcomes. Vancomycin, a lipid II inhibitor, is a frontline antibiotic for treating methicillin-resistant Staphylococcus aureus and other Gram-positive bacterial infections. However, vancomycin use has led to the increasing prevalence of bacterial strains with reduced susceptibility to vancomycin. Here, we show that unsaturated fatty acids act as potent vancomycin adjuvants to rapidly kill a range of Gram-positive bacteria, including vancomycin-tolerant and resistant populations. The synergistic bactericidal activity relies on the accumulation of membrane-bound cell wall intermediates that generate large fluid patches in the membrane leading to protein delocalization, aberrant septal formation, and loss of membrane integrity. Our findings provide a natural therapeutic option that enhances vancomycin activity against difficult-to-treat pathogens, and the underlying mechanism may be further exploited to develop antimicrobials that target recalcitrant infection.

Antimicrobial peptides for combating drug-resistant bacterial infections

The problem of drug resistance due to long-term use of antibiotics has been a concern for years. As this problem grows worse, infections caused by multiple bacteria are expanding rapidly and are extremely detrimental to human health. Antimicrobial peptides (AMPs) are a good alternative to current antimicrobials with potent antimicrobial activity and unique antimicrobial mechanisms, which have advantages over traditional antibiotics in fighting against drug-resistant bacterial infections. Currently, researchers have conducted clinical investigations on AMPs for drug-resistant bacterial infections while integrating new technologies in the development of AMPs, such as changing amino acid structure of AMPs and using different delivery methods for AMPs. This article introduces the basic properties of AMPs, deliberates the mechanism of drug resistance in bacteria and the therapeutic mechanism of AMPs. The current disadvantages and advances of AMPs in combating drug-resistant bacterial infections are also discussed. This article provides important insights into the research and clinical application of new AMPs for drug-resistant bacterial infections.

A Comprehensive Mechanistic Antibacterial and Antibiofilm Study of Potential Bioactive ((BpA)2bp)Cu/Zn Complexes via Bactericidal Mechanisms against Escherichia coli

Bacterial resistance to antibiotics and host defense systems is primarily due to bacterial biofilm formation in antibiotic therapy. In the present study, two complexes, bis (biphenyl acetate) bipyridine Cu (II) (1) and bis (biphenyl acetate) bipyridine Zn (II) (2), were tested for their ability to prevent biofilm formation. The minimum inhibitory concentration and minimum bactericidal concentration of complexes 1 and 2 were 46.87 ± 1.822 and 93.75 ± 1.345 and 47.87 ± 1.345 and 94.85 ± 1.466 μg/mL, respectively. The significant activity of both complexes was attributed to the damage caused at the membrane level and was confirmed using an imaging technique. The biofilm inhibitory potential levels of complexes 1 and 2 were 95% and 71%, respectively, while the biofilm eradication potential levels were 95% and 35%, respectively, for both complexes. Both the complexes showed good interactions with the E. coli DNA. Thus, complexes 1 and 2 are good antibiofilm agents that exert their bactericidal actions possibly by disrupting the bacterial membrane and interacting with the bacterial DNA, which can act as a powerful agent to restrain the development of bacterial biofilm on therapeutic implants.

Biomaterial mediated immunomodulation: An interplay of material environment interaction for ameliorating wound regeneration

Chronic wounds are the outcome of an imbalanced inflammatory response caused by sustenance of immune microenvironment. In this context, tissue engineered graft played great role in healing wounds but faced difficulty in scar remodelling, immune rejection and poor vascularization. All the limitations faced are somewhere linked with the immune cells involved in healing. In this consideration, immunomodulatory biomaterials bridge a large gap with the delivery of modulating factors for triggering key inflammatory cells responsible towards interplay in the wound micro-environment. Inherent physico-chemical properties of biomaterials substantially determine the nature of cell-materials interaction thereby facilitating differential cytokine gradient involved in activation or suppression of inflammatory signalling pathways, and followed by surface marker expression. This review aims to systematically describe the interplay of immune cells involved in different phases in the wound microenvironment and biomaterials. Additionally, it also focuses on modulating innate immune cell responses in the context of triggering the halted phase of the wound healing, i.e., inflammatory phase. The various strategies are highlighted for modulation of wound microenvironment towards wound regeneration including stem cells, cytokines, growth factors, vitamins, and anti-inflammatory agents to induce interactive ability of biomaterials with immune cells. The last section focuses on prospective approaches and current potential strategies for wound regeneration. This includes the development of different models to bridge the gap between mouse models and human patients. Emerging new tools to study inflammatory response owing to biomaterials and novel strategies for modulation of monocyte and macrophage behaviour in the wound environment are also discussed.

Antimicrobial Spectrum of Activity and Mechanism of Action of Linear Alpha-Helical Peptides Inspired by Shrimp Anti-Lipopolysaccharide Factors

Shrimp antilipopolysaccharide factors (ALFs) form a multifunctional and diverse family of antimicrobial host defense peptides (AMPs) composed of seven members (groups A to G), which differ in terms of their primary structure and biochemical properties. They are amphipathic peptides with two conserved cysteine residues stabilizing a central β-hairpin that is understood to be the core region for their biological activities. In this study, we synthetized three linear (cysteine-free) peptides based on the amino acid sequence of the central β-hairpin of the newly identified shrimp (Litopenaeus vannamei) ALFs from groups E to G. Unlike whole mature ALFs, the ALF-derived peptides exhibited an α-helix secondary structure. In vitro assays revealed that the synthetic peptides display a broad spectrum of activity against both Gram-positive and Gram-negative bacteria and fungi but not against the protozoan parasites Trypanosoma cruzi and Leishmania (L.) infantum. Remarkably, they displayed synergistic effects and showed the ability to permeabilize bacterial membranes, a mechanism of action of classical AMPs. Having shown low cytotoxicity to THP-1 human cells and being active against clinical multiresistant bacterial isolates, these nature-inspired peptides represent an interesting class of bioactive molecules with biotechnological potential for the development of novel therapeutics in medical sciences.

The Emerging Role of Probiotics and their Derivatives against Biofilm-Producing MRSA: A Scoping Review

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main bacterial pathogens causing chronic infections, mainly because of its capacity to produce biofilm. Biofilm production is one of the underlying strategies for antibacterial drug resistance. Accordingly, preventing and attenuating biofilm production has become an emerging approach to controlling persistent infections. Therefore, this scoping review is aimed at surveying the published literature describing the usage of probiotics and their derivatives against biofilm-producing MRSA.

Methods

Updated literature searches were conducted across seven electronic databases including Web of Science, PubMed, Scopus, Cochrane Library, ProQuest, Embase, and Google Scholar to identify all original published articles about probiotics against MRSA. In this regard, studies were summarized and analyzed in the present review.

Results

In the reviewed studies, various microorganisms and compounds were used as probiotics as follows: Lactobacillus species (8 studies), Enterococcus species (4 studies), Bacillus species (2 studies), Streptomyces species (2 studies), Saccharomyces cerevisiae (1 study), Corynebacterium accolens (1 study), and Lactococcus lactis derived Nisin (3 studies). Based on our comprehensive search, 21 studies with eligibility criteria were included in the present review including 12 studies on clinical strains, 6 studies on ATCC, 2 studies simultaneously on clinical and standard strains, and finally 1 study on food sample.

Conclusions

Our study showed that there was an increasing trend in the number of publications reporting probiotics against biofilm-producing MRSA. The results of this scoping review could use to guide the undertaking of the subsequent systematic reviews. In summary, probiotics with antimicrobial and antibiofilm properties can use as an embedded agent in food products or as a biopharmaceutical in the prevention and treatment of MRSA infections.

Injectable hydrogel as a carrier of vancomycin and a cathelicidin-derived peptide for osteomyelitis treatment

A local drug delivery system that attempts to find a suitable balance between antimicrobial and regenerative actions was developed for osteomyelitis treatment (OM). This system combines the angiogenic and immunomodulatory peptide LLKKK18 (LL18) and vancomycin hydrochloride (VH), loaded into an injectable oxidized dextrin (ODEX)-based hydrogel (HG). In vitro cytotoxicity was analyzed in MC3T3-E1 pre-osteoblasts and erythrocytes. The kinetics of LL18 release was studied. Antimicrobial activity was assessed in vitro against a clinical Methicillin-Resistant Staphylococcus aureus (MRSA) strain. A rat model of acute OM was developed by direct inoculation into a tibia defect, concomitantly with the implantation of the drug-loaded HG. The local bioburden was quantified and damage in surrounding tissues was examined histologically. In vitro, ODEX-based HG displayed a safe hemolytic profile. Half of LL18 (53%) is released during the swelling phase at physiological pH, then being gradually released until complete HG degradation. LL18-loaded HG at 300 μM was the most effective peptide formulation in decreasing in vivo infection among concentrations ranging from 86 to 429 μM. The histopathological scores observed in vivo varied with the LL18 concentration in a dose-dependent manner. VH at 28 mM completely eradicated bacteria, although with substantial tissue injury. We have found that sub-millimolar doses of VH combined with LL18 at 300 μM may suffice to eradicate the infection, with reduced tissue damage. We propose an easy-to-handle, shape-fitting HG formulation with the potential to treat MRSA-infected bone with low VH doses associated with LL18.

Bacteriophage-encoded lethal membrane disruptors: Advances in understanding and potential applications

Holins and spanins are bacteriophage-encoded membrane proteins that control bacterial cell lysis in the final stage of the bacteriophage reproductive cycle. Due to their efficient mechanisms for lethal membrane disruption, these proteins are gaining interest in many fields, including the medical, food, biotechnological, and pharmaceutical fields. However, investigating these lethal proteins is challenging due to their toxicity in bacterial expression systems and the resultant low protein yields have hindered their analysis compared to other cell lytic proteins. Therefore, the structural and dynamic properties of holins and spanins in their native environment are not well-understood. In this article we describe recent advances in the classification, purification, and analysis of holin and spanin proteins, which are beginning to overcome the technical barriers to understanding these lethal membrane disrupting proteins, and through this, unlock many potential biotechnological applications.

Antimicrobial peptides for bone tissue engineering: Diversity, effects and applications

Bone tissue engineering has been becoming a promising strategy for surgical bone repair, but the risk of infection during trauma repair remains a problematic health concern worldwide, especially for fracture and infection-caused bone defects. Conventional antibiotics fail to effectively prevent or treat bone infections during bone defect repair because of drug-resistance and recurrence, so novel antibacterial agents with limited resistance are highly needed for bone tissue engineering. Antimicrobial peptides (AMPs) characterized by cationic, hydrophobic and amphipathic properties show great promise to be used as next-generation antibiotics which rarely induce resistance and show potent antibacterial efficacy. In this review, four common structures of AMPs (helix-based, sheet-based, coil-based and composite) and related modifications are presented to identify AMPs and design novel analogs. Then, potential effects of AMPs for bone infection during bone repair are explored, including bactericidal activity, anti-biofilm, immunomodulation and regenerative properties. Moreover, we present distinctive applications of AMPs for topical bone repair, which can be either used by delivery system (surface immobilization, nanoparticles and hydrogels) or used in gene therapy. Finally, future prospects and ongoing challenges are discussed.

Investigation of the Role of Hydrophobic Amino Acids on the Structure-Activity Relationship in the Antimicrobial Venom Peptide Ponericin L1

Venom mixtures from insects, reptiles, and mollusks have long been a source of bioactive peptides which often have alternative uses as therapeutics. While these molecules act in numerous capacities, there have been many venom components that act on the target cells through membrane disruptive mechanisms. These peptides have long been of interest as potential antimicrobial peptide platforms, but the inherent cytotoxicity of venom peptides often results in poor therapeutic potential. Despite this, efforts are ongoing to identify and characterize venom peptide which exhibit high antimicrobial activity with low cytotoxicity and modify these to further enhance the efficacy while reducing toxicity. One example is ponericin L1 from Neoponera goeldii which has been demonstrated to have good antimicrobial activity and low in vitro cytotoxicity. The L1 sequence was modified by uniformly replacing the native hydrophobic residues with either Leu, Ile, Phe, Ala, or Val. Spectroscopic and microbiological approaches were employed to investigate how the amino acid sequence changes impacted membrane interaction, secondary structure, and antimicrobial efficacy. The L1 derivatives showed varying degrees of bilayer interaction, in some cases driven by bilayer composition. Several of the variants exhibited enhanced antimicrobial activity compared to the parent strain, while others lost all activity. Interestingly, the variant containing Val lost all antimicrobial activity and ability to interact with bilayers. Taken together the results indicate that peptide secondary structure, amino acid composition, and hydrophobicity all play a role in peptide activity, although this is a delicate balance that can result in non-specific binding or complete loss of activity if specific amino acids are incorporated.

Eradication of Staphylococcus aureus Biofilm Infection by Persister Drug Combination

Staphylococcus aureus can cause a variety of infections, including persistent biofilm infections, which are difficult to eradicate with current antibiotic treatments. Here, we demonstrate that combining drugs that have robust anti-persister activity, such as clinafloxacin or oritavancin, in combination with drugs that have high activity against growing bacteria, such as vancomycin or meropenem, could completely eradicate S. aureus biofilm bacteria in vitro. In contrast, single or two drugs, including the current treatment doxycycline plus rifampin for persistent S. aureus infection, failed to kill all biofilm bacteria in vitro. In a chronic persistent skin infection mouse model, we showed that the drug combination clinafloxacin + meropenem + daptomycin which killed all biofilm bacteria in vitro completely eradicated S. aureus biofilm infection in mice while the current treatments failed to do so. The complete eradication of biofilm bacteria is attributed to the unique high anti-persister activity of clinafloxacin, which could not be replaced by other fluoroquinolones including moxifloxacin, levofloxacin, or ciprofloxacin. We also compared our persister drug combination with the current approaches for treating persistent infections, including gentamicin + fructose and ADEP4 + rifampin in the S. aureus biofilm infection mouse model, and found neither treatment could eradicate the biofilm infection. Our study demonstrates an important treatment principle, the Yin-Yang model, for persistent infections by targeting both growing and non-growing heterogeneous bacterial populations, utilizing persister drugs for the more effective eradication of persistent and biofilm infections. Our findings have implications for the improved treatment of other persistent and biofilm infections in general.

Green synthesis of metronidazole or clindamycin-loaded hexagonal zinc oxide nanoparticles from Ziziphus extracts and its antibacterial activity

Green chemistry has become a fruitful approach for the synthesis of semiconductors and nanoparticles with various applications. Herein, we synthesized ZnO hexagonal nanoparticles (HNPs) by green precipitation method using fresh local Ziziphus leaf extract (Rhamnaceae) with a heating range of 60–80 in an alkaline medium. It was calcinated on a furnace at 500 °C for 2 h. to get a very fine and homogeneous pale-yellow powder which is then loaded with either metronidazole or clindamycin. The physical characterizations of the particles’ morphology, size, and purity were measured using the Scanning electron microscope, UV-spectroscopy, and the Fourier transform infrared spectroscope. The size of ZnO nanoparticles (44.63 nm) was measured using scanning electron microscopy (SEM), and the mean crystal size of the precursor (17.37 nm) was measured using X-ray diffraction methods (XRD). The antibacterial activity of these particles was measured against Staphylococcus aureus bacterial strains and analyzed using a “well-diffusion technique” which revealed that metronidazole or clindamycin-containing ZnO nanoparticles showed good bactericidal activity.

Keywords

Nickel Nanoparticles: Applications and Antimicrobial Role against Methicillin-Resistant Staphylococcus aureus Infections

Methicillin-resistant Staphylococcus aureus (MRSA) has evolved vast antibiotic resistance. These strains contain numerous virulence factors facilitating the development of severe infections. Considering the costs, side effects, and time duration needed for the synthesis of novel drugs, seeking efficient alternative approaches for the eradication of drug-resistant bacterial agents seems to be an unmet requirement. Nickel nanoparticles (NiNPs) have been applied as prognostic and therapeutic cheap agents to various aspects of biomedical sciences. Their antibacterial effects are exerted via the disruption of the cell membrane, the deformation of proteins, and the inhibition of DNA replication. NiNPs proper traits include high-level chemical stability and binding affinity, ferromagnetic properties, ecofriendliness, and cost-effectiveness. They have outlined pleomorphic and cubic structures. The combined application of NiNPs with CuO, ZnO, and CdO has enhanced their anti-MRSA effects. The NiNPs at an approximate size of around 50 nm have exerted efficient anti-MRSA effects, particularly at higher concentrations. NiNPs have conferred higher antibacterial effects against MRSA than other nosocomial bacterial pathogens. The application of green synthesis and low-cost materials such as albumin and chitosan enhance the efficacy of NPs for therapeutic purposes.

The current research status and strategies employed to modify food-derived bioactive peptides

The ability of bioactive peptides to exert biological functions has mainly contributed to their exploitation. The exploitation and utilization of these peptides have grown tremendously over the past two decades. Food-derived peptides from sources such as plant, animal, and marine proteins and their byproducts constitute a more significant portion of the naturally-occurring peptides that have been documented. Due to their high specificity and biocompatibility, these peptides serve as a suitable alternative to pharmacological drugs for treating non-communicable diseases (such as cardiovascular diseases, obesity, and cancer). They are helpful as food preservatives, ingredients in functional foods, and dietary supplements in the food sector. Despite their unique features, the application of these peptides in the clinical and food sector is to some extent hindered by their inherent drawbacks such as toxicity, bitterness, instability, and susceptibility to enzymatic degradation in the gastrointestinal tract. Several strategies have been employed to eliminate or reduce the disadvantages of peptides, thus enhancing the peptide bioactivity and broadening the opportunities for their applications. This review article focuses on the current research status of various bioactive peptides and the strategies that have been implemented to overcome their disadvantages. It will also highlight future perspectives regarding the possible improvements to be made for the development of bioactive peptides with practical uses and their commercialization.

Tools and techniques for rational designing of antimicrobial peptides for aquaculture

Fisheries and aquaculture industries remain essential sources of food and nutrition for millions of people worldwide. Indiscriminate use of antibiotics has led to the emergence of antimicrobial-resistant bacteria and posed a severe threat to public health. Researchers have opined that antimicrobial peptides (AMPs) can be the best possible alternative to curb the rising tide of antimicrobial resistance in aquaculture. AMPs may also help to achieve the objectives of one health approach. The natural AMPs are associated with several shortcomings, like less in vivo stability, toxicity to host cell, high cost of production and low potency in a biological system. In this review, we have provided a comprehensive outline about the strategies for designing synthetic mimics of natural AMPs with high potency. Moreover, the freely available AMP databases and the information about the molecular docking tools are enlisted. We also provided in silico template for rationally designing the AMPs from fish piscidins or other peptides. The rationally designed piscidin (rP1 and rp2) may be used to tackle microbial infections in aquaculture. Further, the protocol can be used to develop the truncated mimics of natural AMPs having more potency and protease stability.

Fast killing kinetics, significant therapeutic index, and high stability of melittin-derived antimicrobial peptide

The emergence of multidrug-resistant (MDR) bacteria is a major challenge for antimicrobial chemotherapy. Concerning this issue, antimicrobial peptides (AMPs) have been presented as novel promising antibiotics. Our previous de novo designed melittin-derived peptides (MDP1 and MDP2) indicated their potential as peptide drug leads. Accordingly, this study was aimed to evaluate the kinetics of activity, toxicity, and stability of MDP1 and MDP2 as well as determination of their structures. The killing kinetics of MDP1 and MDP2 demonstrate that all bacterial strains were rapidly killed. MDP1 and MDP2 were ca. 100- and 26.6-fold less hemolytic than melittin and found to be respectively 72.9- and 41.6-fold less cytotoxic than melittin on the HEK293 cell line. MDP1 and MDP2 showed 252- and 132-fold improvement in their therapeutic index in comparison to melittin. MDP1 and MDP2 sustained their activities in the presence of human plasma and were found to be ca. four to eightfold more stable than melittin. Spectropolarimetry analysis of MDP1 and MDP2 indicates that the peptides adopt an alpha-helical structure predominantly. According to the fast killing kinetics, significant therapeutic index, and high stability of MDP1, it could be considered as a drug lead in a mouse model of septicemia infections.

Heterogeneous-Backbone Proteomimetic Analogues of Lasiocepsin, a Disulfide-Rich Antimicrobial Peptide with a Compact Tertiary Fold

The emergence of resistance to clinically used antibiotics by bacteria presents a significant problem in public health. Natural antimicrobial peptides (AMPs) are a valuable source of antibiotics that act by a mechanism less prone to the evolutionary development of resistance. In an effort to realize the promise of AMPs while overcoming limitations such as poor biostability, researchers have sought sequence-defined oligomers with artificial amide-based backbones that show membrane-disrupting functions similar to natural agents. Most of this precedent has focused on short peptidomimetic analogues of unstructured chains or secondary folds; however, the natural antimicrobial arsenal includes a number of small- and medium-sized proteins that act via an ordered tertiary structure. Generating proteomimetic analogues of these scaffolds poses a challenge due to the increased complexity of the target for mimicry. Here, we report the development of heterogeneous-backbone variants of lasiocepsin, a 27-residue disulfide-rich AMP found in bee venom that adopts a compact tertiary fold. Iterative cycles of design, synthesis, and biological evaluation yielded analogues of the natural domain with ∼30 to 40% artificial backbone content, comparable antibacterial activity, reduced host cell toxicity, and improved stability to proteolytic degradation. High-resolution structures determined for several variants by NMR provide insights into the interplay among backbone composition, tertiary fold, and biological properties. Collectively, the results reported here broaden the scope of protein functional mimicry by artificial backbone analogues of tertiary folding patterns and suggest protein backbone engineering as a means to tune protein function by exerting site-specific control over protein folded structure.

Recent Strategies to Combat Biofilms Using Antimicrobial Agents and Therapeutic Approaches

Biofilms are intricate bacterial assemblages that attach to diverse surfaces using an extracellular polymeric substance that protects them from the host immune system and conventional antibiotics. Biofilms cause chronic infections that result in millions of deaths around the world every year. Since the antibiotic tolerance mechanism in biofilm is different than that of the planktonic cells due to its multicellular structure, the currently available antibiotics are inadequate to treat biofilm-associated infections which have led to an immense need to find newer treatment options. Over the years, various novel antibiofilm compounds able to fight biofilms have been discovered. In this review, we have focused on the recent and intensively researched therapeutic techniques and antibiofilm agents used for biofilm treatment and grouped them according to their type and mode of action. We also discuss some therapeutic approaches that have the potential for future advancement.

Antibacterial Activity of Small Molecules Which Eradicate Methicillin-Resistant Staphylococcus aureus Persisters

The serious challenge posed by multidrug-resistant bacterial infections with concomitant treatment failure and high mortality rates presents an urgent threat to the global health. We herein report the discovery of a new class of potent antimicrobial compounds that are highly effective against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The compounds were efficiently synthesized in one-pot employing a cascade of Groebke-Blackburn-Bienaymé and aza-Michael addition reactions. Phenotypic screening of the pilot library against various bacterial species including methicillin-sensitive and MRSA strains, has identified potent chemotypes with minimal inhibitory concentrations (MIC) of 3.125-6.25 μg/ml. The most potent compounds were fast-acting at eradicating exponentially growing MRSA, with killing achieved after 30 min of exposure to the compounds. They were also able to kill MRSA persister cells which are tolerant to most available medications. Microscopic analysis using fluorescence microscope and atomic force microscope indicate that these compounds lead to disruption of bacterial cell envelopes. Most notably, bacterial resistance toward these compounds was not observed after 20 serial passages in stark contrast to the significant resistance developed rapidly upon exposure to a clinically relevant antibiotic. Furthermore, the compounds did not induce significant hemolysis to human red blood cells. In vivo safety studies revealed a high safety profile of these motifs. These small molecules hold a promise for further studies and development as new antibacterial agents against MRSA infections.