Anti-microbial, anti-biofilm activities and cell selectivity of the NRC-16 peptide derived from witch flounder, Glyptocephalus cynoglossus

Antibacterial and in vitro anticancer activities of the antimicrobial peptide NRC-07 encapsulated in chitosan nanoparticles

Antimicrobial peptides (AMPs) are promising alternatives to conventional antibiotics and chemotherapy in the treatment of multidrug-resistant pathogens and drug-resistant cancers. Clinical application of AMPs is limited due to low stability and inefficient transport. Encapsulation in nanocarriers may improve their therapeutic potential. Chitosan nanoparticles (CS-NPs) are efficient carriers for proteins and peptides, improving the treatment of microbial infections and targeted drug delivery. We examined toxicity against cancer cell lines and antibacterial activities of the pleurocidin-like AMP NRC-07 upon encapsulation in CS-NPs by ionotropic gelation. The biological activities of various formulations of free and encapsulated NRC-07 and free nanoparticles were evaluated against Pseudomonas aeruginosa and breast cancer cells, using assays for cell viability and lactate dehydrogenase cytolysis with non-cancer cell lines as controls. NRC-07-containing nanoparticles decreased the bacterial and cancer cell viability in a concentration-dependent manner. Activities of encapsulated peptide were >2-fold higher than those of free NRC-07 peptide. Unloaded CS-NPs and free peptide were not cytotoxic against control cells. Encapsulation of NRC-07 into CS-NPs enhanced the antibacterial and selective cytotoxicity of the peptide, possibly enhancing anticancer activities. Encapsulation presents a promising tool for the development of efficient drug delivery systems.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

Pharmacological properties and therapeutic potential of honey bee venom

Honey bee venom (BV) is a valuable product, and has a wide range of biological effects, and its use is rapidly increasing in apitherapy. Therefore, the current study, we reviewed the existing knowledge about BV composition and its numerous pharmacological properties for future research and use. Honey bee venom or apitoxin is produced in the venom gland in the honey bee abdomen. Adult bees use it as a primary colony defense mechanism. It is composed of many biologically active substances including peptides, enzymes, amines, amino acids, phospholipids, minerals, carbohydrates as well as some volatile components. Melittin and phospholipase A₂ are the most important components of BV, having anti-cancer, antimicrobial, anti-inflammatory, anti-arthritis, anti-nociceptive and other curative potentials. Therefore, in medicine, BV has been used for centuries against different diseases like arthritis, rheumatism, back pain, and various inflammatory infections. Nowadays, BV or its components separately, are used for the treatment of various diseases in different countries as a natural medicine with limited side effects. Consequently, scientists as well as several pharmaceutical companies are trying to get a new understanding about BV, its substances and its activity for more effective use of this natural remedy in modern medicine.

Short Antimicrobial Peptides: Therapeutic Potential and Recent Advancements

There has been a lot of interest in antimicrobial peptides (AMPs) as potential next-generation antibiotics. They are components of the innate immune system. AMPs have broad-spectrum action and are less prone to resistance development. They show potential applications in various fields, including medicine, agriculture, and the food industry. However, despite the good activity and safety profiles, AMPs have had difficulty finding success in the clinic due to their various limitations, such as production cost, proteolytic susceptibility, and oral bioavailability. To overcome these flaws, a number of solutions have been devised, one of which is developing short antimicrobial peptides. Short antimicrobial peptides do have an advantage over longer peptides as they are more stable and do not collapse during absorption. They have generated a lot of interest because of their evolutionary success and advantageous properties, such as low molecular weight, selective targets, cell or organelles with minimal toxicity, and enormous therapeutic potential. This article provides an overview of the development of short antimicrobial peptides with an emphasis on those with ≤ 30 amino acid residues as a potential therapeutic agent to fight drug-resistant microorganisms. It also emphasizes their applications in many fields and discusses their current state in clinical trials.

A review on biofilms and the currently available antibiofilm approaches: Matrix-destabilizing hydrolases and anti-bacterial peptides as promising candidates for the food industries

Biofilms are communities of microorganisms that can be harmful and/or beneficial, depending on location and cell content. Since in most cases (such as the formation of biofilms in laboratory/medicinal equipment, water pipes, high humidity-placed structures, and the food packaging machinery) these bacterial and fungal communities are troublesome, researchers in various fields are trying to find a promising strategy to destroy or slow down their formation. In general, anti-biofilm strategies are divided into the plant-based and non-plant categories, with the latter including nanoparticles, bacteriophages, enzymes, surfactants, active peptides and free fatty acids. In most cases, using a single strategy will not be sufficient to eliminate biofilm, and consequently, two or more strategies will inevitably be used to deal with this unwanted phenomenon. According to the analysis of potential biofilm inhibition strategies, the best option for the food industry would be the use of hydrolase enzymes and peptides extracted from natural sources. This article represents a systematic review of the previous efforts made in these directions.

SCMRSA: a New Approach for Identifying and Analyzing Anti-MRSA Peptides Using Estimated Propensity Scores of Dipeptides

Staphylococcus aureus is deemed to be one of the major causes of hospital and community-acquired infections, especially in methicillin-resistant S. aureus (MRSA) strains. Because antimicrobial peptides have captured attention as novel drug candidates due to their rapid and broad-spectrum antimicrobial activity, anti-MRSA peptides have emerged as potential therapeutics for the treatment of bacterial infections. Although experimental approaches can precisely identify anti-MRSA peptides, they are usually cost-ineffective and labor-intensive. Therefore, computational approaches that are able to identify and characterize anti-MRSA peptides by using sequence information are highly desirable. In this study, we present the first computational approach (termed SCMRSA) for identifying and characterizing anti-MRSA peptides by using sequence information without the use of 3D structural information. In SCMRSA, we employed an interpretable scoring card method (SCM) coupled with the estimated propensity scores of 400 dipeptides. Comparative experiments indicated that SCMRSA was more effective and could outperform several machine learning-based classifiers with an accuracy of 0.960 and Matthews correlation coefficient of 0.848 on the independent test data set. In addition, we employed the SCMRSA-derived propensity scores to provide a more in-depth explanation regarding the functional mechanisms of anti-MRSA peptides. Finally, in order to serve community-wide use of the proposed SCMRSA, we established a user-friendly webserver which can be accessed online at http://pmlabstack.pythonanywhere.com/SCMRSA. SCMRSA is anticipated to be an open-source and useful tool for screening and identifying novel anti-MRSA peptides for follow-up experimental studies.

The effect of piscidin antimicrobial peptides on the formation of Gram-negative bacterial biofilms

Fish-derived antimicrobial peptides are an important part of the innate immune system due to their potent antimicrobial properties. Piscidins are a class of antimicrobial peptides first described in hybrid striped bass (Morone chrysops x Morone saxatilis) but have also been identified in many other fish species. Previous work demonstrated the broad antimicrobial activity of piscidins against Gram-negative and Gram-positive bacterial species. This study sought to determine the extent to which class I (striped bass piscidin 1, white bass piscidin 1 and striped bass/white bass piscidin 3) and class II (striped bass piscidin 4 and white bass piscidin 5) piscidins inhibit biofilm formation of different Gram-negative bacteria. In general, the class I and II piscidins demonstrate potent activity against Escherichia coli and Flavobacterium columnare biofilms. The class II piscidins showed more activity against E. coli and F. columnare isolates than did the class I piscidins. The piscidins in general were much less effective against inhibiting Aeromonas hydrophila and A. veronii biofilm growth. Only the class I piscidins showed significant growth inhibition among the Aeromonas spp. examined.

Promising Antimicrobial Properties of Bioactive Compounds from Different Honeybee Products

Bee products have been known for centuries for their versatile healing properties. In recent decades they have become the subject of documented scientific research. This review aims to present and compare the impact of bee products and their components as antimicrobial agents. Honey, propolis, royal jelly and bee venom are bee products that have antibacterial properties. Sensitivity of bacteria to these products varies considerably between products and varieties of the same product depending on their origin. According to the type of bee product, different degrees of activity were observed against Gram-positive and Gram-negative bacteria, yeasts, molds and dermatophytes, as well as biofilm-forming microorganisms. Pseudomonas aeruginosa turned out to be the most resistant to bee products. An analysis of average minimum inhibitory concentration values for bee products showed that bee venom has the strongest bacterial effectiveness, while royal jelly showed the weakest antibacterial activity. The most challenging problems associated with using bee products for medical purposes are dosage and safety. The complexity and variability in composition of these products raise the need for their standardization before safe and predictable clinical uses can be achieved.

Novel Strategies to Combat Bacterial Biofilms

Biofilms are considered as a severe problem in the treatment of bacterial infections; their development causes some noticeable resistance to antibacterial agents. Biofilms are responsible for at least two-thirds of all infections, displaying promoted resistance to classical antibiotic treatments. Therefore, finding new alternative therapeutic approaches is essential for the treatment and inhibition of biofilm-related infections. Therefore, this review aims to describe the potential therapeutic strategies that can inhibit bacterial biofilm development; these include the usage of antiadhesion agents, AMPs, bacteriophages, QSIs, aptamers, NPs and PNAs, which can prevent or eradicate the formation of biofilms. These antibiofilm agents represent a promising therapeutic target in the treatment of biofilm infections and development of a strong capability to interfere with different phases of the biofilm development, including adherence, polysaccharide intercellular adhesion (PIA), quorum sensing molecules and cell-to-cell connection, bacterial aggregation, planktonic bacteria killing and host-immune response modulation. In addition, these components, in combination with antibiotics, can lead to the development of some kind of powerful combined therapy against bacterial biofilm-related infections.

Biofilms as Promoters of Bacterial Antibiotic Resistance and Tolerance

Multidrug resistant bacteria are a global threat for human and animal health. However, they are only part of the problem of antibiotic failure. Another bacterial strategy that contributes to their capacity to withstand antimicrobials is the formation of biofilms. Biofilms are associations of microorganisms embedded a self-produced extracellular matrix. They create particular environments that confer bacterial tolerance and resistance to antibiotics by different mechanisms that depend upon factors such as biofilm composition, architecture, the stage of biofilm development, and growth conditions. The biofilm structure hinders the penetration of antibiotics and may prevent the accumulation of bactericidal concentrations throughout the entire biofilm. In addition, gradients of dispersion of nutrients and oxygen within the biofilm generate different metabolic states of individual cells and favor the development of antibiotic tolerance and bacterial persistence. Furthermore, antimicrobial resistance may develop within biofilms through a variety of mechanisms. The expression of efflux pumps may be induced in various parts of the biofilm and the mutation frequency is induced, while the presence of extracellular DNA and the close contact between cells favor horizontal gene transfer. A deep understanding of the mechanisms by which biofilms cause tolerance/resistance to antibiotics helps to develop novel strategies to fight these infections.

Strategies for antimicrobial peptide coatings on medical devices: a review and regulatory science perspective

Indwelling and implanted medical devices are subject to contamination by microbial pathogens during surgery, insertion or injection, and ongoing use, often resulting in severe nosocomial infections. Antimicrobial peptides (AMPs) offer a promising alternative to conventional antibiotics to reduce the incidence of such infections, as they exhibit broad-spectrum antimicrobial activity against Gram-negative and Gram-positive bacteria, microbial biofilms, fungi, and viruses. In this review-perspective, we first provide an overview of the progress made in this field over the past decade with an emphasis on the local release of AMPs from implant surfaces and immobilization strategies for incorporating these agents into a wide range of medical device materials. We then provide a regulatory science perspective addressing the characterization and testing of AMP coatings based on the type of immobilization strategy used with a focus on the US market regulatory niche. Our goal is to help narrow the gulf between academic studies and preclinical testing, as well as to support a future literature base in order to develop the regulatory science of antimicrobial coatings.

Hindering of Cariogenic Streptococcus mutans Biofilm by Fatty Acid Array Derived from an Endophytic Arthrographis kalrae Strain

Streptococcus mutans has been considered as the major etiological agent of dental caries, mostly due to its arsenal of virulence factors, including strong biofilm formation, exopolysaccharides production, and high acid production. Here, we present the antivirulence activity of fatty acids derived from the endophytic fungus Arthrographis kalrae isolated from Coriandrum sativum against Streptococcus mutans. The chemical composition of the fatty acids was analyzed by gas chromatography-mass spectrometry GC-MS and revealed nine compounds representing 99.6% of fatty acids, where unsaturated and saturated fatty acids formed 93.8% and 5.8 % respectively. Oleic and linoleic acids were the major unsaturated fatty acids. Noteworthy, the fatty acids at the concentration of 31.3 mg L-1 completely inhibited Streptococcus mutans biofilm, and water insoluble extracellular polysaccharide production in both polystyrene plates, and tooth model assay using saliva-coated hydroxyapatite discs. Inhibition of biofilm correlated significantly and positively with the inhibition of water insoluble extracellular polysaccharide (R=1, p <0.0001). Furthermore, Arthrographis kalrae fatty acids at a concentration of 7.8 mg L-1 exhibited acidogenesis-mitigation activity. They did not show bactericidal activity against Streptococcus mutans and cytotoxic activity against human oral fibroblast cells at the concentration used. On the other hand, saliva-coated hydroxyapatite discs treated with sub-minimum biofilm inhibitory concentration of fatty acids showed disturbed biofilm architecture with a few unequally distributed clumped matrices using fluorescence microscopy. Our findings revealed that the intracellular fatty acid arrays derived from endophytic Arthrographis kalrae could contribute to the biofilm-preventing alternatives, specifically Streptococcus mutans biofilms.

Antimicrobial and Antibiofilm Peptides

The increasing onset of multidrug-resistant bacteria has propelled microbiology research towards antimicrobial peptides as new possible antibiotics from natural sources. Antimicrobial peptides are short peptides endowed with a broad range of activity against both Gram-positive and Gram-negative bacteria and are less prone to trigger resistance. Besides their activity against planktonic bacteria, many antimicrobial peptides also show antibiofilm activity. Biofilms are ubiquitous in nature, having the ability to adhere to virtually any surface, either biotic or abiotic, including medical devices, causing chronic infections that are difficult to eradicate. The biofilm matrix protects bacteria from hostile environments, thus contributing to the bacterial resistance to antimicrobial agents. Biofilms are very difficult to treat, with options restricted to the use of large doses of antibiotics or the removal of the infected device. Antimicrobial peptides could represent good candidates to develop new antibiofilm drugs as they can act at different stages of biofilm formation, on disparate molecular targets and with various mechanisms of action. These include inhibition of biofilm formation and adhesion, downregulation of quorum sensing factors, and disruption of the pre-formed biofilm. This review focuses on the proprieties of antimicrobial and antibiofilm peptides, with a particular emphasis on their mechanism of action, reporting several examples of peptides that over time have been shown to have activity against biofilm.

Pan-Drug Resistant Acinetobacter baumannii, but Not Other Strains, Are Resistant to the Bee Venom Peptide Mellitin

Acinetobacter baumannii is a prevalent pathogen in hospital settings with increasing importance in infections associated with biofilm production. Due to a rapid increase in its drug resistance and the failure of commonly available antibiotics to treat A. baumannii infections, this bacterium has become a critical public health issue. For these multi-drug resistant A. baumannii, polymyxin antibiotics are considered the only option for the treatment of severe infections. Concerning, several polymyxin-resistant A. baumannii strains have been isolated over the last few years. This study utilized pan drug-resistant (PDR) strains of A. baumannii isolated in Brazil, along with susceptible (S) and extreme drug-resistant (XDR) strains in order to evaluate the in vitro activity of melittin, an antimicrobial peptide, in comparison to polymyxin and another antibiotic, imipenem. From a broth microdilution method, the determined minimum inhibitory concentration showed that S and XDR strains were susceptible to melittin. In contrast, PDR A. baumannii was resistant to all treatments. Treatment with the peptide was also observed to inhibit biofilm formation of a susceptible strain and appeared to cause permanent membrane damage. A subpopulation of PDR showed membrane damage, however, it was not sufficient to stop bacterial growth, suggesting that alterations involved with antibiotic resistance could also influence melittin resistance. Presumably, mutations in the PDR that have arisen to confer resistance to widely used therapeutics also confer resistance to melittin. Our results demonstrate the potential of melittin to be used in the control of bacterial infections and suggest that antimicrobial peptides can serve as the basis for the development of new treatments.

Calculation of the Global and Local Conceptual DFT Indices for the Prediction of the Chemical Reactivity Properties of Papuamides A-F Marine Drugs

A well-behaved model chemistry previously validated for the study of the chemical reactivity of peptides was considered for the calculation of the molecular properties and structures of the Papuamide family of marine peptides. A methodology based on Conceptual Density Functional Theory (CDFT) was chosen for the determination of the reactivity descriptors. The molecular active sites were associated with the active regions of the molecules related to the nucleophilic and electrophilic Parr functions. Finally, the drug-likenesses and the bioactivity scores for the Papuamide peptides were predicted through a homology methodology relating them with the calculated reactivity descriptors, while other properties such as the pKas were determined following a methodology developed by our group.

Challenges of intervention, treatment, and antibiotic resistance of biofilm-forming microorganisms

Background

Biofilms are multicellular communities of microorganisms held together by a self-produced extracellular matrix. The ability of microbes to form biofilm is a universal, ubiquitous, and dynamic process. This dynamic process of biofilms establishes an important strategy to withstand and survive harsh environmental conditions and antimicrobial agents.

Objective

This review paper aims to give an overview of antibiotic resistance, intervention, and treatment of infections caused by biofilm-forming organisms. Moreover, it can also help to motivate scholars to search for new anti-biofilm strategies and most appropriate methods to tackle the effect of biofilm infections on healthcare services.

Methods

This paper was written by reviewing recent research and review articles which are reporting about the antibiotic resistance, prevention, and treatment of biofilm-producing organisms.

Conclusion

Bioprospecting for quorum quenching compounds can be an appropriate solution for controlling biofilm infections.

How Melittin Inserts into Cell Membrane: Conformational Changes, Inter-Peptide Cooperation, and Disturbance on the Membrane

Antimicrobial peptides (AMPs), as a key component of the immune defense systems of organisms, are a promising solution to the serious threat of drug-resistant bacteria to public health. As one of the most representative and extensively studied AMPs, melittin has exceptional broad-spectrum activities against microorganisms, including both Gram-positive and Gram-negative bacteria. Unfortunately, the action mechanism of melittin with bacterial membranes, especially the underlying physics of peptide-induced membrane poration behaviors, is still poorly understood, which hampers efforts to develop melittin-based drugs or agents for clinical applications. In this mini-review, we focus on recent advances with respect to the membrane insertion behavior of melittin mostly from a computational aspect. Membrane insertion is a prerequisite and key step for forming transmembrane pores and bacterial killing by melittin, whose occurrence is based on overcoming a high free-energy barrier during the transition of melittin molecules from a membrane surface-binding state to a transmembrane-inserting state. Here, intriguing simulation results on such transition are highlighted from both kinetic and thermodynamic aspects. The conformational changes and inter-peptide cooperation of melittin molecules, as well as melittin-induced disturbances to membrane structure, such as deformation and lipid extraction, are regarded as key factors influencing the insertion of peptides into membranes. The associated intermediate states in peptide conformations, lipid arrangements, membrane structure, and mechanical properties during this process are specifically discussed. Finally, potential strategies for enhancing the poration ability and improving the antimicrobial performance of AMPs are included as well.

A Synthetic Derivative of Antimicrobial Peptide Holothuroidin 2 from Mediterranean Sea Cucumber (Holothuria tubulosa) in the Control of Listeria monocytogenes

Due to the limited number of available antibiotics, antimicrobial peptides (AMPs) are considered antimicrobial candidates to fight difficult-to-treat infections such as those associated with biofilms. Marine environments are precious sources of AMPs, as shown by the recent discovery of antibiofilm properties of Holothuroidin 2 (H2), an AMP produced by the Mediterranean sea cucumber Holothuria tubulosa. In this study, we considered the properties of a new H2 derivative, named H2d, and we tested it against seven strains of the dangerous foodborne pathogen Listeria monocytogenes. This peptide was more active than H2 in inhibiting the growth of planktonic L. monocytogenes and was able to interfere with biofilm formation at sub-minimum inhibitory concentrations (MICs). Atomic-level molecular dynamics (MD) simulations revealed insights related to the enhanced inhibitory activity of H2d, showing that the peptide is characterized by a more defined tertiary structure with respect to its ancestor. This allows the peptide to better exhibit an amphipathic character, which is an essential requirement for the interaction with cell membranes, similarly to other AMPs. Altogether, these results support the potential use of our synthetic peptide, H2d, as a template for the development of novel AMP-based drugs able to fight foodborne that are resistant to conventional antibiotics.

Going beyond the Control of Quorum-Sensing to Combat Biofilm Infections

Most bacteria attach to surfaces where they form a biofilm, cells embedded in a complex matrix of polymers. Cells in biofilms are much better protected against noxious agents than free-living cells. As a consequence it is very difficult to control pathogens with antibiotics in biofilm infections and novel targets are urgently needed. One approach aims at the communication between cells to form and to maintain a biofilm, a process called quorum-sensing. Water soluble small-sized molecules mediate this process and a number of antagonists of these compounds have been found. In this review natural compounds and synthetic drugs which do not interfere with the classical quorum-sensing compounds are discussed. For some of these compounds the targets are still not known, but others interfere with the formation of exopolysaccharides, virulence factors, or cell wall synthesis or they start an internal program of biofilm dispersal. Some of their targets are more conserved among pathogens than the receptors for quorum sensing autoinducers mediating quorum-sensing, enabling a broader application of the drug. The broad spectrum of mechanisms, the diversity of bioactive compounds, their activity against several targets, and the conservation of some targets among bacterial pathogens are promising aspects for several clinical applications of this type of biofilm-controlling compound in the future.

Synthetic antibiofilm peptides

Bacteria predominantly exist as multicellular aggregates known as biofilms that are associated with at least two thirds of all infections and exhibit increased adaptive resistance to conventional antibiotic therapies. Therefore, biofilms are major contributors to the global health problem of antibiotic resistance, and novel approaches to counter them are urgently needed. Small molecules of the innate immune system called host defense peptides (HDPs) have emerged as promising templates for the design of potent, broad-spectrum antibiofilm agents. Here, we review recent developments in the new field of synthetic antibiofilm peptides, including mechanistic insights, synergistic interactions with available antibiotics, and their potential as novel antimicrobials against persistent infections caused by biofilms. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Inhibitory Effects of Antimicrobial Peptides on Lipopolysaccharide-Induced Inflammation

Antimicrobial peptides (AMPs) are usually small molecule peptides, which display broad-spectrum antimicrobial activity, high efficiency, and stability. For the multiple-antibiotic-resistant strains, AMPs play a significant role in the development of novel antibiotics because of their broad-spectrum antimicrobial activities and specific antimicrobial mechanism. Besides broad-spectrum antibacterial activity, AMPs also have anti-inflammatory activity. The neutralization of lipopolysaccharides (LPS) plays a key role in anti-inflammatory action of AMPs. On the one hand, AMPs can readily penetrate the cell wall barrier by neutralizing LPS to remove Gram-negative bacteria that can lead to infection. On the contrary, AMPs can also inhibit the production of biological inflammatory cytokines to reduce the inflammatory response through neutralizing circulating LPS. In addition, AMPs also modulate the host immune system by chemotaxis of leukocytes, to promote immune cell proliferation, epithelialization, and angiogenesis and thus play a protective role. This review summarizes some recent researches about anti-inflammatory AMPs, with a focus on the interaction of AMPs and LPS on the past decade.

Short antimicrobial peptides as cosmetic ingredients to deter dermatological pathogens

Antimicrobial peptides (AMPs) are components of the innate immune system in many species of animals. Their diverse spectrum of activity against microbial pathogens, both as innate defense molecules and immunomodulators, makes them attractive candidates for the development of a new generation of antibiotics. Although the potential immunogenicity of AMPs means they are not suitable for injection and their susceptibility to digestive peptidases is likely to reduce their oral efficacy, they are ideal for topical formulations such as lotions, creams, shampoos, and wound dressings and could therefore be valuable products for the cosmetic industry. In this context, short AMPs (<20 amino acids) lacking disulfide bonds combine optimal antimicrobial activity with inexpensive chemical synthesis and are therefore more compatible with large-scale production and the modifications required to ensure stability, low toxicity, and microbial specificity. Proof-of-concept for the application of AMPs as novel anti-infectives has already been provided in clinical trials. This perspective considers the anti-infective properties of short AMPs lacking disulfide bonds, which are active against dermatologically important microflora. We consider the challenges that need to be addressed to facilitate the prophylactic application of AMPs in personal care products.

Interaction of cyclic and linear Labaditin peptides with anionic and zwitterionic micelles

Conformational changes of the cyclic (Lo) peptide Labaditin (VWTVWGTIAG) and its linear analogue (L1) promoted by presence of anionic sodium dodecyl sulfate (SDS) and zwitterionic L-α-Lysophosphatidylcholine (LPC) micelles were investigated. Results from λ(max) blue-shift of tryptophan fluorescence emission combined with Stern-Volmer constants values and molecular dynamics (MD) simulations indicated that L1 interacts with SDS micelles to a higher extent than does Lo. Further, the MD simulation demonstrated that both Lo and L1 interact similarly with LPC micelles, being preferentially located at the micelle/water interface. The peptide-micelle interaction elicits conformational changes in the peptides. Lo undergoes limited modifications and presents unordered structure in both LPC and SDS micelles. On the other hand, L1 displays a random-coil structure in aqueous medium, pH 7.0, and it acquires a β-structure upon interaction with SDS and LPC, albeit with structural differences in each medium.

The role of biophysical parameters in the antilipopolysaccharide activities of antimicrobial peptides from marine fish

Numerous antimicrobial peptides (AMPs) from marine fish have been identified, isolated and characterized. These peptides act as host defense molecules that exert antimicrobial effects by targeting the lipopolysaccharide (LPS) of Gram-negative bacteria. The LPS-AMP interactions are driven by the biophysical properties of AMPs. In this review, therefore, we will focus on the physiochemical properties of AMPs; that is, the contributions made by their sequences, net charge, hydrophobicity and amphipathicity to their mechanism of action. Moreover, the interactions between LPS and fish AMPs and the structure of fish AMPs with LPS bound will also be discussed. A better understanding of the biophysical properties will be useful in the design of AMPs effective against septic shock and multidrug-resistant bacterial strains, including those that commonly produce wound infections.

Treatment of microbial biofilms in the post-antibiotic era: prophylactic and therapeutic use of antimicrobial peptides and their design by bioinformatics tools

The treatment for biofilm infections is particularly challenging because bacteria in these conditions become refractory to antibiotic drugs. The reduced effectiveness of current therapies spurs research for the identification of novel molecules endowed with antimicrobial activities and new mechanisms of antibiofilm action. Antimicrobial peptides (AMPs) have been receiving increasing attention as potential therapeutic agents, because they represent a novel class of antibiotics with a wide spectrum of activity and a low rate in inducing bacterial resistance. Over the past decades, a large number of naturally occurring AMPs have been identified or predicted from various organisms as effector molecules of the innate immune system playing a crucial role in the first line of defense. Recent studies have shown the ability of some AMPs to act against microbial biofilms, in particular during early phases of biofilm development. Here, we provide a review of the antimicrobial peptides tested on biofilms, highlighting their advantages and disadvantages for prophylactic and therapeutic applications. In addition, we describe the strategies and methods for de novo design of potentially active AMPs and discuss how informatics and computational tools may be exploited to improve antibiofilm effectiveness.

Synergistic effects and antibiofilm properties of chimeric peptides against multidrug-resistant Acinetobacter baumannii strains

The increasing prevalence of drug-resistant pathogens highlights the need to identify novel antibiotics. Here we investigated the efficacies of four new antimicrobial peptides (AMPs) for potential drug development. The antibacterial activities, synergistic effects, and antibiofilm properties of the four chimeric AMPs were tested against Acinetobacter baumannii, an emerging Gram-negative, nosocomial, drug-resistant pathogen. Nineteen A. baumannii strains resistant to ampicillin, cefotaxime, ciprofloxacin, tobramycin, and erythromycin were isolated at a hospital from patients with cholelithiasis. All four peptides exhibited significant antibacterial effects (MIC=3.12 to 12.5 μM) against all 19 strains, whereas five commercial antibiotics showed little or no activity against the same pathogens. An exception was polymyxin, which was effective against all of the strains tested. Each of the peptides showed synergy against one or more strains when administered in combination with cefotaxime, ciprofloxacin, or erythromycin. The peptides also exhibited an ability to prevent biofilm formation, which was not seen with cefotaxime, ciprofloxacin, or erythromycin, though polymyxin also inhibited biofilm formation. Indeed, when administered in combination with ciprofloxacin, the AMP HPMA exerted a potent synergistic effect against A. baumannii biofilm formation. Collectively, our findings indicate that the AMPs tested have no cytotoxicity but possess potent antibacterial and antibiofilm activities and may act synergistically with commercial antibiotics.

Antimicrobial peptides

The rapid increase in drug-resistant infections has presented a serious challenge to antimicrobial therapies. The failure of the most potent antibiotics to kill “superbugs” emphasizes the urgent need to develop other control agents. Here we review the history and new development of antimicrobial peptides (AMPs), a growing class of natural and synthetic peptides with a wide spectrum of targets including viruses, bacteria, fungi, and parasites. We summarize the major types of AMPs, their modes of action, and the common mechanisms of AMP resistance. In addition, we discuss the principles for designing effective AMPs and the potential of using AMPs to control biofilms (multicellular structures of bacteria embedded in extracellular matrixes) and persister cells (dormant phenotypic variants of bacterial cells that are highly tolerant to antibiotics).