Hydrophobic Interactions in Complexes of Antimicrobial Peptides with Bacterial Polysaccharides

A Novel Method for the Preparation of Casein-Fucoidan Composite Nanostructures

The aim of the study was to develop casein-fucoidan composite nanostructures through the method of polyelectrolyte complexation and subsequent spray drying. To determine the optimal parameters for the preparation of the composite structures and to investigate the influence of the production and technological parameters on the main structural and morphological characteristics of the obtained structures, 3(k-p) fractional factorial design was applied. The independent variables (casein to fucoidan ratio, glutaraldehyde concentration, and spray intensity) were varied at three levels (low, medium, and high) and their effect on the yield, the average particle size, and the zeta potential were evaluated statistically. Based on the obtained results, models C1F1G1Sp.30, C1F1G2Sp.40, and C1F1G3Sp.50, which have an average particle size ranging from (0.265 ± 0.03) µm to (0.357 ± 0.02) µm, a production yield in the range (48.9 ± 2.9) % to (66.4 ± 2.2) %, and a zeta potential varying from (-20.12 ± 0.9) mV to (-25.71 ± 1.0) mV, were selected as optimal for further use as drug delivery systems.

Potential of Pm11 antimicrobial peptide against bovine mastitis pathogens

OBJECTIVE

To investigate an alternative treatment for bovine mastitis by using Pm11 antimicrobial peptide.

SAMPLE

5 bovine mastitis pathogens that were previously isolated from cows affected by either clinical or subclinical mastitis.

PROCEDURES

The current study introduces Pm11 antimicrobial peptide as an alternative treatment for bovine mastitis. The antibacterial activity of Pm11 was tested against Escherichia coli strain SCM1249, Klebsiella spp strain SCM1282, Staphylococcus aureus strain CM967, Streptococcus agalactiae strain SCM1084, and Streptococcus uberis strain SCM1310 using minimum bactericidal concentrations (MBCs) and time-kill kinetics. The pathogens' morphological changes were demonstrated using a scanning electron microscope (SEM). The cytotoxicity of Pm11 was assessed using the minimum hemolytic concentration assay.

RESULTS

MBCs ranged from 2.5 to 10 μM and IC50 ranged from 0.32 to 2.07 μM. Time-kill kinetics at MBC demonstrated that Pm11 reduced viable cell counts of S agalactiae strain SCM1084 and S uberis strain SCM1310 from 105 to 0 CFU/mL within 1 h. E coli strain SCM1249 and S aureus strain CM967 were reduced from 105 to 0 CFU/mL within 4 h. The average Pm11-induced hemolytic activity was < 10% for all Pm11 concentrations tested except at the maximum concentration tested (160 μM: 10.19 ± 2.29%). Based on SEM, Pm11 induced morphological and cellular changes in S aureus and E coli.

CLINICAL RELEVANCE

Pm11 antimicrobial peptide demonstrated in vitro antibacterial activity against the common bovine mastitis pathogens E coli, S aureus, S agalactiae, and S uberis, except Klebsiella spp, and should be further investigated in vivo.

Unaided efficient transglutaminase cross-linking of whey proteins strongly impacts the formation and structure of protein alginate particles

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Microbial transglutaminase (MTG) cross-linked >70% β-lactoglobulin (β-Lg) at pH 8.5.

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Initial MTG catalyzed isopeptide bond formation caused partial unfolding of β-Lg.

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>75% of whey protein cross-linked, forming hetero-polymers containing β-Lg.

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50% less alginate is needed to form particles with cross-linked than with native β-Lg.

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Cross-linked β-Lg and alginate formed suspendable hydrophobically driven particles.

There is a dogma within whey protein modification, which dictates the necessity of pretreatment to enzymatic cross-linking of β-lactoglobulin (β-Lg). Here microbial transglutaminase (MTG) cross-linked whey proteins and β-Lg effectively in 50 mM NaHCO₃, pH 8.5, without pretreatment. Cross-linked β-Lg spanned 18 to >240 kDa, where 6 of 9 glutamines reacted with 8 of 15 lysines. The initial isopeptide bond formation caused loss of β-Lg native structure with t_1/2 = 3 h, while the polymerization occurred with t_1/2 = 10 h. Further, cross-linking effects on protein carbohydrate interaction have been overlooked, leaving a gap in understanding of these complex food matrices. Complexation with alginate showed that β-Lg cross-linking decreased onset of particle formation, hydrodynamic diameter, stoichiometry (β-Lg/alginate) and dissociation constant. The complexation was favored at higher temperatures (40 °C), suggesting that hydrophobic interactions were important. Thus, β-Lg was cross-linked without pretreatment and the resulting polymers gave rise to altered complexation with alginate.

Protein Stabilization by Alginate Binding and Suppression of Thermal Aggregation

Polymers designed to stabilize proteins exploit direct interactions or crowding, but mechanisms underlying increased stability or reduced aggregation are rarely established. Alginate is widely used to encapsulate proteins for drug delivery and tissue regeneration despite limited knowledge of its impact on protein stability. Here, we present evidence that alginate can both increase protein folding stability and suppress the aggregation of unfolded protein through direct interactions without crowding. We used a fluorescence-based conformational reporter of two proteins, the metabolic protein phosphoglycerate kinase (PGK) and the hPin1 WW domain to monitor protein stability and aggregation as a function of temperature and the weight percent of alginate in solution. Alginate stabilizes PGK by up to 14.5 °C, but stabilization is highly protein-dependent, and the much smaller WW domain is stabilized by only 3.5 °C against thermal denaturation. Stabilization is greatest at low alginate weight percent and decreases at higher alginate concentrations. This trend cannot be explained by crowding, and ionic screening suggests that alginate stabilizes proteins through direct interactions with a significant electrostatic component. Alginate also strongly suppresses aggregation at high temperature by irreversibly associating with unfolded proteins and preventing refolding. Both the beneficial and negative impacts of alginate on protein stability and aggregation have important implications for practical applications.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

The multifaceted nature of antimicrobial peptides: current synthetic chemistry approaches and future directions

Bacterial infections caused by 'superbugs' are increasing globally, and conventional antibiotics are becoming less effective against these bacteria, such that we risk entering a post-antibiotic era. In recent years, antimicrobial peptides (AMPs) have gained significant attention for their clinical potential as a new class of antibiotics to combat antimicrobial resistance. In this review, we discuss several facets of AMPs including their diversity, physicochemical properties, mechanisms of action, and effects of environmental factors on these features. This review outlines various chemical synthetic strategies that have been applied to develop novel AMPs, including chemical modifications of existing peptides, semi-synthesis, and computer-aided design. We will also highlight novel AMP structures, including hybrids, antimicrobial dendrimers and polypeptides, peptidomimetics, and AMP-drug conjugates and consider recent developments in their chemical synthesis.

Defining principles that influence antimicrobial peptide activity against capsulated Klebsiella pneumoniae

The extracellular polysaccharide capsule of Klebsiella pneumoniae resists penetration by antimicrobials and protects the bacteria from the innate immune system. Host antimicrobial peptides are inactivated by the capsule as it impedes their penetration to the bacterial membrane. While the capsule sequesters most peptides, a few antimicrobial peptides have been identified that retain activity against encapsulated K. pneumoniae, suggesting that this bacterial defense can be overcome. However, it is unclear what factors allow peptides to avoid capsule inhibition. To address this, we created a peptide analog with strong antimicrobial activity toward several K. pneumoniae strains from a previously inactive peptide. We characterized the effects of these two peptides on K. pneumoniae, along with their physical interactions with K. pneumoniae capsule. Both peptides disrupted bacterial cell membranes, but only the active peptide displayed this activity against capsulated K. pneumoniae Unexpectedly, the active peptide showed no decrease in capsule binding, but did lose secondary structure in a capsule-dependent fashion compared with the inactive parent peptide. We found that these characteristics are associated with capsule-peptide aggregation, leading to disruption of the K. pneumoniae capsule. Our findings reveal a potential mechanism for disrupting the protective barrier that K. pneumoniae uses to avoid the immune system and last-resort antibiotics.

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.

Assembly of Protein-Polysaccharide Complexes for Delivery of Bioactive Ingredients: A Perspective Paper

Protein-polysaccharide complexes can be created in various ways (physical mixing, enzymatic cross-linking, chemical cross-linking, and Maillard reaction), and diverse protein-polysaccharide complexes are generally grouped into non-covalent and covalent complexes. Delivery systems constructed through assembly of protein-polysaccharide complexes (DSAPC) consist of emulsion-based delivery systems, capsule-based delivery systems, molecular complexes, nanogels, core-shell particles, composite nanoparticles, and micelles. DSAPC are effective delivery vehicles in enhancing the overall efficacy of bioactive ingredients, and DSAPC may possess multiple advantages over other delivery vehicles in bioactive ingredient delivery. However, designing and applying DSAPC are still faced with some challenges, such as low loading of bioactive ingredients. Efforts are required to reconsider and improve efficiency of DSAPC in many aspects, such as controlled release and targeted delivery. On the basis of more comprehensive and deeper understandings, DSAPC can be designed more rationally for delivery of bioactive ingredients.

Action of Antimicrobial Peptides against Bacterial Biofilms

Microbes are known to colonize surfaces and form biofilms. These biofilms are communities of microbes encased in a self-produced matrix that often contains polysaccharides, DNA and proteins. Antimicrobial peptides (AMPs) have been used to control the formation and to eradicate mature biofilms. Naturally occurring or synthetic antimicrobial peptides have been shown to prevent microbial colonization of surfaces, to kill bacteria in biofilms and to disrupt the biofilm structure. This review systemically analyzed published data since 1970 to summarize the possible anti-biofilm mechanisms of AMPs. One hundred and sixty-two published reports were initially selected for this review following searches using the criteria ‘antimicrobial peptide’ OR ‘peptide’ AND ‘mechanism of action’ AND ‘biofilm’ OR ‘antibiofilm’ in the databases PubMed; Scopus; Web of Science; MEDLINE; and Cochrane Library. Studies that investigated anti-biofilm activities without describing the possible mechanisms were removed from the analysis. A total of 17 original reports were included which have articulated the mechanism of antimicrobial action of AMPs against biofilms. The major anti-biofilm mechanisms of antimicrobial peptides are: (1) disruption or degradation of the membrane potential of biofilm embedded cells; (2) interruption of bacterial cell signaling systems; (3) degradation of the polysaccharide and biofilm matrix; (4) inhibition of the alarmone system to avoid the bacterial stringent response; (5) downregulation of genes responsible for biofilm formation and transportation of binding proteins.

Identification of Novel Cryptic Multifunctional Antimicrobial Peptides from the Human Stomach Enabled by a Computational-Experimental Platform

Novel approaches are needed to combat antibiotic resistance. Here, we describe a computational-experimental framework for the discovery of novel cryptic antimicrobial peptides (AMPs). The computational platform, based on previously validated antimicrobial scoring functions, indicated the activation peptide of pepsin A, the main human stomach protease, and its N- and C-terminal halves as antimicrobial peptides. The three peptides from pepsinogen A3 isoform were prepared in a recombinant form using a fusion carrier specifically developed to express toxic peptides in Escherichia coli. Recombinant pepsinogen A3-derived peptides proved to be wide-spectrum antimicrobial agents with MIC values in the range 1.56-50 μM (1.56-12.5 μM for the whole activation peptide). Moreover, the activation peptide was bactericidal at pH 3.5 for relevant foodborne pathogens, suggesting that this new class of previously unexplored AMPs may contribute to microbial surveillance within the human stomach. The peptides showed no toxicity toward human cells and exhibited anti-infective activity in vivo, reducing by up to 4 orders of magnitude the bacterial load in a mouse skin infection model. These peptides thus represent a promising new class of antibiotics. We envision that computationally guided data mining approaches such as the one described here will lead to the discovery of antibiotics from previously unexplored sources.

The particle in the spider's web: transport through biological hydrogels

Biological hydrogels such as mucus, extracellular matrix, biofilms, and the nuclear pore have diverse functions and compositions, but all act as selectively permeable barriers to the diffusion of particles. Each barrier has a crosslinked polymeric mesh that blocks penetration of large particles such as pathogens, nanotherapeutics, or macromolecules. These polymeric meshes also employ interactive filtering, in which affinity between solutes and the gel matrix controls permeability. Interactive filtering affects the transport of particles of all sizes including peptides, antibiotics, and nanoparticles and in many cases this filtering can be described in terms of the effects of charge and hydrophobicity. The concepts described in this review can guide strategies to exploit or overcome gel barriers, particularly for applications in diagnostics, pharmacology, biomaterials, and drug delivery.

Alginate gel particles-A review of production techniques and physical properties

The application of hydrocolloid gel particles is potentially useful in food, chemical, and pharmaceutical industries. Alginate gel particles are one of the more commonly used hydrocolloid gel particles due to them being biocompatible, nontoxic, biodegradable, cheap, and simple to produce. They are particularly valued for their application in encapsulation. Encapsulation in alginate gel particles confers protective benefits to cells, DNA, nutrients, and microbes. Slow release of flavors, minerals, and drugs can also be achieved by encapsulation in gel particles. The particle size and shape of the gel particles are crucial for specific applications. In this review, current methods of producing alginate gel particles will be discussed, taking into account their advantages, disadvantages, scalability, and impact on particle size. The physical properties of alginate gel particles will determine the effectiveness in different application conditions. This review will cover the current understanding of the alginate biopolymer, gelation mechanisms and factors affecting release properties, gel strength, and rheology of the alginate gel particle systems.

Innate Immune Signaling Activated by MDR Bacteria in the Airway

Health care-associated bacterial pneumonias due to multiple-drug resistant (MDR) pathogens are an important public health problem and are major causes of morbidity and mortality worldwide. In addition to antimicrobial resistance, these organisms have adapted to the milieu of the human airway and have acquired resistance to the innate immune clearance mechanisms that normally prevent pneumonia. Given the limited efficacy of antibiotics, bacterial clearance from the airway requires an effective immune response. Understanding how specific airway pathogens initiate and regulate innate immune signaling, and whether this response is excessive, leading to host-induced pathology may guide future immunomodulatory therapy. We will focus on three of the most important causes of health care-associated pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and review the mechanisms through which an inappropriate or damaging innate immune response is stimulated, as well as describe how airway pathogens cause persistent infection by evading immune activation.

Antimicrobial peptides and their interaction with biofilms of medically relevant bacteria

Biofilm-associated infections represent one of the major threats of modern medicine. Biofilm-forming bacteria are encased in a complex mixture of extracellular polymeric substances (EPS) and acquire properties that render them highly tolerant to conventional antibiotics and host immune response. Therefore, there is a pressing demand of new drugs active against microbial biofilms. In this regard, antimicrobial peptides (AMPs) represent an option taken increasingly in consideration. After dissecting the peculiar biofilm features that may greatly affect the development of new antibiofilm drugs, the present article provides a general overview of the rationale behind the use of AMPs against biofilms of medically relevant bacteria and on the possible mechanisms of AMP-antibiofilm activity. An analysis of the interactions of AMPs with biofilm components, especially those constituting the EPS, and the obstacles and/or opportunities that may arise from such interactions in the development of new AMP-based antibiofilm strategies is also presented and discussed. This article is part of a Special Issue entitled: Antimicrobial Peptides edited by Karl Lohner and Kai Hilpert.

Bifunctional silica nanoparticles for the exploration of biofilms of Pseudomonas aeruginosa

Luminescent silica nanoparticles are frequently employed for biotechnology applications mainly because of their easy functionalization, photo-stability, and biocompatibility. Bifunctional silica nanoparticles (BSNPs) are described here as new efficient tools for investigating complex biological systems such as biofilms. Photoluminescence is brought about by the incorporation of a silylated ruthenium(II) complex. The surface properties of the silica particles were designed by reaction with amino-organosilanes, quaternary ammonium-organosilanes, carboxylate-organosilanes and hexamethyldisilazane. BSNPs were characterized extensively by DRIFT, (13)C and (29)Si solid state NMR, XPS, and photoluminescence. Zeta potential and contact angle measurements exhibited various surface properties (hydrophilic/hydrophobic balance and electric charge) according to the functional groups. Confocal laser scanning microscopy (CLSM) measurements showed that the spatial distribution of these nanoparticles inside a biofilm of Pseudomonas aeruginosa PAO1 depends more on their hydrophilic/hydrophobic characteristics than on their size. CLSM observations using two nanosized particles (25 and 68 nm) suggest that narrow diffusion paths exist through the extracellular polymeric substances matrix.

Introduction of a lysine residue promotes aggregation of temporin L in lipopolysaccharides and augmentation of its antiendotoxin property

Temporin L (TempL) is a 13-residue frog antimicrobial peptide that shows moderate bactericidal activity and antiendotoxin properties in macrophages. We envisioned that, due to its very hydrophobic nature, the peptide might fail to show its desired biological properties. It was predicted by employing the available algorithms that the replacement of a glutamine by lysine at position 3 could appreciably reduce its aggregation propensity in an aqueous environment. In order to investigate the structural, functional, and biological consequences of replacement of glutamine by lysine at its third position, TempL and the corresponding analog, Q3K-TempL, was synthesized and characterized. Introduction of the lysine residue significantly promoted the self-assembly and oligomeric state of TempL in lipopolysaccharide (LPS). Q3K-TempL exhibited augmented binding to LPS and also dissociated LPS aggregates with greater efficacy than TempL. Further, Q3K-TempL inhibited the LPS-induced proinflammatory cytokines in rat primary macrophages in vitro and in vivo in BALB/c mice with greater efficacy than TempL. The results showed that a simple amino acid substitution in a short hydrophobic antimicrobial peptide, TempL, enhanced its antiendotoxin properties and illustrate a plausible correlation between its aggregation properties in LPS and LPS detoxification activity.

Extracellular DNA within a nontypeable Haemophilus influenzae-induced biofilm binds human beta defensin-3 and reduces its antimicrobial activity

Biofilms formed by nontypeable Haemophilus influenzae (NTHI) are associated with multiple chronic infections of the airway, including otitis media. Extracellular DNA (eDNA) is part of the biofilm matrix and serves as a structural component. Human β-defensin-3 (hBD-3) is a cationic antimicrobial host defense protein (AMP) critical to the protection of the middle ear. We hypothesized that anionic eDNA could interact with and bind hBD-3 and thus shield NTHI in biofilms from its antimicrobial activity. We demonstrated that recombinant hBD-3 [(r)hBD-3] bound eDNA in vitro and that eDNA in biofilms produced by NTHI in the chinchilla middle ear co-localized with the orthologue of this AMP. Incubation of physiological concentrations of (r)hBD-3 with NTHI genomic DNA abrogated the ability of this innate immune effector to prevent NTHI from forming robust biofilms in vitro. Establishment of NTHI biofilms in the presence of both DNase I and (r)hBD-3 resulted in a marked reduction in the overall height and thickness of the biofilms and rescued the antimicrobial activity of the AMP. Our results demonstrated that eDNA in NTHI biofilms sequestered hBD-3 and thus diminished the biological activity of an important effector of innate immunity. Our observations have important implications for chronicity of NTHI-induced diseases.

A novel approach combining the Calgary Biofilm Device and Phenotype MicroArray for the characterization of the chemical sensitivity of bacterial biofilms

A rapid method for screening the metabolic susceptibility of biofilms to toxic compounds was developed by combining the Calgary Biofilm Device (MBEC device) and Phenotype MicroArray (PM) technology. The method was developed using Pseudomonas alcaliphila 34, a Cr(VI)-hyper-resistant bacterium, as the test organism. P. alcaliphila produced a robust biofilm after incubation for 16 h, reaching the maximum value after incubation for 24 h (9.4 × 10(6) ± 3.3 × 10(6) CFU peg(-1)). In order to detect the metabolic activity of cells in the biofilm, dye E (5×) and menadione sodium bisulphate (100 μM) were selected for redox detection chemistry, because they produced a high colorimetric yield in response to bacterial metabolism (340.4 ± 6.9 Omnilog Arbitrary Units). This combined approach, which avoids the limitations of traditional plate counts, was validated by testing the susceptibility of P. alcaliphila biofilm to 22 toxic compounds. For each compound the concentration level that significantly lowered the metabolic activity of the biofilm was identified. Chemical sensitivity analysis of the planktonic culture was also performed, allowing comparison of the metabolic susceptibility patterns of biofilm and planktonic cultures.

Activity of antimicrobial peptides in the presence of polysaccharides produced by pulmonary pathogens

Antimicrobial peptides (AMPs) are secreted in the airway and contribute to initial defence against inhaled pathogens. Infections of the respiratory tract are a major cause of morbidity and mortality in preterm newborns and in patients with cystic fibrosis (CF). In this latter group, the state of chronic lung infection is due to the ability of bacteria to grow as mucoid biofilm, a condition characterised by overproduction and release of polysaccharides (PSs). In this study, we investigate the effect of PSs produced by lung pathogens such as Pseudomonas aeruginosa, Klebsiella pneumoniae and members of the Burkholderia cepacia complex on the antibacterial activity of structurally different peptides. The AMPs tested in this study include the cathelicidin LL-37 and the beta-defensin hBD-3 from humans, both released at the alveolar level, as well as peptides from other mammals, i.e. SMAP-29, PG-1 and Bac7(1-35). Susceptibility assays, time killing and membrane permeabilization kinetics experiments were carried out to establish whether PSs produced by lung pathogens may be involved in the poor defence reaction of infected lungs and thus explain infection persistence. All the PSs investigated inhibited, albeit to a different extent, the antibacterial activity of the peptides tested, suggesting that their presence in the lungs of patients with CF may contribute to the decreased defence response of this district upon infection by PS-producing microorganisms. The results also show that inhibition of the antibacterial activity is not simply due to ionic interaction between the negatively charged PSs and the cationic AMPs, but it also involves other structural features of both interactors.

Interactions between bovine serum albumin and alginate: an evaluation of alginate as protein carrier

The intermolecular interactions between the model protein, bovine serum albumin (BSA) and a biocompatible polysaccharide, sodium alginate, have been investigated. Both the native BSA and the heat pre-denatured BSA were utilized to study, in parallel, the effect of protein conformational change during the protein-alginate complex formation. In this work, a comparison was performed between the native BSA and the heat-denatured BSA incubated sodium alginate mixtures by using zeta potential analyzer, dynamic light scattering (DLS) and turbidimetric analysis of the systems in combination with protein conformational tools, Fourier transform infrared spectroscopy (FT-IR) and size exclusion chromatography (SE-HPLC). The experimental results demonstrate that the intermolecular chain associations were formed between alginate chains and protein molecules in either the native form or the heat pre-denatured form, mainly driven by the electrostatic interactions between the oppositely charged amino acids and the anionic polysaccharide macromolecules. However, the majority of BSA was recovered from the dissociation of protein-alginate complexes and maintained its secondary structure and conformational property. Therefore, alginate is promising as a bioactive compound carrier.

A study on the interactions of Aurein 2.5 with bacterial membranes

Aurein 2.5 (GLFDIVKKVVGAFGSL-NH(2)) is an uncharacterised antimicrobial peptide. At an air/water interface, it exhibited strong surface activity (maximal surface pressure 25mNm(-1)) and molecular areas consistent with the adoption of alpha-helical structure orientated either perpendicular (1.72nm(2)molecule(-1)) or parallel (3.6nm(2)molecule(-1)) to the interface. Aurein 2.5 was strongly antibacterial, exhibiting a minimum inhibitory concentration (MIC) of 30microM against Bacillus subtilis and Escherichia coli. The peptide induced maximal surface pressure changes of 9mNm(-1) and 5mNm(-1), respectively, in monolayers mimicking membranes of these organisms whilst compression isotherm analysis of these monolayers showed DeltaG(Mix)>0, indicating destabilisation by Aurein 2.5. These combined data suggested that toxicity of the peptide to these organisms may involve membrane invasion via the use of oblique orientated alpha-helical structure. The peptide induced strong, comparable maximal surface changes in monolayers of DOPG (7.5mNm(-1)) and DOPE monolayers (6mNm(-1)) suggesting that the membrane interactions of Aurein 2.5 were driven by amphiphilicity rather than electrostatic interaction. Based on these data, it was suggested that the differing ability of Aurein 2.5 to insert into membranes of B. subtilis and E. coli was probably related to membrane-based factors such as differences in lipid packing characteristics. The peptide was active against both sessile E. coli and Staphylococcus aureus with an MIC of 125microM. The broad-spectrum antibacterial activity and non-specific modes of membrane action used by Aurein 2.5 suggested use as an anti-biofilm agent such as in the decontamination of medical devices.