A cathelicidin-2-derived peptide effectively impairs Staphylococcus epidermidis biofilms

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

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

DP1, a multifaceted synthetic peptide: Mechanism of action, activity and clinical potential

AIMS

Microbial infections remain a leading cause of mortality worldwide, with Staphylococcus aureus (S. aureus) being a prominent etiological agent, responsible for causing persistent bacterial infections in humans. It is a nosocomial, opportunistic pathogen, capable to propagate within the bloodstream and withstand therapeutic interventions. In the current study, a novel, indigenously designed synthetic antimicrobial peptide (sAMP) has been evaluated for its antimicrobial potential to inhibit the growth and proliferation of S. aureus.

MAIN METHODS

The sAMP, designed peptide (DP1) was evaluated for its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against a panel of pathogenic bacterial strains. Membrane mechanistic studies were performed by measuring membrane conductivity via dielectric spectroscopy and visualizing changes in bacterial membrane structure through field emission scanning electron microscopy (FE-SEM). Further, DP1 was tested for its in vivo antimicrobial potential in an S. aureus-induced systemic infection model.

KEY FINDINGS

The results indicated that DP1 has the potential to inhibit the growth and proliferation of a broad spectrum of Gram-positive, Gram-negative and multidrug-resistant (MDR) bacterial strains. Strong bactericidal effect attributed to change in electrical conductivity of the bacterial cells leading to membrane disruption was observed through dielectric spectroscopy and FE-SEM micrographs. Further, in the in vivo murine systemic infection study, 50 % reduction in S. aureus bioburden was observed within 1 day of the administration of DP1.

SIGNIFICANCE

The results indicate that DP1 is a multifaceted peptide with potent bactericidal, antioxidant and therapeutic properties. It holds significance as a novel drug candidate to effectively combat S. aureus-mediated systemic infections.

Design and Evaluation of a Novel Anti-microbial Peptide from Cathelicidin-2: Selectively Active Against Acinetobacter baumannii

Background

Infections caused by pathogenic microorganisms have increased the need for hospital care and have thus represented a public health problem and a significant financial burden. Classical treatments consisting of traditional antibiotics face several challenges today. Anti-microbial peptides (AMPs) are a conserved characteristic of the innate immune response among different animal species to defend against pathogenic microorganisms.

Objectives

In this study, a new peptide sequence (mCHTL131-140) was designed using the in silico approach.

Methods

Cathelicidin-2 (UniprotID: Q2IAL7) was used as a potential antimicrobial protein, and a novel 10 - 12 amino acids sequence AMP was designed using bioinformatics tools and the AMP databases. Then, the anti-bacterial, anti-biofilm, and anti-fungal properties of the peptide, as well as its hemolytic activity and cytotoxicity towards human fibroblast (HDF) cells, were investigated in vitro.

Results

Online bioinformatics tools indicated that the peptide sequence could have anti-bacterial, anti-viral, anti-fungal, and anti-biofilm properties with little hemolytic properties. The experimental tests confirmed that mCHTL131-140 exhibited the best anti-bacterial properties against Acinetobacter baumannii and had fair anti-fungal properties. Besides, it did not cause red blood cell lysis and showed no cytotoxicity towards HDF cells.

Conclusions

In general, the designed peptide can be considered a promising AMP to control hospital-acquired infections by A. baumannii.

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the "percutaneous device dilemma" in dental and other permanent implants

The percutaneous device dilemma describes etiological factors, centered around the disrupted epithelial tissue surrounding non-remodelable devices, that contribute to rampant percutaneous device infection. Natural percutaneous organs, in particular their extracellular matrix mediating the "device"/epithelium interface, serve as exquisite examples to inspire longer lasting long-term percutaneous device design. For example, the tooth's imperviousness to infection is mediated by the epithelium directly surrounding it, the junctional epithelium (JE). The hallmark feature of JE is formation of hemidesmosomes, cell/matrix adhesive structures that attach surrounding oral gingiva to the tooth's enamel through a basement membrane. Here, the authors survey the multifaceted functions of the JE, emphasizing the role of the matrix, with a particular focus on hemidesmosomes and their five main components. The authors highlight the known (and unknown) effects dental implant - as a model percutaneous device - placement has on JE regeneration and synthesize this information for application to other percutaneous devices. The authors conclude with a summary of bioengineering strategies aimed at solving the percutaneous device dilemma and invigorating greater collaboration between clinicians, bioengineers, and matrix biologists.

The Intracellular Interaction of Porcine β-Defensin 2 with VASH1 Alleviates Inflammation via Akt Signaling Pathway

Defensins are a major class of antimicrobial peptides that facilitate the immune system to resist pathogen infection. To date, only β-defensins have been identified in pigs. In our previous studies, porcine β-defensin 2 (PBD-2) was shown to have both bactericidal activity and modulatory roles on inflammation. PBD-2 can interact with the cell surface TLR4 and interfere with the NF-κB signaling pathway to suppress the inflammatory response. In this study, the intracellular functions of PBD-2 were investigated. The fluorescently labeled PBD-2 could actively enter mouse macrophage cells. Proteomic analysis indicated that 37 proteins potentially interacted with PBD-2, among which vasohibin-1 (VASH1) was further tested. LPS, an inflammation inducer, suppressed the expression of VASH1, whereas PBD-2 inhibited this effect. PBD-2 inhibited LPS-induced activation of Akt, expression and release of the inflammatory mediators vascular endothelial growth factor and NO, and cell damage. A follow-up VASH1 knockdown assay validated the specificity of the above observations. In addition, PBD-2 inhibited LPS-induced NF-κB activation via Akt. The inhibition effects of PBD-2 on LPS triggered suppression of VASH1 and activation of Akt, and NF-κB and inflammatory cytokines were also confirmed using pig alveolar macrophage 3D4/21 cells. Therefore, the data indicate that PBD-2 interacts with intracellular VASH1, which inhibits the LPS-induced Akt/NF-κB signaling pathway, resulting in suppression of inflammatory responses. Together with our previous findings, we conclude that PBD-2 interacts with both the cell surface receptor (TLR4) and also with the intracellular receptor (VASH1) to control inflammation, thereby providing insights into the immunomodulatory roles of defensins.

Antibacterial, Antibiofilm and Anti-Virulence Activity of Biactive Fractions from Mucus Secretion of Giant African Snail Achatina fulica against Staphylococcus aureus Strains

Staphylococcus aureus is an important etiological agent that causes skin infections, and has the propensity to form biofilms, leading to significant mortality and morbidity in patients with wounds. Mucus secretion from the Giant African snail Achatina fulica is a potential source of biologically active substances that might be an important source for new drugs to treat resistant and biofilm-forming bacteria such as S. aureus. This study evaluated the effect of semi-purified fractions from the mucus secretion of A. fulica on the growth, biofilm formation and virulence factors of S. aureus. Two fractions: FMA30 (Mw >30 kDa) and FME30 (Mw 30−10 kDa) exhibited antimicrobial activity against S. aureus with a MIC₅₀ of 25 and 125 µg/mL, respectively. An inhibition of biofilm formation higher than 80% was observed at 9 µg/mL with FMA30 and 120 µg/mL with FME30. Furthermore, inhibition of hemolytic and protease activity was determined using a concentration of MIC₂₀, and FME30 showed a strong inhibitory effect in the formation of clots. We report for the first time the effect of semi-purified fractions of mucus secretion of A. fulica on biofilm formation and activity of virulence factors such as α-hemolysin, coagulase and proteases produced by S. aureus strains.

Effect of Essential Oils on the Inhibition of Biofilm and Quorum Sensing in Salmonella enteritidis 13076 and Salmonella typhimurium 14028

The emergence of multidrug-resistant microorganisms represents a global challenge that has led to a search for new antimicrobial compounds. Essential oils (EOs) from medicinal aromatic plants are a potential alternative for conventional antibiotics. In this study, the antimicrobial and anti-biofilm potential of 15 EOs was evaluated on planktonic and biofilm-associated cells of Salmonella enterica serovar Enteritidis ATCC 13076 (S. enteritidis) and Salmonella enterica serovar Typhimurium ATCC 14028 (S. typhimurium). In total, 4 out of 15 EOs showed antimicrobial activity and 6 EOs showed anti-biofilm activity against both strains. The EO from the Lippia origanoides chemotype thymol-carvacrol II (LTC II) presented the lowest minimum inhibitory concentration (MIC₅₀ = 0.37 mg mL^-1) and minimum bactericidal concentration (MBC = 0.75 mg mL^-1) values. This EO also presented the highest percentage of biofilm inhibition (>65%) on both microorganisms, which could be confirmed by scanning electron microscopy (SEM) images. Transcriptional analysis showed significant changes in the expression of the genes related to quorum sensing and the formation of the biofilm. EOs could inhibit the expression of genes involved in the quorum sensing mechanism (luxR, luxS, qseB, sdiA) and biofilm formation (csgA, csgB, csgD, flhD, fliZ, and motB), indicating their potential use as anti-biofilm antimicrobial agents. However, further studies are needed to elucidate the action mechanisms of essential oils on the bacterial cells under study.

Anti-biofilm and anti-virulence effects of zerumbone against Acinetobacter baumannii

Acinetobacter baumannii is a multidrug-resistant opportunistic pathogen that affects patients with a compromised immune system and is becoming increasingly important as a hospital-derived infection. This pathogen is difficult to treat owing to its intrinsic multidrug resistance and ability to form antimicrobial-tolerant biofilms. In the present study, we aimed to assess the potential use of zerumbone as a novel anti-biofilm and/or anti-virulence agent against A. baumannii. The results showed that zerumbone at sub-inhibitory doses decreased biofilm formation and disrupted established A. baumannii biofilms. The zerumbone-induced decrease in biofilm formation was dose-dependent based on the results of microtitre plate biofilm assays and confocal laser scanning microscopy. In addition, our data validated the anti-virulence efficacy of zerumbone, wherein it significantly interfered with the motility of A. baumannii. To support these phenotypic results, transcriptional analysis revealed that zerumbone downregulated the expression of biofilm- and virulence-associated genes (adeA, adeB, adeC and bap) in A. baumannii. Overall, our findings suggested that zerumbone might be a promising bioactive agent for the treatment of biofilm- and virulence-related infections caused by multidrug-resistant A. baumannii.

Investigation of the effects of various stress factors on biofilms and planktonic bacteria in cooling tower model system

Biofilm is a microbial population which live in a self-produced extracellular polymeric matrix by attaching to surfaces. Biofilms consist of different different types of organisms such as bacteria, fungi, protozoa, etc. Many biofilms that develop in nature consist of more than one type of organism. Biofilms protect bacteria from adverse conditions such as temperature fluctuation and disinfectants. The aim of this study was to determine the effective elimination strategies for combating biofilm and planktonic bacteria in cooling tower model system using different decontamination / disinfection techniques. In this study, 14 week-old biofilms were treated with temperatures of 4 °C, 65 °C; pH of 3, 11; 2 and 10 mg/l chlorine, 2 and 10 mg/l monochloramine; hypotonic salt (0.01% NaCl) and hypertonic salt (3% NaCl) solution. For enumeration, number of aerobic heterotrophic bacteria was determined by conventional culture method, number of live bacteria was determined by LIVE/DEAD viability kit, CTC-DAPI and Alamar blue staining methods. Temperature of 65 °C, pH of 3, 10 mg/l monochloramine and hypertonic salt solution were the most effective parameters for decontamination of biofilm and planktonic bacteria. Biofilm bacteria in the circulating water system were significantly more resistant than planktonic bacteria against stress factors. When the numbers of epifluorescence microscopy and conventional culture technique were compared, significantly higher number of live bacteria were detected using epifluorescence microscopy. Bacteria enter the viable but non-culturable phase by loosing their culturability under stress conditions. For this reason, the conventional culture method should be supported by different techniques to get more realistic numbers.

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.

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Inhibitory effect of a novel chicken-derived anti-biofilm peptide on P. aeruginosa biofilms and virulence factors

The antibiotic resistance of Pseudomonas aeruginosa (P. aeruginosa) is correlated with the formation of biofilms. Several studies have focused on biofilms and the treatment of biofilm infection by antimicrobial peptides (AMPs). The present study analyzed the feasibility of cCATH-2 (a chicken-derived antimicrobial peptide) as a new strategy for anti-biofilm activities. Biofilm biomass (crystal violet staining) and viability of biofilm bacteria (colony counting) were measured in P. aeruginosa PAO1 biofilm at the stage of attachment (4 h), formation (14 h), and maturation (24 h). cCATH-2 (1/2MIC) had the ability to reduce the initial attachment of viable bacteria due to decreasing planktonic bacteria. All tested concentrations of cCATH-2 (1/32-1/2MIC) significantly reduced the biomass at the biofilm formation stage. In addition, cCATH-2 (2MIC) had significant effects on the biomass and viability of bacteria of pre-biofilms, which caused significant killing (>90%) of the bacteria in the biofilm. Thus, it was confirmed that cCATH-2 could infiltrate into pre-biofilm to kill the biofilm cells, as assessed by confocal laser scanning microscopy (CLSM). Furthermore, cCATH-2 had an obvious effect on the production of the majority of the virulence factors of PAO1 biofilms, and the effect was better than that of ciprofloxacin, especially on alginate (the structural component of biofilms). These findings suggested that cCATH-2 is a putative candidate for the development of anti-biofilm and anti-infective drugs.

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.

Anti-biofilm and Anti-Virulence Efficacy of Celastrol Against Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is a multi-drug resistant opportunistic pathogen that causes nosocomial infections in immunocompromised patients. This pathogen is difficult to treat owing to its intrinsic multidrug resistance and ability to form antimicrobial-tolerant biofilms. In the present study, we aimed to assess the potential use of celastrol as a novel anti-biofilm and/or anti-virulence agent against S. maltophilia. Results showed that celastrol at its sub-inhibitory doses decreased biofilm formation and disrupt the established biofilms produced by S. maltophilia. Celastrol-induced decrease in biofilm formation was dose-dependent based on the results of the microtiter plate biofilm assays and confocal laser scanning microscopy. In addition, our data validated the anti-virulence efficacy of celastrol, wherein it significantly interfered with the production of protease and motility of S. maltophilia. To support these phenotypic results, transcriptional analysis revealed that celastrol down-regulated the expression of biofilm- and virulence- associated genes (smeYZ, fsnR, and bfmAK) in S. maltophilia. Interestingly, celastrol significantly inhibited the expression of smeYZ gene, which encodes the resistance-nodulation-division (RND)-type efflux pump, SmeYZ. Overall, our findings suggested that celastrol might be a promising bioactive agent for treatment of biofilm- and virulence-related infections caused by the multi-drug resistant S. maltophilia.

Killing of Pseudomonas aeruginosa by Chicken Cathelicidin-2 Is Immunogenically Silent, Preventing Lung Inflammation In Vivo

The development of antibiotic resistance by Pseudomonas aeruginosa is a major concern in the treatment of bacterial pneumonia. In the search for novel anti-infective therapies, the chicken-derived peptide cathelicidin-2 (CATH-2) has emerged as a potential candidate, with strong broad-spectrum antimicrobial activity and the ability to limit inflammation by inhibiting Toll-like receptor 2 (TLR2) and TLR4 activation. However, as it is unknown how CATH-2 affects inflammation in vivo, we investigated how CATH-2-mediated killing of P. aeruginosa affects lung inflammation in a murine model. First, murine macrophages were used to determine whether CATH-2-mediated killing of P. aeruginosa reduced proinflammatory cytokine production in vitro Next, a murine lung model was used to analyze how CATH-2-mediated killing of P. aeruginosa affects neutrophil and macrophage recruitment as well as cytokine/chemokine production in the lung. Our results show that CATH-2 kills P. aeruginosa in an immunogenically silent manner both in vitro and in vivo Treatment with CATH-2-killed P. aeruginosa showed reduced neutrophil recruitment to the lung as well as inhibition of cytokine and chemokine production, compared to treatment with heat- or gentamicin-killed bacteria. Together, these results show the potential for CATH-2 as a dual-activity antibiotic in bacterial pneumonia, which can both kill P. aeruginosa and prevent excessive inflammation.

Anti-biofilm Activities from Resveratrol against Fusobacterium nucleatum

Fusobacterium nucleatum is a Gram-negative, anaerobic bacterium that plays an important role in dental plaque biofilm formation. In this study, we evaluate the effect of resveratrol, a phytoalexin compound, on F. nucleatum biofilm formation. The effects of different concentrations of resveratrol on biofilms formed on 96-well microtiter plates at different time points were determined by the MTT assay. The structures and thicknesses of the biofilm were observed by confocal laser scanning microscopy (CLSM), and gene expression was investigated by real-time PCR. The results showed that resveratrol at sub-MIC levels can significantly decrease biofilm formation, whereas it does not affect the bacterial growth rate. It was observed by CLSM images that the biofilm was visually decreased with increasing concentrations of resveratrol. Gene expression was down regulated in the biofilm in the presence of resveratrol. Our results revealed that resveratrol can effectively inhibit biofilm formation.

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.

In vitro and in vivo activity of the dimer of PMAP-36 expressed in Pichia pastoris

The antimicrobial peptide PMAP-36 exists as a homodimer stabilized by an intermolecular disulfide bridge. The dimer of PMAP-36 exhibits a potent and rapid microbicidal activity against a wide spectrum of microorganisms. The gene encoding the antiparallel dimer (PMAP-36)2 was designed and codon-optimized according to bias of Pichia pastoris. The gene was then expressed in the P. pastoris strain GS115. The concentration of the recombinant product reached 106 mg/l. In vitro activity assays indicated that the recombinant peptide showed antimicrobial activities against Gram-positive and Gram-negative bacteria but did not cause hemolysis of chicken erythrocytes. Subsequently, 120 7-day-old male Arbor Acres broilers were used to evaluate the in vivo activities of the peptide. A prophylactic dose of ciprofloxacin lactate was supplemented as the control. The results showed that recombinant (PMAP-36)2 significantly increased the serum IgM content of the birds (p < 0.05). The recombinant peptide significantly increased the amounts of Bifidobacterium and decreased the amount of Escherichia coli cells in the ceca of the experimental birds (p < 0.05). The results obtained in the present study indicate that the recombinant (PMAP-36)2 has a potent in vitro and in vivo activity and can be used as an alternative to antibiotic treatment.

The natural antimicrobial carvacrol inhibits quorum sensing in Chromobacterium violaceum and reduces bacterial biofilm formation at sub-lethal concentrations

The formation of biofilm by bacteria confers resistance to biocides and presents problems in medical and veterinary clinical settings. Here we report the effect of carvacrol, one of the major antimicrobial components of oregano oil, on the formation of biofilms and its activity on existing biofilms. Assays were carried out in polystyrene microplates to observe (a) the effect of 0–0.8 mM carvacrol on the formation of biofilms by selected bacterial pathogens over 24 h and (b) the effect of 0–8 mM carvacrol on the stability of pre-formed biofilms. Carvacrol was able to inhibit the formation of biofilms of Chromobacterium violaceum ATCC 12472, Salmonella enterica subsp. Typhimurium DT104, and Staphylococcus aureus 0074, while it showed no effect on formation of Pseudomonas aeruginosa (field isolate) biofilms. This inhibitory effect of carvacrol was observed at sub-lethal concentrations (<0.5 mM) where no effect was seen on total bacterial numbers, indicating that carvacrol's bactericidal effect was not causing the observed inhibition of biofilm formation. In contrast, carvacrol had (up to 8 mM) very little or no activity against existing biofilms of the bacteria described, showing that formation of the biofilm also confers protection against this compound. Since quorum sensing is an essential part of biofilm formation, the effect of carvacrol on quorum sensing of C. violaceum was also studied. Sub-MIC concentrations of carvacrol reduced expression of cviI (a gene coding for the N-acyl-L-homoserine lactone synthase), production of violacein (pigmentation) and chitinase activity (both regulated by quorum sensing) at concentrations coinciding with carvacrol's inhibiting effect on biofilm formation. These results indicate that carvacrol's activity in inhibition of biofilm formation may be related to the disruption of quorum sensing.

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.

Fungicidal mechanisms of cathelicidins LL-37 and CATH-2 revealed by live-cell imaging

Antifungal mechanisms of action of two cathelicidins, chicken CATH-2 and human LL-37, were studied and compared with the mode of action of the salivary peptide histatin 5 (Hst5). Candida albicans was used as a model organism for fungal pathogens. Analysis by live-cell imaging showed that the peptides kill C. albicans rapidly. CATH-2 is the most active peptide and kills C. albicans within 5 min. Both cathelicidins induce cell membrane permeabilization and simultaneous vacuolar expansion. Minimal fungicidal concentrations (MFC) are in the same order of magnitude for all three peptides, but the mechanisms of antifungal activity are very different. The activity of cathelicidins is independent of the energy status of the fungal cell, unlike Hst5 activity. Live-cell imaging using fluorescently labeled peptides showed that both CATH-2 and LL-37 quickly localize to the C. albicans cell membrane, while Hst5 was mainly directed to the fungal vacuole. Small amounts of cathelicidins internalize at sub-MFCs, suggesting that intracellular activities of the peptide could contribute to the antifungal activity. Analysis by flow cytometry indicated that CATH-2 significantly decreases C. albicans cell size. Finally, electron microscopy showed that CATH-2 affects the integrity of the cell membrane and nuclear envelope. It is concluded that the general mechanisms of action of both cathelicidins are partially similar (but very different from that of Hst5). CATH-2 has unique features and possesses antifungal potential superior to that of LL-37.

Avian host defense peptides

Host defense peptides (HDPs) are important effector molecules of the innate immune system of vertebrates. These antimicrobial peptides are also present in invertebrates, plants and fungi. HDPs display broad-spectrum antimicrobial activities and fulfill an important role in the first line of defense of many organisms. It is becoming increasingly clear that in the animal kingdom the functions of HDPs are not confined to direct antimicrobial actions. Research in mammals has indicated that HDPs have many immunomodulatory functions and are also involved in other physiological processes ranging from development to wound healing. During the past five years our knowledge about avian HDPs has increased considerably. This review addresses our current knowledge on the evolution, regulation and biological functions of HDPs of birds.

Cationic host defence peptides: multifaceted role in immune modulation and inflammation

Host defence peptides (HDPs) are innate immune effector molecules found in diverse species. HDPs exhibit a wide range of functions ranging from direct antimicrobial properties to immunomodulatory effects. Research in the last decade has demonstrated that HDPs are critical effectors of both innate and adaptive immunity. Various studies have hypothesized that the antimicrobial property of certain HDPs may be largely due to their immunomodulatory functions. Mechanistic studies revealed that the role of HDPs in immunity is very complex and involves various receptors, signalling pathways and transcription factors. This review will focus on the multiple functions of HDPs in immunity and inflammation, with special reference to cathelicidins, e.g. LL-37, certain defensins and novel synthetic innate defence regulator peptides. We also discuss emerging concepts of specific HDPs in immune-mediated inflammatory diseases, including the potential use of cationic peptides as therapeutics for immune-mediated inflammatory disorders.

New trends in peptide-based anti-biofilm strategies: a review of recent achievements and bioinformatic approaches

Antimicrobial peptides (AMPs) have a broad spectrum of activity and unspecific mechanisms of action. Therefore, they are seen as valid alternatives to overcome clinically relevant biofilms and reduce the chance of acquired resistance. This paper reviews AMPs and anti-biofilm AMP-based strategies and discusses ongoing and future work. Recent studies report successful AMP-based prophylactic and therapeutic strategies, several databases catalogue AMP information and analysis tools, and novel bioinformatics tools are supporting AMP discovery and design. However, most AMP studies are performed with planktonic cultures, and most studies on sessile cells test AMPs on growing rather than mature biofilms. Promising preliminary synergistic studies have to be consubstantiated and the study of functionalized coatings with AMPs must be further explored. Standardized operating protocols, to enforce the repeatability and reproducibility of AMP anti-biofilm tests, and automated means of screening and processing the ever-expanding literature are still missing.

Effects of cathelicidin and its fragments on three key enzymes of HIV-1

Cathelicidins exhibit anti-HIV activity but it is not known if they reduce the activity of enzymes crucial to the life cycle of the retrovirus. It is shown in this investigation that human cathelicidin LL37 and its fragments LL13-37 and LL17-32 inhibited HIV-1 reverse transcriptase dose-dependently with an IC50 value of 15μM, 7μM, and 70μM, respectively. The three peptides inhibited HIV-1 protease with a weak potency, achieving 20-30% inhibition at 100μM. The mechanism of inhibition was protein-protein interaction as revealed by surface plasmon resonance. The peptides were devoid of the ability to inhibit translocation of HIV-1 integrase, which has been labeled with green fluorescent protein, into the nucleus. The peptides did not exert toxicity on human peripheral blood mononuclear cells.