Engineered cationic antimicrobial peptide (eCAP) prevents Pseudomonas aeruginosa biofilm growth on airway epithelial cells

Innovations in the Isolation and Treatment of Biofilms in Periprosthetic Joint Infection: A Comprehensive Review of Current and Emerging Therapies in Bone and Joint Infection Management

Periprosthetic joint infections (PJIs) are a devastating complication of joint arthroplasty surgeries that are often complicated by biofilm formation. The development of biofilms makes PJI treatment challenging as they create a barrier against antibiotics and host immune responses. This review article provides an overview of the current understanding of biofilm formation, factors that contribute to their production, and the most common organisms involved in this process. This article focuses on the identification of biofilms, as well as current methodologies and emerging therapies in the management of biofilms in PJI.

In vitro and in vivo antibiofilm activity of the synthetic antimicrobial peptide WLBU2 against multiple drug resistant Pseudomonas aeruginosa strains

BACKGROUND

The global crisis of antibiotic resistance increases the demand for the novel promising alternative drugs such as antimicrobial peptides (AMPs). Here, the antibiofilm activity of the WLBU2 peptide against Pseudomonas aeruginosa (P. aeruginosa) isolates was investigated in this study.

METHODS

Two clinical MDR and carbapenem resistant P. aeruginosa (CRPA) isolates, and standard P. aeruginosa ATCC 27,853 were investigated. The MIC and MBC of WLBU2 were determined. The MBIC was determined to evaluate inhibitory activity of WLBU2 on biofilm formation and MBEC to dispersal activity on preformed biofilm. The relative expression levels of biofilm-associated genes including rhlI, rhlR, lasI and lasR were analyzed using RT-qPCR. In vivo evaluation of inhibitory effect of WLBU2 on biofilm formation was performed in the murine models of P. aeruginosa biofilm-associated subcutaneous catheter infection.

RESULTS

MIC and MBC of WLBU2 for both MDR and ATCC 27,853 P. aeruginosa strains were 8 and 16 µg/mL, respectively, while both the MIC and MBC against the CR strain were 4 µg/mL. MBIC was estimated to be 64 µg/ml for all strains. MBEC against MDR and ATCC 27,853- P. aeruginosa strains was 128 µg/ml and against CRPA was 64 µg/ml. The bacterial adhesion to a static abiotic solid surface (the surface in the polypropylene microtiter wells) was significantly inhibited at 1/4× MIC in all P. aeruginosa strains and at 1/8× MIC in CRPA strain (P < 0.05). Following treatment with WLBU2 at 1/8× MIC, significant inhibition in biofilm formation was observed in all isolates (P < 0.05). Results of the colorimetric assay showed that WLBU2 at 4× MIC was able to disperse 69.7% and 81.3% of pre-formed biofilms on abiotic surface produced by MDR and standard (ATCC 27,853) P. aeruginosa, respectively (P < 0.03), while a 92.2% reduction in the CRPA biofilm was observed after treatment with 4× MIC WLBU2 (P < 0.03). The expression levels of all genes in isolates treated with 1/2 MIC of WLBU2 were down-regulated by more than four-fold compared to the untreated isolates (P < 0.05). WLBU2 significantly inhibited biofilm formation in murine catheter-associated CRPA infection model at 1/4×MIC, 1/2×MIC, and 1×MIC by 33%, 52%, and 67%, respectively.

CONCLUSION

Considering relatively strong inhibitory and eradication potency of WLBU2 on the P. aeruginosa biofilms in in vitro and in vivo conditions, the peptide can be considered as a promising candidate for designing an antibiofilm drug.

Advances of Antimicrobial Peptide-Based Biomaterials for the Treatment of Bacterial Infections

Owing to the increase in multidrug-resistant bacterial isolates in hospitals globally and the lack of truly effective antimicrobial agents, antibiotic resistant bacterial infections have increased substantially. There is thus an urgent need to develop new antimicrobial drugs and their related formulations. In recent years, natural antimicrobial peptides (AMPs), AMP optimization, self-assembled AMPs, AMP hydrogels, and biomaterial-assisted delivery of AMPs have shown great potential in the treatment of bacterial infections. In this review, it is focused on the development prospects and shortcomings of various AMP-based biomaterials for treating animal model infections, such as abdominal, skin, and eye infections. It is hoped that this review will inspire further innovations in the design of AMP-based biomaterials for the treatment of bacterial infections and accelerate their commercialization.

Cystic fibrosis and primary ciliary dyskinesia: Similarities and differences

Cystic fibrosis (CF) and Primary ciliary dyskinesia (PCD) are both rare chronic diseases, inherited disorders associated with multiple complications, namely respiratory complications, due to impaired mucociliary clearance that affect severely patients' lives. Although both are classified as rare diseases, PCD has a much lower prevalence than CF, particularly among Caucasians. As a result, CF is well studied, better recognized by clinicians, and with some therapeutic approaches already available. Whereas PCD is still largely unknown, and thus the approach is based on consensus guidelines, expert opinion, and extrapolation from the larger evidence base available for patients with CF. Both diseases have some clinical similarities but are very different, necessitating different treatment by specialists who are familiar with the complexities of each disease.This review aims to provide an overview of the knowledge about the two diseases with a focus on the similarities and differences between both in terms of disease mechanisms, common clinical manifestations, genetics and the most relevant therapeutic options. We hoped to raise clinical awareness about PCD, what it is, how it differs from CF, and how much information is still lacking. Furthermore, this review emphasises the fact that both diseases require ongoing research to find better treatments and, in particular for PCD, to fill the medical and scientific gaps.

Antimicrobial Peptide Mechanism Studied by Scattering-Guided Molecular Dynamics Simulation

In an effort to combat rising antimicrobial resistance, our labs have rationally designed cationic, helical, amphipathic antimicrobial peptides (AMPs) as alternatives to traditional antibiotics since AMPs incur bacterial resistance in weeks, rather than days. One highly positively charged AMP, WLBU2 (+13e), (RRWV RRVR RWVR RVVR VVRR WVRR), has been shown to be effective in killing both Gram-negative (G(-)) and Gram-positive (G(+)) bacteria by directly perturbing the bacterial membrane nonspecifically. Previously, we used two equilibrium experimental methods: synchrotron X-ray diffuse scattering (XDS) providing lipid membrane thickness and neutron reflectometry (NR) providing WLBU2 depth of penetration into three lipid model membranes (LMMs). The purpose of the present study is to use the results from the scattering experiments to guide molecular dynamics (MD) simulations to investigate the detailed biophysics of the interactions of WLBU2 with LMMs of Gram-negative outer and inner membranes, and Gram-positive cell membranes, to elucidate the mechanisms of bacterial killing. Instead of coarse-graining, backmapping, or simulating without bias for several microseconds, all-atom (AA) simulations were guided by the experimental results and then equilibrated for ∼0.5 μs. Multiple replicas of the inserted peptide were run to probe stability and reach a combined time of at least 1.2 μs for G(-) and also 2.0 μs for G(+). The simulations with experimental comparisons help rule out certain structures and orientations and propose the most likely set of structures, orientations, and effects on the membrane. The simulations revealed that water, phosphates, and ions enter the hydrocarbon core when WLBU2 is positioned there. For an inserted peptide, the three types of amino acids, arginine, tryptophan, and valine (R, W, V), are arranged with the 13 Rs extending from the hydrocarbon core to the phosphate group, Ws are located at the interface, and Vs are more centrally located. For a surface state, R, W, and V are positioned relative to the bilayer interface as expected from their hydrophobicities, with Rs closest to the phosphate group, Ws close to the interface, and Vs in between. G(-) and G(+) LMMs are thinned ∼1 Å by the addition of WLBU2. Our results suggest a dual anchoring mechanism for WLBU2 both in the headgroup and in the hydrocarbon region that promotes a defect region where water and ions can flow across the slightly thinned bacterial cell membrane.

Treatment of Pseudomonas aeruginosa infectious biofilms: Challenges and strategies

Pseudomonas aeruginosa, a Gram-negative bacterium, is one of the major pathogens implicated in human opportunistic infection and a common cause of clinically persistent infections such as cystic fibrosis, urinary tract infections, and burn infections. The main reason for the persistence of P. aeruginosa infections is due to the ability of P. aeruginosa to secrete extracellular polymeric substances such as exopolysaccharides, matrix proteins, and extracellular DNA during invasion. These substances adhere to and wrap around bacterial cells to form a biofilm. Biofilm formation leads to multiple antibiotic resistance in P. aeruginosa, posing a significant challenge to conventional single antibiotic therapeutic approaches. It has therefore become particularly important to develop anti-biofilm drugs. In recent years, a number of new alternative drugs have been developed to treat P. aeruginosa infectious biofilms, including antimicrobial peptides, quorum-sensing inhibitors, bacteriophage therapy, and antimicrobial photodynamic therapy. This article briefly introduces the process and regulation of P. aeruginosa biofilm formation and reviews several developed anti-biofilm treatment technologies to provide new directions for the treatment of P. aeruginosa biofilm infection.

What Is New in the Anti–Pseudomonas aeruginosa Clinical Development Pipeline Since the 2017 WHO Alert?

The spread of antibiotic-resistant bacteria poses a substantial threat to morbidity and mortality worldwide. Carbapenem-resistant Pseudomonas aeruginosa (CRPA) are considered “critical-priority” bacteria by the World Health Organization (WHO) since 2017 taking into account criteria such as patient mortality, global burden disease, and worldwide trend of multi-drug resistance (MDR). Indeed P. aeruginosa can be particularly difficult to eliminate from patients due to its combinatory antibiotic resistance, multifactorial virulence, and ability to over-adapt in a dynamic way. Research is active, but the course to a validated efficacy of a new treatment is still long and uncertain. What is new in the anti–P. aeruginosa clinical development pipeline since the 2017 WHO alert? This review focuses on new solutions for P. aeruginosa infections that are in active clinical development, i.e., currently being tested in humans and may be approved for patients in the coming years. Among 18 drugs of interest in December 2021 anti–P. aeruginosa development pipeline described here, only one new combination of β-lactam/β-lactamase inhibitor is in phase III trial. Derivatives of existing antibiotics considered as “traditional agents” are over-represented. Diverse “non-traditional agents” including bacteriophages, iron mimetic/chelator, and anti-virulence factors are significantly represented but unfortunately still in early clinical stages. Despite decade of efforts, there is no vaccine currently in clinical development to prevent P. aeruginosa infections. Studying pipeline anti–P. aeruginosa since 2017 up to now shows how to provide a new treatment for patients can be a difficult task. Given the process duration, the clinical pipeline remains unsatisfactory leading best case to the approval of new antibacterial drugs that treat CRPA in several years. Beyond investment needed to build a robust pipeline, the Community needs to reinvent medicine with new strategies of development to avoid the disaster. Among “non-traditional agents”, anti-virulence strategy may have the potential through novel and non-killing modes of action to reduce the selective pressure responsible of MDR.

Evolved resistance to a novel cationic peptide antibiotic requires high mutation supply

Background and Objectives

A key strategy for resolving the antibiotic resistance crisis is the development of new drugs with antimicrobial properties. The engineered cationic antimicrobial peptide WLBU2 (also known as PLG0206) is a promising broad-spectrum antimicrobial compound that has completed Phase I clinical studies. It has activity against Gram-negative and Gram-positive bacteria including infections associated with biofilm. No definitive mechanisms of resistance to WLBU2 have been identified.

Methodology

Here, we used experimental evolution under different levels of mutation supply and whole genome sequencing (WGS) to detect the genetic pathways and probable mechanisms of resistance to this peptide. We propagated populations of wild-type and hypermutator Pseudomonas aeruginosa in the presence of WLBU2 and performed WGS of evolved populations and clones.

Results

Populations that survived WLBU2 treatment acquired a minimum of two mutations, making the acquisition of resistance more difficult than for most antibiotics, which can be tolerated by mutation of a single target. Major targets of resistance to WLBU2 included the orfN and pmrB genes, previously described to confer resistance to other cationic peptides. More surprisingly, mutations that increase aggregation such as the wsp pathway were also selected despite the ability of WLBU2 to kill cells growing in a biofilm.

Conclusions and implications

The results show how experimental evolution and WGS can identify genetic targets and actions of new antimicrobial compounds and predict pathways to resistance of new antibiotics in clinical practice.

Transferring Microclusters of P. aeruginosa Biofilms to the Air-Liquid Interface of Bronchial Epithelial Cells for Repeated Deposition of Aerosolized Tobramycin

As an alternative to technically demanding and ethically debatable animal models, the use of organotypic and disease-relevant human cell culture models may improve the throughput, speed, and success rate for the translation of novel anti-infectives into the clinic. Besides bacterial killing, host cell viability and barrier function appear as relevant but seldomly measured readouts. Moreover, bacterial virulence factors and signaling molecules are typically not addressed in current cell culture models. Here, we describe a reproducible protocol for cultivating barrier-forming human bronchial epithelial cell monolayers on Transwell inserts and infecting them with microclusters of pre-grown mature Pseudomonas aeruginosa PAO1 biofilms under the air-liquid interface conditions. Bacterial growth and quorum sensing molecules were determined upon tobramycin treatment. The host cell response was simultaneously assessed through cell viability, epithelial barrier function, and cytokine release. By repeated deposition of aerosolized tobramycin after 1, 24, and 48 h, bacterial growth was controlled (reduction from 10 to 4 log₁₀ CFU/mL), which leads to epithelial cell survival for up to 72 h. E-cadherin's cell-cell adhesion protein expression was preserved with the consecutive treatment, and quorum sensing molecules were reduced. However, the bacteria could not be eradicated and epithelial barrier function was impaired, similar to the currently observed situation in the clinic in lack of more efficient anti-infective therapies. Such a human-based in vitro approach has the potential for the preclinical development of novel anti-infectives and nanoscale delivery systems for oral inhalation.

The Engineered Antibiotic Peptide PLG0206 Eliminates Biofilms and Is a Potential Treatment for Periprosthetic Joint Infections

Antimicrobial peptides (AMPs) have recently gained attention for their potential to treat diseases related to bacterial and viral infections, as many traditional antimicrobial drugs have reduced efficacy in treating these infections due to the increased prevalence of drug-resistant pathogens. PLG0206, an engineered cationic antibiotic peptide that is 24 residues long, has been designed to address some limitations of other natural AMPs, such as toxicity and limited activity due to pH and ion concentrations. Nonclinical studies have shown that PLG0206 is highly selective for targeting bacterial cells and is not toxic to human blood cells. Antibiofilm experiments demonstrated that PLG0206 is effective at reducing both biotic and abiotic biofilm burdens following direct biofilm contact. PLG0206 has rapid and broad-spectrum activity against both Gram-positive and Gram-negative bacteria that are implicated as etiologic agents in periprosthetic joint infections, including multidrug-resistant ESKAPE pathogens and colistin-resistant isolates. A recent first-in-human study demonstrated that PLG0206 is well tolerated and safe as an intravenous infusion in healthy volunteers. Studies are planned to determine the efficacy of PLG0206 in patients for the treatment of periprosthetic joint infections. This review summarizes the chemistry, pharmacology, and microbiology of PLG0206 and explores its current preclinical, clinical, and regulatory status.

Synergism between WLBU2 peptide and antibiotics against methicillin-resistant Staphylococcus aureus and extended-spectrum beta-lactamase-producing Enterobacter cloacae

Infections caused by Methicillin-Resistant Staphylococcus aureus (MRSA) and Extended-Spectrum Beta-Lactamase (ESBL) producing Enterobacter cloacae are considered as major therapeutic challenge due to their multidrug-resistant (MDR) phenotype against conventional antibiotics. WLBU2 is an engineered cationic peptide with potent antimicrobial activity. This in-vitro study aimed to evaluate the effects of WLBU2 against clinical isolates of the aforementioned bacteria and assess whether synergistic effects can be achieved upon combination with conventional antibiotics. The minimum inhibitory concentrations (MICs) of antimicrobial agents against bacterial clinical isolates (n = 30/strain) were determined using the microbroth dilution assay. The minimum bactericidal concentrations (MBCs) of WLBU2 were determined from microbroth dilution (MICs) tests by subculturing to agar plates. MICs of WLBU2 were evaluated in the presence of physiological concentrations of salts including NaCl, CaCl2 and MgCl2. To identify bacterial resistance profile, MRSA were treated with Oxacillin, Erythromycin and Vancomycin, while Ceftazidime, Ceftriaxone, Ciprofloxacin and Imipenem were used against Enterobacter cloacae. Combination treatments of antibiotics and sub-inhibitory concentrations of WLBU2 were conducted when MICs indicated intermediate/resistant susceptibility. The MICs/MBCs of WLBU2 were identical for each respective bacteria with values of 0.78-6.25 μM and 1.5-12.5 μM against MRSA and Enterobacter cloacae, respectively. WLBU2 was found as salt resistant. Combination treatment showed that synergistic and additive effects were achieved in many isolates of MRSA and Enterobacter cloacae. Our data revealed that WLBU2 is a potent peptide with bactericidal activity. In addition, it demonstrated the selective advantage of WLBU2 as a potential therapeutic agent under physiological solutions. Our findings also support the combination of WLBU2 and conventional antibiotics with potential application for treatment of resistant bacteria.

Conjugation of Silver Nanoparticles with De Novo Engineered Cationic Antimicrobial Peptides: An Exploratory Proposal

Background

Cationic antimicrobial peptides have broad antimicrobial activity and provide a novel way of targeting multidrug-resistant bacteria in the era of increasing antimicrobial resistance. Current developments show positive prospects for antimicrobial peptides and silver nanoparticles (AgNPs) individually.

Objective

The primary objective is to propose another method for enhancing antimicrobial activity by conjugating AgNPs with cationic antimicrobial peptides, with a subsequent preliminary assessment of the minimum inhibitory concentration of multidrug-resistant bacteria. The secondary objective is to evaluate the safety of the conjugated compound and assess its viability for in vivo use.

Methods

The proposal involves 3 stages. First, WLBU2C, a modified version of the antimicrobial peptide WLBU2 with an added cysteine group, needs to be synthesized using a standard Fmoc procedure. It can then be stably conjugated with AgNPs ideally through photochemical means. Second, the WLBU2C-AgNP conjugate should be tested for antimicrobial activity according to the Clinical & Laboratory Standards Institute manual on standard minimum inhibitory concentration testing. Third, the cytotoxicity of the conjugate should be tested using cell lysis assays if the above stages are completed.

Results

I-TASSER (iterative threading assembly refinement) simulation revealed that the modified peptide WLBU2C has a secondary structure similar to that of the original WLBU2 peptide. No other results have been obtained at this time.

Conclusions

The addition of AgNPs to already developed de novo–engineered antimicrobial peptides provides an opportunity for the development of potent antimicrobials. Future prospects include emergency last-line therapy and treatment for current difficult-to-eradicate bacterial colonization, such as in cystic fibrosis, implantable medical devices, cancer, and immunotherapy. As I do not anticipate funding at this time, I hope this proposal provides inspiration to other researchers.

International Registered Report Identifier (IRRID)

PRR1-10.2196/28307

Peptide-Based Inhibitors for SARS-CoV-2 and SARS-CoV

The COVID‐19 (coronavirus disease) global pandemic, caused by the spread of the SARS‐CoV‐2 (severe acute respiratory syndrome coronavirus 2) virus, currently has limited treatment options which include vaccines, anti‐virals, and repurposed therapeutics. With their high specificity, tunability, and biocompatibility, small molecules like peptides are positioned to act as key players in combating SARS‐CoV‐2, and can be readily modified to match viral mutation rate. A recent expansion of the understanding of the viral structure and entry mechanisms has led to the proliferation of therapeutic viral entry inhibitors. In this comprehensive review, inhibitors of SARS and SARS‐CoV‐2 are investigated and discussed based on therapeutic design, inhibitory mechanistic approaches, and common targets. Peptide therapeutics are highlighted, which have demonstrated in vitro or in vivo efficacy, discuss advantages of peptide therapeutics, and common strategies in identifying targets for viral inhibition.

Bacterial Nosocomial Infections: Multidrug Resistance as a Trigger for the Development of Novel Antimicrobials

Nosocomial bacterial infections are associated with high morbidity and mortality, posing a huge burden to healthcare systems worldwide. The ongoing COVID-19 pandemic, with the raised hospitalization of patients and the increased use of antimicrobial agents, boosted the emergence of difficult-to-treat multidrug-resistant (MDR) bacteria in hospital settings. Therefore, current available antibiotic treatments often have limited or no efficacy against nosocomial bacterial infections, and novel therapeutic approaches need to be considered. In this review, we analyze current antibacterial alternatives under investigation, focusing on metal-based complexes, antimicrobial peptides, and antisense antimicrobial therapeutics. The association of new compounds with older, commercially available antibiotics and the repurposing of existing drugs are also revised in this work.

Air-liquid interface cultures of the healthy and diseased human respiratory tract: promises, challenges and future directions

Air-liquid interface (ALI) culture models currently represent a valid instrument to recreate the typical aspects of the respiratory tract in vitro in both healthy and diseased state. They can help reducing the number of animal experiments, therefore, supporting the 3R principle. This review discusses ALI cultures and co-cultures derived from immortalized as well as primary cells, which are used to study the most common disorders of the respiratory tract, in terms of both pathophysiology and drug screening. The article displays ALI models used to simulate inflammatory lung diseases such as chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis, lung cancer, and viral infections. It also includes a focus on ALI cultures described in literature studying respiratory viruses such as SARS-CoV-2 causing the global Covid-19 pandemic at the time of writing this review. Additionally, commercially available models of ALI cultures are presented. Ultimately, the aim of this review is to provide a detailed overview of ALI models currently available and to critically discuss them in the context of the most prevalent diseases of the respiratory tract.

Disease Models: Lung Models for Testing Drugs Against Inflammation and Infection

Lung diseases have increasingly attracted interest in the past years. The all-known fear of failing treatments against severe pulmonary infections and plans of the pharmaceutical industry to limit research on anti-infectives to a minimum due to cost reasons makes infections of the lung nowadays a "hot topic." Inhalable antibiotics show promising efficacy while limiting adverse systemic effects to a minimum. Moreover, in times of increased life expectancy in developed countries, the treatment of chronic maladies implicating inflammatory diseases, like bronchial asthma or chronic obstructive pulmonary disease, becomes more and more exigent and still lacks proper treatment.In this chapter, we address in vitro models as well as necessary in vivo models to help develop new drugs for the treatment of various severe pulmonary diseases with a strong focus on infectious diseases. By first presenting the essential hands-on techniques for the setup of in vitro models, we intend to combine these with already successful and interesting model approaches to serve as some guideline for the development of future models. The overall goal is to maximize time and cost-efficacy and to minimize attrition as well as animal trials when developing novel anti-infective therapeutics.

Antibiofilm peptides: overcoming biofilm-related treatment failure

Health leaders and scientists worldwide consider antibiotic resistance among the world's most dangerous pathogens as one of the biggest threats to global health. Antibiotic resistance has largely been attributed to genetic changes, but the role and recalcitrance of biofilms, largely due to growth state dependent adaptive resistance, is becoming increasingly appreciated. Biofilms are mono- and multi-species microbial communities embedded in an extracellular, protective matrix. In this growth state, bacteria are transcriptionally primed to survive extracellular stresses. Adaptations, affecting metabolism, regulation, surface charge, immune recognition and clearance, allow bacteria to thrive in the human body and withstand antibiotics and the host immune system. Biofilms resist clearance by multiple antibiotics and have a major role in chronic infections, causing more than 65% of all infections. No specific antibiofilm agents have been developed. Thus, there is a pressing need for alternatives to traditional antibiotics that directly inhibit and/or eradicate biofilms. Host defence peptides (HDPs) are small cationic peptides that are part of the innate immune system to both directly kill microbes but also function to modulate the immune response. Specific HDPs and their derivatives demonstrate broad-spectrum activity against biofilms. In vivo biofilm assays show efficacy in abscess, respiratory, in-dwelling device, contact lens and skin infection models. Further progress has been made through the study of ex vivo organoid and air-liquid interface models to better understand human infections and treatment while relieving the burden and complex nature of animal models. These avenues pave the way for a better understanding and treatment of the underlying cause of chronic infections that challenge the healthcare system.

Host defense peptide IDR-1002 associated with ciprofloxacin as a new antimicrobial and immunomodulatory strategy for dental pulp revascularization therapy

Regenerative therapies such as dental pulpal revascularization appear as an option for traumatized immature permanent teeth. However, the triple antibiotic paste - TAP (metronidazole, minocycline, and ciprofloxacin), used for these therapies, can generate cytotoxicity and dentin discoloration. In contrast, host defense peptides (HDPs) are promising antimicrobial and immunomodulatory biomolecules for dentistry. This study aimed to evaluate in vitro the antimicrobial activity (against Staphylococcus aureus and Enterococcus faecalis) and the immunomodulatory potential (by the evaluation of IL-1α, IL-6, IL-12, IL-10, TNF-α and NO, in RAW 264.7 macrophages and IL-6, TGF-β and NO, in L929 fibroblast) of synthetic peptides (DJK-6, IDR-1018, and IDR-1002), compared to TAP in an in vitro infection model containing heat-killed antigens from E. faecalis and S. aureus. Furthermore, the synergistic potential of ciprofloxacin and IDR-1002 was evaluated by checkerboard. Ciprofloxacin was the best antimicrobial of TAP, besides acting in synergism with IDR-1002. TAP was pro-inflammatory (p < 0.05), while the association of ciprofloxacin and IDR-1002 presented an anti-inflammatory profile mainly in the presence of both heat-killed antigens (p < 0.05). Based on these results, ciprofloxacin associated with IDR-1002 may demonstrate an efficient antimicrobial and immunomodulatory action in this in vitro model. Further in vivo studies may determine the real potential of this combination.

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.

A Novel Antimicrobial Peptide (Kassinatuerin-3) Isolated from the Skin Secretion of the African Frog, Kassina senegalensis

Amphibian skin secretions are remarkable sources of novel bioactive peptides. Among these, antimicrobial peptides have demonstrated an outstanding efficacy in killing microorganisms via a general membranolytic mechanism, which may offer the prospect of solving specific target-driven antibiotic resistance. Here, the discovery of a novel defensive peptide is described from the skin secretion of the African frog, Kassina senegalensis. Named kassinatuerin-3, it was identified through a combination of “shot-gun” cloning and MS/MS fragmentation sequencing. Subsequently, a synthetic replicate was subjected to biofunctional evaluation. The results indicated that kassinatuerin-3 possessed antimicrobial activity against Gram-positive bacteria but no effect against Gram-negative bacteria. Additionally, it was active in biofilm eradication on S. aureus and MRSA and in the antiproliferation of selected cancer cell lines. Moreover, it had a very mild hemolytic effect, which demonstrated a high therapeutic index for kassinatuerin-3. Collectively, although kassinatuerin-3 did not demonstrate remarkable bioactivities compared with other natural or synthetic antimicrobial peptides (AMPs), it offered a new insight into the design of antimicrobial derivatives.

Engineered Cationic Antimicrobial Peptides (eCAPs) to Combat Multidrug-Resistant Bacteria

The increasing rate of antibiotic resistance constitutes a global health crisis. Antimicrobial peptides (AMPs) have the property to selectively kill bacteria regardless of resistance to traditional antibiotics. However, several challenges (e.g., reduced activity in the presence of serum and lack of efficacy in vivo) to clinical development need to be overcome. In the last two decades, we have addressed many of those challenges by engineering cationic AMPs de novo for optimization under test conditions that typically inhibit the activities of natural AMPs, including systemic efficacy. We reviewed some of the most promising data of the last two decades in the context of the advancement of the field of helical AMPs toward clinical development.

Synergistic Biophysical Techniques Reveal Structural Mechanisms of Engineered Cationic Antimicrobial Peptides in Lipid Model Membranes

In the quest for new antibiotics, two novel engineered cationic antimicrobial peptides (eCAPs) have been rationally designed. WLBU2 and D8 (all 8 valines are the d-enantiomer) efficiently kill both Gram-negative and -positive bacteria, but WLBU2 is toxic and D8 nontoxic to eukaryotic cells. We explore protein secondary structure, location of peptides in six lipid model membranes, changes in membrane structure and pore evidence. We suggest that protein secondary structure is not a critical determinant of bactericidal activity, but that membrane thinning and dual location of WLBU2 and D8 in the membrane headgroup and hydrocarbon region may be important. While neither peptide thins the Gram-negative lipopolysaccharide outer membrane model, both locate deep into its hydrocarbon region where they are primed for self-promoted uptake into the periplasm. The partially α-helical secondary structure of WLBU2 in a red blood cell (RBC) membrane model containing 50 % cholesterol, could play a role in destabilizing this RBC membrane model causing pore formation that is not observed with the D8 random coil, which correlates with RBC hemolysis caused by WLBU2 but not by D8.

Antimicrobial peptides, an alternative to combat bacterial resistance

Antimicrobial peptides of higher organisms have been studied for the past 25 years, and their importance as components of innate immunity is now well established. The essential simplicity of their chemical structure, along with the lower likelihood of developed resistance compared to conventional antibiotics, has made them attractive candidates for development as therapeutics. The objective of this review article is to describe the current relevance, main mechanisms presented, and the uses of antimicrobial peptides as new therapies in the clinical area. The information used was mainly compiled from scientific articles based on a systematic review of scientific papers with data on human antimicrobial peptides (AMPs) and their different applications, searching without date limits and only documents in English and Spanish. Gray literature was accessed through manual search, and no restrictions were made involving study design for a retrospective study. Although these products have not yet been commercialized, they have advantages over the currently available treatments since they are not expected to cause bacterial resistance due to their three-dimensional structure, amphipathic tendency, and cationic character; however, the technique of peptide production is still new and is in the early stages of innovation of new molecules.

Combinations of early generation antibiotics and antimicrobial peptides are effective against a broad spectrum of bacterial biothreat agents

The misuse of infectious disease pathogens as agents of deliberate attack on civilians and military personnel is a serious national security concern, which is exacerbated by the emergence of natural or genetically engineered multidrug resistant strains. In this study, the therapeutic potential of combinations of an antibiotic and a broad-spectrum antimicrobial peptide (AMP) was evaluated against five bacterial biothreats, the etiologic agents of glanders (Burkholderia mallei), melioidosis (Burkholderia pseudomallei), plague (Yersinia pestis), tularemia (Francisella tularensis), and anthrax (Bacillus anthracis). The therapeutics included licensed early generation antibiotics which are now rarely used. Three antibiotics and one 24- amino acid AMP were selected based on MIC assay data. Combinations of the AMP and tigecycline, minocycline, or novobiocin were screened for synergistic activity by checkerboard MIC assay. The combinations each enhanced the susceptibility of several strains. The tetracycline-peptide combinations increased the sensitivities of Y. pestis, F. tularensis, B. anthracis and B. pseudomallei, and the novobiocin-AMP combination augmented the sensitivity of all five. In time-kill assays, down-selected combinations of the peptide and minocycline or tigecycline enhanced killing of B. anthracis, Y. pestis, F. tularensis, and Burkholderia mallei but not B. pseudomallei. The novobiocin-AMP pair significantly reduced viability of all strains except B. mallei, which was very sensitive to the antibiotic alone. The results suggested that antibiotic-AMP combinations are useful tools for combating diverse pathogens. Future studies employing cell culture and animal models will utilize virulent strains of the agents to investigate the in vivo availability, host cytotoxicity, and protective efficacy of these therapeutics.

Considerations and Caveats in Combating ESKAPE Pathogens against Nosocomial Infections

ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are among the most common opportunistic pathogens in nosocomial infections. ESKAPE pathogens distinguish themselves from normal ones by developing a high level of antibiotic resistance that involves multiple mechanisms. Contemporary therapeutic strategies which are potential options in combating ESKAPE bacteria need further investigation. Herein, a broad overview of the antimicrobial research on ESKAPE pathogens over the past five years is provided with prospective clinical applications.

Synergism of cationic antimicrobial peptide WLBU2 with antibacterial agents against biofilms of multi-drug resistant Acinetobacter baumannii and Klebsiella pneumoniae

Purpose

The activity of the cationic antimicrobial peptide WLBU2 was evaluated against planktonic cells and biofilms of multi-drug resistant (MDR) Acinetobacter baumannii and Klebsiella pneumoniae, alone and in combination with classical antimicrobial agents.

Methods

Control American Type Culture Collection (ATCC) strains and MDR clinical isolates of A. baumannii and K. pneumoniae were utilized. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of WLBU2 alone and in combination with antimicrobials were determined by classical methods. The Calgary biofilm device was used to determine the minimum biofilm eradication concentration (MBEC). The MTT assay was used to determine the cytotoxicity of agents on eukaryotic cells. The electrophoretic mobility shift assay was used to evaluate the ability of WLBU2 to bind bacterial DNA.

Results

The WLBU2 MIC and MBC values were identical indicating bactericidal activity. The MIC/MBC values ranged from 1.5625 to 12.5 µM. At these concentrations, Vero cells and human skin fibroblasts were viable. The MBEC of WLBU2 ranged from 25 to 200 µM. A significant loss of eukaryotic cell viability was observed at the MBEC range. The combination of sub-inhibitory concentrations of WLBU2 with amoxicillin-clavulanate or ciprofloxacin for K. pneumoniae, and with tobramycin or imipenem for A. baumannii, demonstrated synergism, leading to a significant decrease in MIC and MBEC values for some isolates and ATCC strains. However, all combinations were associated with considerable loss in eukaryotic cells’ viability. WLBU2 did not demonstrate the ability to bind bacterial plasmid DNA.

Conclusion

WLBU2 in combination with antimicrobials holds promise in eradication of MDR pathogens.

Pseudomonas aeruginosa Biofilms: Host Response and Clinical Implications in Lung Infections

Pseudomonas aeruginosa is a major health challenge that causes recalcitrant multidrug-resistant infections, especially in immunocompromised and hospitalized patients. P. aeruginosa is an important cause of nosocomial and ventilator-associated pneumonia characterized by high prevalence and fatality rates. P. aeruginosa also causes chronic lung infections in individuals with cystic fibrosis. Multidrug- and totally drug-resistant strains of P. aeruginosa are increasing threats that contribute to high mortality in these patients. The pathogenesis of many P. aeruginosa infections depends on its ability to form biofilms, structured bacterial communities that can coat mucosal surfaces or invasive devices. These biofilms make conditions more favorable for bacterial persistence, as embedded bacteria are inherently more difficult to eradicate than planktonic bacteria. The molecular mechanisms that underlie P. aeruginosa biofilm pathogenesis and the host response to P. aeruginosa biofilms remain to be fully defined. However, it is known that biofilms offer protection from the host immune response and are also extremely recalcitrant to antimicrobial therapy. Therefore, development of novel therapeutic strategies specifically aimed at biofilms is urgently needed. Here, we review the host response, key clinical implications of P. aeruginosa biofilms, and novel therapeutic approaches to treat biofilms relevant to lung infections. Greater understanding of P. aeruginosa biofilms will elucidate novel avenues to improve outcomes for P. aeruginosa pulmonary infections.

The Antimicrobial Peptide lin-SB056-1 and Its Dendrimeric Derivative Prevent Pseudomonas aeruginosa Biofilm Formation in Physiologically Relevant Models of Chronic Infections

Antimicrobial peptides (AMPs) are promising templates for the development of novel antibiofilm drugs. Despite the large number of studies on screening and optimization of AMPs, only a few of these evaluated the antibiofilm activity in physiologically relevant model systems. Potent in vitro activity of AMPs often does not translate into in vivo effectiveness due to the interference of the host microenvironment with peptide stability/availability. Hence, mimicking the complex environment found in biofilm-associated infections is essential to predict the clinical potential of novel AMP-based antimicrobials. In the present study, we examined the antibiofilm activity of the semi-synthetic peptide lin-SB056-1 and its dendrimeric derivative (lin-SB056-1)₂-K against Pseudomonas aeruginosa in an in vivo-like three-dimensional (3-D) lung epithelial cell model and an in vitro wound model (consisting of an artificial dermis and blood components at physiological levels). Although moderately active when tested alone, lin-SB056-1 was effective in reducing P. aeruginosa biofilm formation in association with 3-D lung epithelial cells in combination with the chelating agent EDTA. The dimeric derivative (lin-SB056-1)₂-K demonstrated an enhanced biofilm-inhibitory activity as compared to both lin-SB056-1 and the lin-SB056-1/EDTA combination, reducing the number of biofilm-associated bacteria up to 3-Log units at concentrations causing less than 20% cell death. Biofilm inhibition by (lin-SB056-1)₂-K was reported both for the reference strain PAO1 and cystic fibrosis lung isolates of P. aeruginosa. In addition, using fluorescence microscopy, a significant decrease in biofilm-like structures associated with 3-D cells was observed after peptide exposure. Interestingly, effectiveness of (lin-SB056-1)₂-K was also demonstrated in the wound model with a reduction of up to 1-Log unit in biofilm formation by P. aeruginosa PAO1 and wound isolates. Overall, combination treatment and peptide dendrimerization emerged as promising strategies to improve the efficacy of AMPs, especially under challenging host-mimicking conditions. Furthermore, the results of the present study underlined the importance of evaluating the biological properties of novel AMPs in in vivo-like model systems representative of specific infectious sites in order to make a more realistic prediction of their therapeutic success, and avoid the inclusion of unpromising peptides in animal studies and clinical trials.

AMPs as Anti-biofilm Agents for Human Therapy and Prophylaxis

Microbial cells show a strong natural tendency to adhere to surfaces and to colonize them by forming complex communities called biofilms. In this growth mode, biofilm-forming cells encase themselves inside a dense matrix which efficiently protects them against antimicrobial agents and effectors of the immune system. Moreover, at the physiological level, biofilms contain a very heterogeneous cell population including metabolically inactive organisms and persisters, which are highly tolerant to antibiotics. The majority of human infectious diseases are caused by biofilm-forming microorganisms which are responsible for pathologies such as cystic fibrosis, infective endocarditis, pneumonia, wound infections, dental caries, infections of indwelling devices, etc. AMPs are well suited to combat biofilms because of their potent bactericidal activity of broad spectrum (including resting cells and persisters) and their ability to first penetrate and then to disorganize these structures. In addition, AMPs frequently synergize with antimicrobial compounds and were recently reported to repress the molecular pathways leading to biofilm formation. Finally, there is a very active research to develop AMP-containing coatings that can prevent biofilm formation by killing microbial cells on contact or by locally releasing their active principle. In this chapter we will describe these strategies and discuss the perspectives of the use of AMPs as anti-biofilm agents for human therapy and prophylaxis.

Activity of a novel antimicrobial peptide against Pseudomonas aeruginosa biofilms

With the increasing recognition of biofilms in human disease, the development of novel antimicrobial therapies is of critical importance. For example, in patients with cystic fibrosis (CF), the acquisition of host-adapted, chronic Pseudomonas aeruginosa infection is associated with a decline in lung function and increased mortality. Our objective was to test the in vitro efficacy of a membrane-active antimicrobial peptide we designed, termed 6K-F17 (sequence: KKKKKK-AAFAAWAAFAA-NH₂), against multidrug resistant P. aeruginosa biofilms. This peptide displays high antimicrobial activity against a range of pathogenic bacteria, yet is non-hemolytic to human erythrocytes and non-toxic to human bronchial epithelial cells. In the present work, P. aeruginosa strain PAO1, and four multidrug resistant (MDR) isolates from chronically infected CF individuals, were grown as 48-hour biofilms in a static biofilm slide chamber model. These biofilms were then exposed to varying concentrations of 6K-F17 alone, or in the presence of tobramycin, prior to confocal imaging. Biofilm biovolume and viability were assessed. 6K-F17 was able to kill biofilms - even in the presence of sputum - and greatly reduce biofilm biovolume in PAO1 and MDR isolates. Strikingly, when used in conjunction with tobramycin, low doses of 6K-F17 significantly potentiated tobramycin killing, leading to biofilm destruction.

Enhanced biofilm prevention activity of a SPLUNC1-derived antimicrobial peptide against Staphylococcus aureus

SPLUNC1 is a multifunctional protein of the airway with antimicrobial properties. We previously reported that it displayed antibiofilm activities against P. aeruginosa. The goal of this study was to determine whether (1) the antibiofilm property is broad (including S. aureus, another prevalent organism in cystic fibrosis); (2) the α4 region is responsible for such activity; and (3), if so, this motif could be structurally optimized as an antimicrobial peptide with enhanced activities. We used S. aureus biofilm-prevention assays to determine bacterial biomass in the presence of SPLUNC1 and SPLUNC1Δα4 recombinant proteins, or SPLUNC1-derived peptides (α4 and α4M1), using the well-established crystal-violet biofilm detection assay. The SPLUNC1Δα4 showed markedly reduced biofilm prevention compared to the parent protein. Surprisingly, the 30-residue long α4 motif alone demonstrated minimal biofilm prevention activities. However, structural optimization of the α4 motif resulted in a modified peptide (α4M1) with significantly enhanced antibiofilm properties against methicillin–sensitive (MSSA) and–resistant (MRSA) S. aureus, including six different clinical strains of MRSA and the well-known USA300. Hemolytic activity was undetectable at up to 100μM for the peptides. The data warrant further investigation of α4-derived AMPs to explore the potential application of antimicrobial peptides to combat bacterial biofilm-related infections.

Design and Assessment of Anti-Biofilm Peptides: Steps Toward Clinical Application

Highly antibiotic resistant, microbial communities, referred to as biofilms, cause various life-threatening infections in humans. At least two-thirds of all clinical infections are biofilm associated, and antibiotic therapy regularly fails to cure patients. Anti-biofilm peptides represent a promising approach to treat these infections by targeting biofilm-specific characteristics such as highly conserved regulatory mechanisms. They are being considered for clinical application and we discuss here key factors in discovery, design, and application, particularly the implementation of host-mimicking conditions, that are required to enable the successful advancement of potent anti-biofilm peptides from the bench to the clinic.

Prevention of ESKAPE pathogen biofilm formation by antimicrobial peptides WLBU2 and LL37

OBJECTIVES

Bacterial biofilm-dependent infections (e.g. cystic fibrosis, surgical sites, and medical implants) are associated with enhanced drug-resistance and are thus difficult to eradicate. The goal of this study was to systematically compare three distinct classes of antimicrobial peptides (AMPs) that include the clinically used antibiotic colistin, the natural AMP LL37, the engineered cationic-AMP WLBU2, and four commonly used antibiotics with different bactericidal mechanisms (tobramycin, ciprofloxacin, ceftazidime, and vancomycin) for biofilm prevention properties.

METHODS

Using biofilm-prevention assays, we detected bacterial biomass post-attachment in subinhibitory concentrations (1/3 of the minimum inhibitory concentration [MIC]) for each AMP by the crystal violet method, to distinguish the commonly known bactericidal activity from potentially distinct mechanisms of biofilm prevention. Biofilm regulatory gene expression was assessed using RT-qPCR for correlation with biofilm growth inhibition.

RESULTS

Commonly used antibiotics at 1x MIC showed modest ESKAPE biofilm prevention while 1/3 MIC of AMPs demonstrated up to 90% biofilm prevention. WLBU2 was generally more effective in preventing bacterial attachment than colistin and LL37. Changes in bacterial biofilm regulatory gene expression were consistent with biofilm prevention.

CONCLUSION

The data warrant further exploration of AMPs with optimized structures to fill a knowledge gap on the potential application of AMPs for difficult-to-cure bacterial biofilm-related infections.

Elimination of Antibiotic Resistant Surgical Implant Biofilms Using an Engineered Cationic Amphipathic Peptide WLBU2

Antibiotics are unable to remove biofilms from surgical implants. This high antibiotic tolerance is related to bacterial persisters, a sub-population of bacteria phenotypically tolerant to antibiotics secondary to a reduced metabolic state. WLBU2 is an engineered cationic amphipathic peptide designed to maximize antimicrobial activity with minimal mammalian cell toxicity. The objective of this study was to test the ability of WLBU2 to remove Staphylococcus aureus surgical implant biofilms. WLBU2 effectively treated S. aureus biofilms formed by a variety of clinical MSSA and MRSA strains and created culture-negative implants in the in vitro biofilm model. Blocking bacterial metabolism by inhibiting oxidative phosphorylation did not affect WLBU2 killing compared to decreased killing by cefazolin. In the surgical implant infection animal model, WLBU2 decreased biofilm mass as compared to control, untreated samples. WLBU2 could rapidly eliminate implants in vitro and had sufficient efficacy in vivo with minimal systemic toxicity.

Antimicrobial Peptides: A Potential Therapeutic Option for Surgical Site Infections

Surgical Site Infections (SSI) represents one of the most common hospital-associated infections worldwide, and many cases of SSI are due to multidrug-resistant bacteria with the propensity to attach to tissues and form biofilm on post-surgical sites. While systemic antibiotic treatment (prophylactically and therapeutically) is usually effective, SSI can be difficult to treat when associated with drug resistance. Antimicrobial Peptides (AMPs) are an untapped resource that could serve as an effective therapeutic option, as they display broad-spectrum antimicrobial activity regardless of antibiotic resistance. In the last decade, it has become increasingly clear that AMPs also display antibiofilm properties. We reviewed herein the potential of AMPs as promising therapeutics for SSI and the need for structural optimization to develop AMPs for clinical applications.

Strategies for the etiological therapy of cystic fibrosis

Etiological therapies aim at repairing the underlying cause of cystic fibrosis (CF), which is the functional defect of the cystic fibrosis transmembrane conductance regulator (CFTR) protein owing to mutations in the CFTR gene. Among these, the F508del CFTR mutation accounts for more than two thirds of CF cases worldwide. Two somehow antinomic schools of thought conceive CFTR repair in a different manner. According to one vision, drugs should directly target the mutated CFTR protein to increase its plasma membrane expression (correctors) or improve its ion transport function (potentiators). An alternative strategy consists in modulating the cellular environment and proteostasis networks in which the mutated CFTR protein is synthesized, traffics to its final destination, the plasma membrane, and is turned over. We will analyze distinctive advantages and drawbacks of these strategies in terms of their scientific and clinical dimensions, and we will propose a global strategy for CF research and development based on a reconciliatory approach. Moreover, we will discuss the utility of preclinical biomarkers that may guide the personalized, patient-specific implementation of CF therapies.

Synthetic Arabinomannan Heptasaccharide Glycolipids Inhibit Biofilm Growth and Augment Isoniazid Effects in Mycobacterium smegmatis

Biofilm formation, involving attachment to an adherent surface, is a critical survival strategy of mycobacterial colonies in hostile environmental conditions. Here we report the synthesis of heptasaccharide glycolipids based on mannopyranoside units anchored on to a branched arabinofuranoside core. Two types of glycolipids-2,3-branched and 2,5-branched-were synthesized and evaluated for their efficacies in inhibiting biofilm growth by the non-pathogenic mycobacterium variant Mycobacterium smegmatis. Biofilm formation was inhibited at a minimum biofilm growth inhibition concentration (MBIC) of 100 μg mL^-1 in the case of the 2,5-branched heptasaccharide glycolipid. Further, we were able to ascertain that a combination of the drug isoniazid with the branched heptasaccharide glycolipid (50 μg mL^-1 ) potentiates the drug, making it three times more effective, with an improved MBIC of 30 μg mL^-1 . These studies establish that synthetic glycolipids not only act as inhibitors of biofilm growth, but also provide a synergistic effect when combined with significantly lowered concentrations of isoniazid to disrupt the biofilm structures of the mycobacteria.

Enhanced efficacy of the engineered antimicrobial peptide WLBU2 via direct airway delivery in a murine model of Pseudomonas aeruginosa pneumonia

OBJECTIVES

Pseudomonas aeruginosa is a common cause of pneumonia in patients with cystic fibrosis with the property to generate multidrug resistance against clinically used antibiotics. Antimicrobial peptides (AMPs) are a diverse group of effector molecules of the innate immune system that protect the host against pathogens. However, the lack of activity in common biological matrices has hampered efforts towards clinical development. In this study, we evaluated the therapeutic potential of the engineered AMP WLBU2 via direct airway delivery in a murine model of P. aeruginosa infection.

METHODS

The human AMPs LL37 and WLBU2 were compared for (i) antibiofilm activity using P. aeruginosa on polarized human bronchial epithelial cells, and (ii) efficacy in P. aeruginosa pneumonia in mice using intratracheal instillation of bacteria and AMPs.

RESULTS

WLBU2 (16 μM) prevents biofilm formation by up to 3-log compared with 1-log reduction by LL37. With a single dose of 1 μg (0.05 mg/kg) delivered intratracheally, the initial effect of LL37 was moderate and transitory, as bacterial load and inflammatory cytokines increased at 24 h with observed signs of disease such as lethargy and hypothermia, consistent with moribund state requiring euthanasia. In sharp contrast, WLBU2 reduced bacterial burden (by 2 logs) and bacteria-induced inflammation (leucocytic infiltrates, cytokine and chemokine gene expression) at 6 h and 24 h post-exposure, with no observed signs of disease or host toxicity.

CONCLUSION

These promising results now establish a much lower minimum therapeutic dose of WLBU2 (a net gain of 80-fold) compared with the previously reported 4 mg/kg systemic minimum therapeutic dose, with significant implications for clinical development.

Antimicrobial efficacy against Pseudomonas aeruginosa biofilm formation in a three-dimensional lung epithelial model and the influence of fetal bovine serum

In vitro models that mimic in vivo host-pathogen interactions are needed to evaluate candidate drugs that inhibit bacterial virulence traits. We established a new approach to study Pseudomonas aeruginosa biofilm susceptibility on biotic surfaces, using a three-dimensional (3-D) lung epithelial cell model. P. aeruginosa formed antibiotic resistant biofilms on 3-D cells without affecting cell viability. The biofilm-inhibitory activity of antibiotics and/or the anti-biofilm peptide DJK-5 were evaluated on 3-D cells compared to a plastic surface, in medium with and without fetal bovine serum (FBS). In both media, aminoglycosides were more efficacious in the 3-D cell model. In serum-free medium, most antibiotics (except polymyxins) showed enhanced efficacy when 3-D cells were present. In medium with FBS, colistin was less efficacious in the 3-D cell model. DJK-5 exerted potent inhibition of P. aeruginosa association with both substrates, only in serum-free medium. DJK-5 showed stronger inhibitory activity against P. aeruginosa associated with plastic compared to 3-D cells. The combined addition of tobramycin and DJK-5 exhibited more potent ability to inhibit P. aeruginosa association with both substrates. In conclusion, lung epithelial cells influence the efficacy of most antimicrobials against P. aeruginosa biofilm formation, which in turn depends on the presence or absence of FBS.

Beyond conventional antibiotics - New directions for combination products to combat biofilm

Medical device related infections are a significant and growing source of morbidity and mortality. Biofilm formation is a common feature of medical device infections that is not effectively prevented or treated by systemic antibiotics. Antimicrobial medical device combination products provide a pathway for local delivery of antimicrobial therapeutics with the ability to achieve high local concentrations while minimizing systemic side effects. In this review, we present considerations for the design of local antimicrobial delivery systems, which can be facilitated by modeling local pharmacokinetics in the context of the target device application. In addition to the need for local delivery, a critical barrier to progress in the field is the need to incorporate agents effective against biofilm. This article aims to review key properties of antimicrobial peptides that make them well suited to meet the demands of the next generation of antimicrobial medical devices, including broad spectrum activity, rapid and biocidal mechanisms of action, and efficacy against biofilm.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era.