The interaction between Pseudomonas aeruginosa cells and cationic PC:Chol:DOTAP liposomal vesicles versus outer-membrane structure and envelope properties of bacterial cell

Inhaled antibiotics: A promising drug delivery strategies for efficient treatment of lower respiratory tract infections (LRTIs) associated with antibiotic resistant biofilm-dwelling and intracellular bacterial pathogens

Antibiotic-resistant bacteria associated with LRTIs are frequently associated with inefficient treatment outcomes. Antibiotic-resistant Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, and Staphylococcus aureus, infections are strongly associated with pulmonary exacerbations and require frequent hospital admissions, usually following failed management in the community. These bacteria are difficult to treat as they demonstrate multiple adaptational mechanisms including biofilm formation to resist antibiotic threats. Currently, many patients with the genetic disease cystic fibrosis (CF), non-CF bronchiectasis (NCFB) and chronic obstructive pulmonary disease (COPD) experience exacerbations of their lung disease and require high doses of systemically administered antibiotics to achieve meaningful clinical effects, but even with high systemic doses penetration of antibiotic into the site of infection within the lung is suboptimal. Pulmonary drug delivery technology that reliably deliver antibacterials directly into the infected cells of the lungs and penetrate bacterial biofilms to provide therapeutic doses with a greatly reduced risk of systemic adverse effects. Inhaled liposomal-packaged antibiotic with biofilm-dissolving drugs offer the opportunity for targeted, and highly effective antibacterial therapeutics in the lungs. Although the challenges with development of some inhaled antibiotics and their clinicals trials have been studied; however, only few inhaled products are available on market. This review addresses the current treatment challenges of antibiotic-resistant bacteria in the lung with some clinical outcomes and provides future directions with innovative ideas on new inhaled formulations and delivery technology that promise enhanced killing of antibiotic-resistant biofilm-dwelling bacteria.

β-lactam-induced OMV release promotes polymyxin tolerance in Salmonella enterica sv. Typhi

The rise of multidrug-resistant bacteria is a global concern, leading to a renewed reliance on older antibiotics like polymyxins as a last resort. Polymyxins, cationic cyclic peptides synthesized nonribosomally, feature a hydrophobic acyl tail and positively charged residues. Their antimicrobial mechanism involves initial interaction with Gram-negative bacterial outer-membrane components through polar and hydrophobic interactions. Outer membrane vesicles (OMVs), nano-sized proteoliposomes secreted from the outer membrane of Gram-negative bacteria, play a crucial role in tolerating harmful molecules, including cationic peptides such as polymyxins. Existing literature has documented environmental changes' impact on modulating OMV properties in Salmonella Typhimurium. However, less information exists regarding OMV production and characteristics in Salmonella Typhi. A previous study in our laboratory showed that S. Typhi ΔmrcB, a mutant associated with penicillin-binding protein (PBP, a β-lactam antibiotic target), exhibited hypervesiculation. Consequently, this study investigated the potential impact of β-lactam antibiotics on promoting polymyxin tolerance via OMVs in S. Typhi. Our results demonstrated that sub-lethal doses of β-lactams increased bacterial survival against polymyxin B in S. Typhi. This phenomenon stems from β-lactam antibiotics inducing hypervesiculation of OMVs with higher affinity for polymyxin B, capturing and diminishing its biologically effective concentration. These findings suggest that β-lactam antibiotic use may inadvertently contribute to decreased polymyxin effectivity against S. Typhi or other Gram-negative bacteria, complicating the effective treatment of infections caused by these pathogens. This study emphasizes the importance of evaluating the influence of β-lactam antibiotics on the interaction between OMVs and other antimicrobial agents.

Liposome-Based Antibacterial Delivery: An Emergent Approach to Combat Bacterial Infections

The continued emergence and spread of drug-resistant pathogens and the decline in the approval of new antimicrobial drugs pose a major threat to managing infectious diseases, resulting in high morbidity and mortality. Even though a significant variety of antibiotics can effectively cure many bacterial infectious diseases, microbial infections remain one of the biggest global health problems, which may be due to the traditional drug delivery system's shortcomings which lead to poor therapeutic index, low drug absorption, and numerous other drawbacks. Further, the use of traditional antibiotics to treat infectious diseases has always been accompanied by the emergence of multidrug resistance and adverse side effects. Despite developing numerous new antibiotics, nanomaterials, and various techniques to combat infectious diseases, they have persisted as major global health issues. Improving the current antibiotic delivery systems is a promising approach to solving many life-threatening infections. In this context, nanoliposomal systems have recently attracted much attention. Herein, we attempt to provide a concise summary of recent studies that have used liposomal nanoparticles as delivery systems for antibacterial medicines. The minireview also highlights the enormous potential of liposomal nanoparticles as antibiotic delivery systems. The future of these promising approaches lies in developing more efficient delivery systems by precisely targeting bacterial cells with antibiotics with minimum cytotoxicity and high bacterial combating efficacy.

Nanomaterials for Delivering Antibiotics in the Therapy of Pneumonia

Bacterial pneumonia is one of the leading causes of death worldwide and exerts a significant burden on health-care resources. Antibiotics have long been used as first-line drugs for the treatment of bacterial pneumonia. However, antibiotic therapy and traditional antibiotic delivery are associated with important challenges, including drug resistance, low bioavailability, and adverse side effects; the existence of physiological barriers further hampers treatment. Fortunately, these limitations may be overcome by the application of nanotechnology, which can facilitate drug delivery while improving drug stability and bioavailability. This review summarizes the challenges facing the treatment of bacterial pneumonia and also highlights the types of nanoparticles that can be used for antibiotic delivery. This review places a special focus on the state-of-the-art in nanomaterial-based approaches to the delivery of antibiotics for the treatment of pneumonia.

Designer Liposomic Nanocarriers Are Effective Biofilm Eradicators

Drug delivery via nanovehicles is successfully employed in several clinical settings, yet bacterial infections, forming microbial communities in the form of biofilms, present a strong challenge to therapeutic treatment due to resistance to conventional antimicrobial therapies. Liposomes can provide a versatile drug-vector strategy for biofilm treatment, but are limited by the need to balance colloidal stability with biofilm penetration. We have discovered a liposomic functionalization strategy, using membrane-embedded moieties of poly[2-(methacryloyloxy)ethyl phosphorylcholine], pMPC, that overcomes this limitation. Such pMPCylation results in liposomic stability equivalent to current functionalization strategies (mostly PEGylation, the present gold-standard), but with strikingly improved cellular uptake and cargo conveyance. Fluorimetry, cryo-electron, and fluorescence microscopies reveal a far-enhanced antibiotic delivery to model Pseudomonas aeruginosa biofilms by pMPC-liposomes, followed by faster cytosolic cargo release, resulting in significantly greater biofilm eradication than either PEGylation or free drug. Moreover, this combination of techniques uncovers the molecular mechanism underlying the enhanced interaction with bacteria, indicating it arises from bridging by divalent ions of the zwitterionic groups on the pMPC moieties to the negatively charged lipopolysaccharide chains emanating from the bacterial membranes. Our results point to pMPCylation as a transformative strategy for liposomal functionalization, leading to next-generation delivery systems for biofilm treatment.

Liposome-Encapsulated Tobramycin and IDR-1018 Peptide Mediated Biofilm Disruption and Enhanced Antimicrobial Activity against Pseudomonas aeruginosa

The inadequate eradication of pulmonary infections and chronic inflammation are significant complications in cystic fibrosis (CF) patients, who usually suffer from persistent and frequent lung infections caused by several pathogens, particularly Pseudomonas aeruginosa (P. aeruginosa). The ability of pathogenic microbes to protect themselves from biofilms leads to the development of an innate immune response and antibiotic resistance. In the present work, a reference bacterial strain of P. aeruginosa (PA01) and a multidrug-resistant isolate (MDR 7067) were used to explore the microbial susceptibility to three antibiotics (ceftazidime, imipenem, and tobramycin) and an anti-biofilm peptide (IDR-1018 peptide) using the minimum inhibition concentration (MIC). The most effective antibiotic was then encapsulated into liposomal nanoparticles and the IDR-1018 peptide with antibacterial activity, and the ability to disrupt the produced biofilm against PA01 and MDR 7067 was assessed. The MIC evaluation of the tobramycin antibacterial activity showed an insignificant effect on the liposomes loaded with tobramycin and liposomes encapsulating tobramycin and IDR-1018 against both P. aeruginosa strains to free tobramycin. Nevertheless, the biofilm formation was significantly reduced (p < 0.05) at concentrations of ≥4 μg/mL and ≤32 μg/mL for PA01 and ≤32 μg/mL for MDR 7067 when loading tobramycin into liposomes, with or without the anti-biofilm peptide compared to the free antibiotic, empty liposomes, and IDR-1018-loaded liposomes. A tobramycin concentration of ≤256 µg/mL was safe when exposed to a lung carcinoma cell line upon its encapsulation into the liposomal formulation. Tobramycin-loaded liposomes could be a potential candidate for treating lung-infected animal models owing to the high therapeutic efficacy and safety profile of this system compared to the free administration of the antibiotic.

Moxifloxacin Liposomes: Effect of Liposome Preparation Method on Physicochemical Properties and Antimicrobial Activity against Staphylococcus epidermidis

The aim of this study was the development of optimal sustained-release moxifloxacin (MOX)-loaded liposomes as intraocular therapeutics of endophthalmitis. Two methods were compared for the preparation of MOX liposomes; the dehydration–rehydration (DRV) method and the active loading method (AL). Numerous lipid-membrane compositions were studied to determine the potential effect on MOX loading and retention in liposomes. MOX and phospholipid contents were measured by HPLC and a colorimetric assay for phospholipids, respectively. Vesicle size distribution and surface charge were measured by DLS, and morphology was evaluated by cryo-TEM. The AL method conferred liposomes with higher MOX encapsulation compared to the DRV method for all the lipid compositions used. Cryo-TEM showed that both liposome types had round vesicular structure and size around 100–150 nm, while a granular texture was evident in the entrapped aqueous compartments of most AL liposomes, but substantially less in DRV liposomes; X-ray diffraction analysis demonstrated slight crystallinity in AL liposomes, especially the ones with highest MOX encapsulation. AL liposomes retained MOX for significantly longer time periods compared to DRVs. Lipid composition did not affect MOX release from DRV liposomes but significantly altered drug loading/release in AL liposomes. Interestingly, AL liposomes demonstrated substantially higher antimicrobial potential towards S. epidermidis growth and biofilm susceptibility compared to corresponding DRV liposomes, indicating the importance of MOX retention in liposomes on their activity. In conclusion, the liposome preparation method/type determines the rate of MOX release from liposomes and modulates their antimicrobial potential, a finding that deserves further in vitro and in vivo exploitation.

Targeting extracellular lectins of Pseudomonas aeruginosa with glycomimetic liposomes

The antimicrobial resistance crisis requires novel approaches for the therapy of infections especially with Gram-negative pathogens. Pseudomonas aeruginosa is defined as priority 1 pathogen by the WHO and thus of particular interest. Its drug resistance is primarily associated with biofilm formation and essential constituents of its extracellular biofilm matrix are the two lectins, LecA and LecB. Here, we report microbial lectin-specific targeted nanovehicles based on liposomes. LecA- and LecB-targeted phospholipids were synthesized and used for the preparation of liposomes. These liposomes with varying surface ligand density were then analyzed for their competitive and direct lectin binding activity. We have further developed a microfluidic device that allowed the optical detection of the targeting process to the bacterial lectins. Our data showed that the targeted liposomes are specifically binding to their respective lectin and remain firmly attached to surfaces containing these lectins. This synthetic and biophysical study provides the basis for future application in targeted antibiotic delivery to overcome antimicrobial resistance.

Combination and nanotechnology based pharmaceutical strategies for combating respiratory bacterial biofilm infections

Respiratory infections are one of the major global health problems. Among them, chronic respiratory infections caused by biofilm formation are difficult to treat because of both drug tolerance and poor drug penetration into the complex biofilm structure. A major part of the current research on combating respiratory biofilm infections have been focused on destroying the matrix of extracellular polymeric substance and eDNA of the biofilm or promoting the penetration of antibiotics through the extracellular polymeric substance via delivery technologies in order to kill the bacteria inside. There are also experimental data showing that certain inhaled antibiotics with simple formulations can effectively penetrate EPS to kill surficially located bacteria and centrally located dormant bacteria or persisters. This article aims to review recent advances in the pharmaceutical strategies for combating respiratory biofilm infections with a focus on nanotechnology-based drug delivery approaches. The formation and characteristics of bacterial biofilm infections in the airway mucus are presented, which is followed by a brief review on the current clinical approaches to treat respiratory biofilm infections by surgical removal and antimicrobial therapy, and also the emerging clinical treatment approaches. The current combination of antibiotics and non-antibiotic adjuvants to combat respiratory biofilm infections are also discussed.

Nanotechnology in combating biofilm: A smart and promising therapeutic strategy

Since the birth of civilization, people have recognized that infectious microbes cause serious and often fatal diseases in humans. One of the most dangerous characteristics of microorganisms is their propensity to form biofilms. It is linked to the development of long-lasting infections and more severe illness. An obstacle to eliminating such intricate structures is their resistance to the drugs now utilized in clinical practice (biofilms). Finding new compounds with anti-biofilm effect is, thus, essential. Infections caused by bacterial biofilms are something that nanotechnology has lately shown promise in treating. More and more studies are being conducted to determine whether nanoparticles (NPs) are useful in the fight against bacterial infections. While there have been a small number of clinical trials, there have been several in vitro outcomes examining the effects of antimicrobial NPs. Nanotechnology provides secure delivery platforms for targeted treatments to combat the wide range of microbial infections caused by biofilms. The increase in pharmaceuticals' bioactive potential is one of the many ways in which nanotechnology has been applied to drug delivery. The current research details the utilization of several nanoparticles in the targeted medication delivery strategy for managing microbial biofilms, including metal and metal oxide nanoparticles, liposomes, micro-, and nanoemulsions, solid lipid nanoparticles, and polymeric nanoparticles. Our understanding of how these nanosystems aid in the fight against biofilms has been expanded through their use.

Nano- and Macroscale Imaging of Cholesterol Linoleate and Human Beta Defensin 2-Induced Changes in Pseudomonas aeruginosa Biofilms

The biofilm production of Pseudomonas aeruginosa (PA) is central to establishing chronic infection in the airways in cystic fibrosis. Epithelial cells secrete an array of innate immune factors, including antimicrobial proteins and lipids, such as human beta defensin 2 (HBD2) and cholesteryl lineolate (CL), respectively, to combat colonization by pathogens. We have recently shown that HBD2 inhibits biofilm production by PA, possibly linked to interference with the transport of biofilm precursors. Considering that both HBD2 and CL are increased in airway fluids during infection, we hypothesized that CL synergizes with HBD2 in biofilm inhibition. CL was formulated in phospholipid-based liposomes (CL-PL). As measured by atomic force microscopy of single bacteria, CL-PL alone and in combination with HBD2 significantly increased bacterial surface roughness. Additionally, extracellular structures emanated from untreated bacterial cells, but not from cells treated with CL-PL and HBD2 alone and in combination. Crystal violet staining of the biofilm revealed that CL-PL combined with HBD2 effected a significant decrease of biofilm mass and increased the number of larger biofilm particles consistent with altered cohesion of formed biofilms. These data suggest that CL and HBD2 affect PA biofilm formation at the single cell and community-wide level and that the community-wide effects of CL are enhanced by HBD2. This research may inform future novel treatments for recalcitrant infections in the airways of CF patients.

Maltoheptaose-Presenting Nanoscale Glycoliposomes for the Delivery of Rifampicin to E. coli

Liposomes, a nanoscale drug delivery system, are well known for their ability to improve pharmacokinetics and reduce drug toxicity. In this work, maltoheptaose (G7)-presenting glycoliposomes were synthesized and evaluated in the delivery of the antibiotic rifampicin. Two types of liposomes were prepared: nonfluid liposomes from l-α-phosphatidylcholine (PC) and cholesterol, and fluid liposomes from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol). G7-derivatized glycolipid, G7-DPPE (DPPE: 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine), was incorporated into the liposomes at 21 and 14 μmol/mg to form nanoparticles of 75 ± 12 and 146 ± 14 nm for the nonfluid and fluid G7-glycoliposomes, respectively. The multivalent G7-glycoliposomes were characterized by lectin binding with concanavalin A (Con A). The dissociation constant K _d between Con A and the nonfluid or fluid G7-glycoliposomes was 0.93 or 0.51 μM, which represented ~900- or 1600-fold stronger affinity than the binding between Con A and G7. The G7-glycoliposomes were loaded with rifampicin at 6.6 and 16 wt % encapsulation for the nonfluid and fluid G7-glycoliposomes, respectively. Introducing a carbohydrate in the liposomes slowed down the release of rifampicin, with the G7-glycoliposomes having the slowest release rate and the lowest permeability coefficient among the liposome formulations. The fluid G7-glycoliposomes lowered the minimal inhibitory concentration (MIC) of rifampicin against E. coli ORN208 by about 3 times, whereas liposomes without G7 or Man (d-mannose)-glycoliposomes showed no improvement in MIC. The rifampicin-loaded fluid G7-glycoliposomes demonstrated the best sustained antibacterial activity against E. coli, with up to 2 log reduction in the colony forming units at 4 × MIC after 24 h. Fluorescence resonance energy transfer and confocal fluorescence microscopy revealed stronger interactions of the bacterium with the fluid G7-glycoliposomes than other liposome formulations.

Liposomes as Antibiotic Delivery Systems: A Promising Nanotechnological Strategy against Antimicrobial Resistance

Antimicrobial drugs are key tools to prevent and treat bacterial infections. Despite the early success of antibiotics, the current treatment of bacterial infections faces serious challenges due to the emergence and spread of resistant bacteria. Moreover, the decline of research and private investment in new antibiotics further aggravates this antibiotic crisis era. Overcoming the complexity of antimicrobial resistance must go beyond the search of new classes of antibiotics and include the development of alternative solutions. The evolution of nanomedicine has allowed the design of new drug delivery systems with improved therapeutic index for the incorporated compounds. One of the most promising strategies is their association to lipid-based delivery (nano)systems. A drug's encapsulation in liposomes has been demonstrated to increase its accumulation at the infection site, minimizing drug toxicity and protecting the antibiotic from peripheral degradation. In addition, liposomes may be designed to fuse with bacterial cells, holding the potential to overcome antimicrobial resistance and biofilm formation and constituting a promising solution for the treatment of potential fatal multidrug-resistant bacterial infections, such as methicillin resistant Staphylococcus aureus. In this review, we aim to address the applicability of antibiotic encapsulated liposomes as an effective therapeutic strategy for bacterial infections.

Liposomes-in-chitosan hydrogel boosts potential of chlorhexidine in biofilm eradication in vitro

Successful treatment of skin infections requires eradication of biofilms found in up to 90 % of all chronic wounds, causing delayed healing and increased morbidity. We hypothesized that chitosan hydrogel boosts the activity of liposomally-associated membrane active antimicrobials (MAA) and could potentially improve bacterial and biofilm eradication. Therefore, liposomes (∼300 nm) bearing chlorhexidine (CHX; ∼50 μg/mg lipid) as a model MAA were incorporated into chitosan hydrogel. The novel CHX-liposomes-in-hydrogel formulation was optimized for skin therapy. It significantly inhibited the production of nitric oxide (NO) in lipopolysaccharide (LPS)-induced macrophage and almost completely reduced biofilm formation. Moreover, it reduced Staphylococcus aureus and Pseudomonas aeruginosa adherent bacterial cells in biofilm by 64.2-98.1 %. Chitosan hydrogel boosted the anti-inflammatory and antimicrobial properties of CHX.

Liposome as a delivery system for the treatment of biofilm-mediated infections

Biofilm formation by pathogenic microorganisms has been a tremendous challenge for antimicrobial therapies due to various factors. The biofilm matrix sequesters bacterial cells from the exterior environment and therefore prevents antimicrobial agents from reaching the interior. In addition, biofilm surface extracellular polymeric substances can absorb antimicrobial agents and thus reduce their bioavailability. To conquer these protection mechanisms, liposomes have been developed into a drug delivery system for antimicrobial agents against biofilm-mediated infections. The unique characteristics of liposomes, including versatility for cargoes, target-specificity, nonimmunogenicity, low toxicity, and biofilm matrix-/cell membrane-fusogenicity, remarkably improve the effectiveness of antimicrobial agents and minimize recurrence of infections. This review summarizes current development of liposomal carriers for biofilm therapeutics, presents evidence in their practical applications and discusses their potential limitations.

Nanoparticulate drug-delivery systems for fighting microbial biofilms: from bench to bedside

Biofilms are highly tolerant to antimicrobial agents and adverse environmental conditions being important reservoirs for chronic and hard-to-treat infections. Nanomaterials exhibit microbiostatic/microbicidal/antipathogenic properties and can be also used for the delivery of antibiofilm agents. However, few of the many promising leads offered by nanotechnology reach clinical studies and eventually, become available to clinicians. The aim of this paper was to review the progress and challenges in the development of nanotechnology-based antibiofilm drug-delivery systems. The main identified challenges are: most papers report only in vitro studies of the activity of different nanoformulations; lack of standardization in the methodological approaches; insufficient collaboration between material science specialists and clinicians; paucity of in vivo studies to test efficiency and safety.

Cationic liposomes for generic signal amplification strategies in bioassays

Liposomes have been widely applied in bioanalytical assays. Most liposomes used bare negative charges to prevent non-specific binding and increase colloidal stability. Here, in contrast, highly stable, positively charged liposomes entrapping the fluorescent dye sulforhodamine B (SRB) were developed to serve as a secondary, non-specific label‚ and signal amplification tool in bioanalytical systems by exploiting their electrostatic interaction with negatively charged vesicles, surfaces, and microorganisms. The cationic liposomes were optimized for long-term stability (> 5 months) and high dye entrapment yield. Their capability as secondary, non-specific labels was first successfully proven through electrostatic interactions of cationic and anionic liposomes using dynamic light scattering, and then in a bioassay with fluorescence detection leading to an enhancement factor of 8.5 without any additional surface blocking steps. Moreover, the cationic liposomes bound efficiently to anionic magnetic beads were stable throughout magnetic separation procedures and could hence serve directly as labels in magnetic separation and purification strategies. Finally, the electrostatic interaction was exploited for the direct, simple, non-specific labeling of gram-negative bacteria. Isolated Escherichia coli cells were chosen as models and direct detection was demonstrated via fluorescent and chemiluminescent liposomes. Thus, these cationic liposomes can be used as generic labels for the development of ultrasensitive bioassays based on electrostatic interaction without the need for additional expensive recognition units like antibodies, where desired specificity is already afforded through other strategies.

Fusogenic Liposomes Increase the Antimicrobial Activity of Vancomycin Against Staphylococcus aureus Biofilm

Objective: The aim of the present study was to encapsulate vancomycin in different liposomal formulations and compare the in vitro antimicrobial activity against Staphylococcus aureus biofilms.

Methods: Large unilamellar vesicles of conventional (LUV VAN), fusogenic (LUV_fuso VAN), and cationic (LUV_cat VAN) liposomes encapsulating VAN were characterized in terms of size, polydispersity index, zeta potential, morphology, encapsulation efficiency (%EE) and in vitro release kinetics. The formulations were tested for their Minimum Inhibitory Concentration (MIC) and inhibitory activity on biofilm formation and viability, using methicillin-susceptible S. aureus ATCC 29213 and methicillin-resistant S. aureus ATCC 43300 strains.

Key Findings: LUV VAN showed better %EE (32.5%) and sustained release than LUV_fuso VAN, LUV_cat VAN, and free VAN. The formulations were stable over 180 days at 4°C, except for LUV VAN, which was stable up to 120 days. The MIC values for liposomal formulations and free VAN ranged from 0.78 to 1.56 µg/ml against both tested strains, with no difference in the inhibition of biofilm formation as compared to free VAN. However, when treating mature biofilm, encapsulated LUV_fuso VAN increased the antimicrobial efficacy as compared to the other liposomal formulations and to free VAN, demonstrating a better ability to penetrate the biofilm.

Conclusion: Vancomycin encapsulated in fusogenic liposomes demonstrated enhanced antimicrobial activity against mature S. aureus biofilms.

Nanomaterials and molecular transporters to overcome the bacterial envelope barrier: Towards advanced delivery of antibiotics

With the dramatic consequences of bacterial resistance to antibiotics, nanomaterials and molecular transporters have started to be investigated as alternative antibacterials or anti-infective carrier systems to improve the internalization of bactericidal drugs. However, the capability of nanomaterials/molecular transporters to overcome the bacterial cell envelope is poorly understood. It is critical to consider the sophisticated architecture of bacterial envelopes and reflect how nanomaterials/molecular transporters can interact with these envelopes, being the major aim of this review. The first part of this manuscript overviews the permeability of bacterial envelopes and how it limits the internalization of common antibiotic and novel oligonucleotide drugs. Subsequently we critically discuss the mechanisms that allow nanomaterials/molecular transporters to overcome the bacterial envelopes, focusing on the most promising ones to this end - siderophores, cyclodextrins, metal nanoparticles, antimicrobial/cell-penetrating peptides and fusogenic liposomes. This review may stimulate drug delivery and microbiology scientists in designing effective nanomaterials/molecular transporters against bacterial infections.

Azithromycin-loaded liposomes for enhanced topical treatment of methicillin-resistant Staphyloccocus aureus (MRSA) infections

Antibiotic delivery via liposomal encapsulation represents a promising approach for the efficient topical treatment of skin infections. The present study aimed to investigate the potential of using different types of azithromycin (AZT)-loaded liposomes to locally treat skin infections caused by methicillin-resistant Staphylococcus aureus (MRSA) strains. Conventional liposomes (CLs), deformable liposomes (DLs), propylene glycol-containing liposomes (PGLs) and cationic liposomes (CATLs) encapsulating AZT were prepared, and their physical characteristics, drug release profiles, ex vivo skin penetration/deposition abilities, in vitro anti-MRSA activities (planktonic bacteria and biofilm) and cell biocompatibilities were assessed. The (phospho)lipid composition and presence of surfactant or propylene glycol affected the physical characteristics of the liposomes, the release profile of AZT, its deposition inside the skin, as well as in vitro antibacterial efficacy and tolerability with the skin cells. All the liposomes retained AZT inside the skin more efficiently than did the control and were biocompatible with keratinocytes and fibroblasts. CATLs, DLs and PGLs efficiently inhibited MRSA strain growth and were superior to free AZT in preventing biofilm formation, exhibiting minimal inhibitory concentrations and minimal biofilm inhibitory concentrations up to 32-fold lower than those of AZT solution, thus confirming their potential for improved topical treatment of MRSA-caused skin infections.

Reducing Bacterial Infections and Biofilm Formation Using Nanoparticles and Nanostructured Antibacterial Surfaces

With the rapid spreading of resistance among common bacterial pathogens, bacterial infections, especially antibiotic-resistant bacterial infections, have drawn much attention worldwide. In light of this, nanoparticles, including metal and metal oxide nanoparticles, liposomes, polymersomes, and solid lipid nanoparticles, have been increasingly exploited as both efficient antimicrobials themselves or as delivery platforms to enhance the effectiveness of existing antibiotics. In addition to the emergence of widespread antibiotic resistance, of equal concern are implantable device-associated infections, which result from bacterial adhesion and subsequent biofilm formation at the site of implantation. The ineffectiveness of conventional antibiotics against these biofilms often leads to revision surgery, which is both debilitating to the patient and expensive. Toward this end, micro- and nanotopographies, especially those that resemble natural surfaces, and nonfouling chemistries represent a promising combination for long-term antibacterial activity. Collectively, the use of nanoparticles and nanostructured surfaces to combat bacterial growth and infections is a promising solution to the growing problem of antibiotic resistance and biofilm-related device infections.

A programmable lipid-polymer hybrid nanoparticle system for localized, sustained antibiotic delivery to Gram-positive and Gram-negative bacterial biofilms

Bacteria enmeshed in an extracellular matrix, biofilms, exhibit enhanced antibiotic tolerance. Coupled with the rapid emergence of multidrug-resistant strains, the current cohorts of antibiotics are becoming ineffective. Alternative antimicrobial approaches are therefore urgently needed to overcome recalcitrant biofilm infections. Here, we propose the use of a non-toxic lipid-polymer hybrid nanoparticle (LPN) system composed of a solid polymer core (i.e. PLGA; poly lactic-co-glycolic acid) and a cationic lipid shell (i.e. DOTAP) for localized, sustained release of antimicrobial agents to bacterial biofilms. LPNs were synthesized through a simple, robust self-assembly approach. LPNs of uniform particle size (i.e. 100-130 nm), efficiently encapsulated (up to 95%) bioimaging molecules or antibiotics and provided controlled release of the latter. The cationic lipid coating enabled the LPN to anchor onto surfaces of a diverse range of Gram-positive and Gram-negative bacterial pathogens, either in the planktonic or biofilm form. Consistently, the LPN formulations reduced more than 95% of biofilm activity at concentrations that were 8 to 32-fold lower than free antibiotics. These data clearly indicate that these novel formulations could be a useful strategy to enhance the efficacy of antimicrobials against planktonic cells and biofilms of diverse species.

Nanotechnology-based drug delivery systems for control of microbial biofilms: a review

Since the dawn of civilization, it has been understood that pathogenic microorganisms cause infectious conditions in humans, which at times, may prove fatal. Among the different virulent properties of microorganisms is their ability to form biofilms, which has been directly related to the development of chronic infections with increased disease severity. A problem in the elimination of such complex structures (biofilms) is resistance to the drugs that are currently used in clinical practice, and therefore, it becomes imperative to search for new compounds that have anti-biofilm activity. In this context, nanotechnology provides secure platforms for targeted delivery of drugs to treat numerous microbial infections that are caused by biofilms. Among the many applications of such nanotechnology-based drug delivery systems is their ability to enhance the bioactive potential of therapeutic agents. The present study reports the use of important nanoparticles, such as liposomes, microemulsions, cyclodextrins, solid lipid nanoparticles, polymeric nanoparticles, and metallic nanoparticles, in controlling microbial biofilms by targeted drug delivery. Such utilization of these nanosystems has led to a better understanding of their applications and their role in combating biofilms.

Antimicrobial molecules in the lung: formulation challenges and future directions for innovation

Inhaled antimicrobials have been extremely beneficial in treating respiratory infections, particularly chronic infections in a lung with cystic fibrosis. The pulmonary delivery of antibiotics has been demonstrated to improve treatment efficacy, reduce systemic side effects and, critically, reduce drug exposure to commensal bacteria compared with systemic administration, reducing selective pressure for antimicrobial resistance. This review will explore the specific challenges of pulmonary delivery of a number of differing antimicrobial molecules, and the formulation and technological approaches that have been used to overcome these difficulties. It will also explore the future challenges being faced in the development of inhaled products and respiratory infection treatment, and identify future directions of innovation, with a particular focus on respiratory infections caused by multiple drug-resistant pathogens.

Preparation of nano cationic liposome as carrier membrane for polyhexamethylene biguanide chloride through various methods utilizing higher antibacterial activities with low cell toxicity

This study suggested successful encapsulation of polyhexamethylene biguanide chloride (PHMB) into nano cationic liposome as a biocompatible antibacterial agent with less cytotoxicity and higher activities. Phosphatidylcholine, cholesterol and stearylamine were used to prepare nano cationic liposome using thin film hydration method along with sonication or homogeniser. Sonication was more effective in PHMB loaded nano cationic liposome preparation with smaller size (34 nm). FTIR, ¹H NMR and XRD analyses were used to confirm the encapsulation of PHMB into nano cationic liposome. PHMB inclusion in nano cationic liposome was beneficial for increased antibacterial activity against Staphylococcus aureus and Escherichia coli. PHMB-loaded cationic liposome enables to deliver high concentrations of the antibacterial agent into the infectious cell. The cytotoxicity of PHMB entrapped in positively charged liposome was prominently reduced showing no significant visible detrimental effect on normal primary human skin fibroblast cell lines morphology confirming the effective role of cationic liposome encapsulation. Comparing with PHMB alone, encapsulation of PHMB in nano cationic liposome resulted in significant increase in cell viability from 2.4 to 63%.

Recent Nanotechnology Approaches for Prevention and Treatment of Biofilm-Associated Infections on Medical Devices

Bacterial colonization in the form of biofilms on surfaces causes persistent infections and is an issue of considerable concern to healthcare providers. There is an urgent need for novel antimicrobial or antibiofilm surfaces and biomedical devices that provide protection against biofilm formation and planktonic pathogens, including antibiotic resistant strains. In this context, recent developments in the material science and engineering fields and steady progress in the nanotechnology field have created opportunities to design new biomaterials and surfaces with anti-infective, antifouling, bactericidal, and antibiofilm properties. Here we review a number of the recently developed nanotechnology-based biomaterials and explain underlying strategies used to make antibiofilm surfaces.

Current Trends in Development of Liposomes for Targeting Bacterial Biofilms

Biofilm targeting represents a great challenge for effective antimicrobial therapy. Increased biofilm resistance, even with the elevated concentrations of very potent antimicrobial agents, often leads to failed therapeutic outcome. Application of biocompatible nanomicrobials, particularly liposomally-associated nanomicrobials, presents a promising approach for improved drug delivery to bacterial cells and biofilms. Versatile manipulations of liposomal physicochemical properties, such as the bilayer composition, membrane fluidity, size, surface charge and coating, enable development of liposomes with desired pharmacokinetic and pharmacodynamic profiles. This review attempts to provide an unbiased overview of investigations of liposomes destined to treat bacterial biofilms. Different strategies including the recent advancements in liposomal design aiming at eradication of existing biofilms and prevention of biofilm formation, as well as respective limitations, are discussed in more details.

Inhaled formulations and pulmonary drug delivery systems for respiratory infections

Respiratory infections represent a major global health problem. They are often treated by parenteral administrations of antimicrobials. Unfortunately, systemic therapies of high-dose antimicrobials can lead to severe adverse effects and this calls for a need to develop inhaled formulations that enable targeted drug delivery to the airways with minimal systemic drug exposure. Recent technological advances facilitate the development of inhaled anti-microbial therapies. The newer mesh nebulisers have achieved minimal drug residue, higher aerosolisation efficiencies and rapid administration compared to traditional jet nebulisers. Novel particle engineering and intelligent device design also make dry powder inhalers appealing for the delivery of high-dose antibiotics. In view of the fact that no new antibiotic entities against multi-drug resistant bacteria have come close to commercialisation, advanced formulation strategies are in high demand for combating respiratory 'super bugs'.

Liposomal antibiotic formulations for targeting the lungs in the treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium that causes serious lung infections in cystic fibrosis, non-cystic fibrosis bronchiectasis, immunocompromised, and mechanically ventilated patients. The arsenal of conventional antipseudomonal antibiotic drugs include the extended-spectrum penicillins, cephalosporins, carbapenems, monobactams, polymyxins, fluoroquinolones, and aminoglycosides but their toxicity and/or increasing antibiotic resistance are of particular concern. Improvement of existing therapies against Pseudomonas aeruginosa infections involves the use of liposomes - artificial phospholipid vesicles that are biocompatible, biodegradable, and nontoxic and able to entrap and carry hydrophilic, hydrophobic, and amphiphilic molecules to the site of action. The goal of developing liposomal antibiotic formulations is to improve their therapeutic efficacy by reducing drug toxicity and/or by enhancing the delivery and retention of antibiotics at the site of infection. The focus of this review is to appraise the current progress of the development and application of liposomal antibiotic delivery systems for the treatment pulmonary infections caused by P. aeruginosa.

Improving the efficacy of inhaled drugs in cystic fibrosis: challenges and emerging drug delivery strategies

Cystic fibrosis (CF) is the most common autosomal recessive disease in Caucasians associated with early death. Although the faulty gene is expressed in epithelia throughout the body, lung disease is still responsible for most of the morbidity and mortality of CF patients. As a local delivery route, pulmonary administration represents an ideal way to treat respiratory infections, excessive inflammation and other manifestations typical of CF lung disease. Nonetheless, important determinants of the clinical outcomes of inhaled drugs are the concentration/permanence at the lungs as well as the ability of the drug to overcome local extracellular and cellular barriers. This review focuses on emerging delivery strategies used for local treatment of CF pulmonary disease. After a brief description of the disease and formulation rules dictated by CF lung barriers, it describes current and future trends in inhaled drugs for CF. The most promising advanced formulations are discussed, highlighting the advantages along with the major challenges for researchers working in this field.

Nano-antibiotics in chronic lung infection therapy against Pseudomonas aeruginosa

Antibiotic encapsulation into nanoparticle carriers has emerged as a promising inhaled antibiotic formulation for treatment of chronic Pseudomonas aeruginosa lung infection prevalent in chronic obstructive pulmonary diseases. Attributed to their prolonged lung retention, sustained antibiotic release, and mucus penetrating ability, antibiotic nanoparticles, or nano-antibiotics in short, can address the principal weakness of inhaled antibiotic solution, i.e. low antibiotic exposure in the vicinity of P. aeruginosa biofilm colonies resulting in diminished anti-pseudomonal efficacy after repeated uses. This review details the current state of development and limitations of the two most widely studied forms of nano-antibiotics, i.e. liposomes and polymer nanoparticles. Factors in their formulation that influence the anti-pseudomonal efficacy in vitro and in vivo, such as liposome's membrane rigidity, surface charge, size, and polymer hydrophobicity, are discussed. This review reveals that the superior anti-pseudomonal efficacy of liposomal antibiotics to free antibiotics has been clearly established when they are correctly formulated, with several liposomal antibiotic formulations are currently undergoing clinical trials. Liposomal antibiotics, nevertheless, are not without limitation due to their weak physicochemical stability. In contrast, only mucus penetrating ability of the more stable polymeric nano-antibiotics has been established, while their anti-pseudomonal efficacy has only been examined in vitro from which their superiority to free antibiotics has not been ascertained. Lastly, future research needs to bring liposome and polymer-based nano-antibiotics closer to their clinical realization are identified.

Nanoliposome-based antibacterial drug delivery

Although most bacterial infectious diseases can be treated successfully with the remarkable array of antibiotics, the microbial pathogens continue to be one of the most critical health challenges worldwide. One of the common efforts in addressing this issue lies in improving the existing antibacterial delivery systems since inefficient delivery can lead to poor therapeutic outcome of the administered drug. Recently, nanoliposomal systems have been widely used as promising strategies to overcome these challenges due to their unique set of properties. This article tries to briefly summarize the current studies that have taken advantage of liposomal nanoparticles as carriers to deliver antibacterial agents. The reviewed investigations demonstrate the immense potential of liposomal nanoparticles as carriers for antibiotic delivery and highlight the latent promise in this class of vehicles for treatment of bacterial infections. The future of these promising approaches lies in the development of more efficient techniques for preparing liposomal nanoparticles with great potential in effective and selective targeting of antibiotics to bacterial cells for eradication as well as the highest safety for human host.

Liposomal antibiotics for the treatment of infectious diseases

INTRODUCTION

Liposomal delivery systems have been utilized in developing effective therapeutics against cancer and targeting microorganisms in and out of host cells and within biofilm community. The most attractive feature of liposome-based drugs are enhancing therapeutic index of the new or existing drugs while minimizing their adverse effects.

AREAS COVERED

This communication provides an overview on several aspects of liposomal antibiotics including the most widely used preparation techniques for encapsulating different agents and the most important characteristic parameters applied for examining shape, size and stability of the spherical vesicles. In addition, the routes of administration, liposome-cell interactions and host parameters affecting the biodistribution of liposomes are highlighted.

EXPERT OPINION

Liposomes are safe and suitable for delivery of variety of molecules and drugs in biomedical research and medicine. They are known to improve the therapeutic index of encapsulated agents and reduce drug toxicity. Recent studies on liposomal formulation of chemotherapeutic and bioactive agents and their targeted delivery show liposomal antibiotics potential in the treatment of microbial infections.

Enhanced bactericidal potency of nanoliposomes by modification of the fusion activity between liposomes and bacterium

Background

Pseudomonas aeruginosa represents a good model of antibiotic resistance. These organisms have an outer membrane with a low level of permeability to drugs that is often combined with multidrug efflux pumps, enzymatic inactivation of the drug, or alteration of its molecular target. The acute and growing problem of antibiotic resistance of Pseudomonas to conventional antibiotics made it imperative to develop new liposome formulations to overcome these mechanisms, and investigate the fusion between liposome and bacterium.

Methods

The rigidity, stability and charge properties of phospholipid vesicles were modified by varying the cholesterol, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE), and negatively charged lipids 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol sodium salt (DMPG), 1,2-dimyristoyl-sn-glycero-3-phopho-L-serine sodium salt (DMPS), 1,2-dimyristoyl-sn-glycero-3-phosphate monosodium salt (DMPA), nature phosphatidylserine sodium salt from brain and nature phosphatidylinositol sodium salt from soybean concentrations in liposomes. Liposomal fusion with intact bacteria was monitored using a lipid-mixing assay.

Results

It was discovered that the fluid liposomes-bacterium fusion is not dependent on liposomal size and lamellarity. A similar degree of fusion was observed for liposomes with a particle size from 100 to 800 nm. The fluidity of liposomes is an essential pre-request for liposomes fusion with bacteria. Fusion was almost completely inhibited by incorporation of cholesterol into fluid liposomes. The increase in the amount of negative charges in fluid liposomes reduces fluid liposomes-bacteria fusion when tested without calcium cations due to electric repulsion, but addition of calcium cations brings the fusion level of fluid liposomes to similar or higher levels. Among the negative phospholipids examined, DMPA gave the highest degree of fusion, DMPS and DMPG had intermediate fusion levels, and PI resulted in the lowest degree of fusion. Furthermore, the fluid liposomal encapsulated tobramycin was prepared, and the bactericidal effect occurred more quickly when bacteria were cultured with liposomal encapsulated tobramycin.

Conclusion

The bactericidal potency of fluid liposomes is dramatically enhanced with respect to fusion ability when the fusogenic lipid, DOPE, is included. Regardless of changes in liposome composition, fluid liposomes-bacterium fusion is universally enhanced by calcium ions. The information obtained in this study will increase our understanding of fluid liposomal action mechanisms, and help in optimizing the new generation of fluid liposomal formulations for the treatment of pulmonary bacterial infections.

In vitro and in vivo activities of ticarcillin-loaded nanoliposomes with different surface charges against Pseudomonas aeruginosa (ATCC 29248)

Background

Pseudomonas aeruginosa exhibits multiple antibiotic resistance mechanisms. Different studies have shown that entrapment of antibiotics into liposomes could increase their anti-Pseudomonas activity. The objectives of this study were to prepare ticarcillin loaded-nanoliposomes with variable surface charges and evaluate their in vitro and in vivo efficacies against Pseudomonas aeruginosa (ATCC 29248).

Methods

Ticarcillin-loaded nanoliposomes with positive, negative and neutral surface charges were prepared by extrusion method. Ticarcillin encapsulation efficacies for different formulations were measured by HPLC method. Minimum inhibitory concentration (MIC) of ticarcillin nanoliposomal forms against strain ATCC 29248 were determined by broth dilution method. The killing rate of Pseudomonas aeruginosa was exposed to various concentrations of ticarcillin in free and nanoliposomal forms were analyzed. Ultimately, in vivo therapeutic efficacy of nanoliposomes in burned mice skin infected with strain ATCC 29248 was investigated.

Results

The encapsulation efficacies for ticarcillin-loaded cationic nanoliposomes were significantly higher (76% ± 0.17) than those of neutral (55% ± 0.14) and anionic (43% ± 0.14) nanoliposomes. The MIC of free, cationic, neutral and anionic nanoliposomal forms of ticarcillin against ATCC 29248 were to 24, 3, 6 and 48 mg/L, respectively. The killing rates of ticarcillin-loaded cationic nanoliposomes were higher than those of free and other drug formulations. Treatment by ticarcillin-loaded nanoliposomes with positive, neutral and negative surface charges resulted in almost 100, 60 and 20% survival rates, respectively.

Conclusion

Our data suggested that cationic ticarcillin-loaded nanoliposomes because of high effectiveness would be a good choice to treatment of Pseudomonas aeruginosa infections.

Preparation, characterization and in vitro antimicrobial activity of liposomal ceftazidime and cefepime against Pseudomonas aeruginosa strains

Pseudomonas aeruginosa is an opportunistic microorganism with the ability to respond to a wide variety of environmental changes, exhibiting a high intrinsic resistance to a number of antimicrobial agents. This low susceptibility to antimicrobial substances is primarily due to the low permeability of its outer membrane, efflux mechanisms and the synthesis of enzymes that promote the degradation of these drugs. Cephalosporins, particularty ceftazidime and cefepime are effective against P. aeruginosa, however, its increasing resistance has limited the usage of these antibiotics. Encapsulating antimicrobial drugs into unilamellar liposomes is an approach that has been investigated in order to overcome microorganism resistance. In this study, antimicrobial activity of liposomal ceftazidime and cefepime against P. aeruginosa ATCC 27853 and P. aeruginosa SPM-1 was compared to that of the free drugs. Liposomal characterization included diameter, encapsulation efficiency and stability. Minimum Inhibitory Concentration (MIC) was determined for free and liposomal forms of both drugs. Minimum Bactericidal Concentration (MBC) was determined at concentrations 1, 2 and 4 times MIC. Average diameter of liposomes was 131.88 nm and encapsulation efficiency for cefepime and ceftazidime were 2.29% end 5.77%, respectively. Improved stability was obtained when liposome formulations were prepared with a 50% molar ratio for cholesterol in relation to the phospholipid. MIC for liposomal antibiotics for both drugs were 50% lower than that of the free drug, demonstrating that liposomal drug delivery systems may contribute to increase the antibacterial activity of these drugs.