Mesoporous matrices for the delivery of the broad spectrum bacteriocin, nisin A

Bacteriocin diversity, function, discovery and application as antimicrobials

Bacteriocins are potent antimicrobial peptides that are produced by bacteria. Since their discovery almost a century ago, diverse peptides have been discovered and described, and some are currently used as commercial food preservatives. Many bacteriocins exhibit extensively post-translationally modified structures encoded on complex gene clusters, whereas others have simple linear structures. The molecular structures, mechanisms of action and resistance have been determined for a number of bacteriocins, but most remain incompletely characterized. These gene-encoded peptides are amenable to bioengineering strategies and heterologous expression, enabling metagenomic mining and modification of novel antimicrobials. The ongoing global antimicrobial resistance crisis demands that novel therapeutics be developed to combat infectious pathogens. New compounds that are target-specific and compatible with the resident microbiota would be valuable alternatives to current antimicrobials. As bacteriocins can be broad or narrow spectrum in nature, they are promising tools for this purpose. However, few bacteriocins have gone beyond preclinical trials and none is currently used therapeutically in humans. In this Review, we explore the broad diversity in bacteriocin structure and function, describe identification and optimization methods and discuss the reasons behind the lack of translation beyond the laboratory of these potentially valuable antimicrobials.

Bacteriocins: potentials and prospects in health and agrifood systems

Bacteriocins are highly diverse, abundant, and heterogeneous antimicrobial peptides that are ribosomally synthesized by bacteria and archaea. Since their discovery about a century ago, there has been a growing interest in bacteriocin research and applications. This is mainly due to their high antimicrobial properties, narrow or broad spectrum of activity, specificity, low cytotoxicity, and stability. Though initially used to improve food quality and safety, bacteriocins are now globally exploited for innovative applications in human, animal, and food systems as sustainable alternatives to antibiotics. Bacteriocins have the potential to beneficially modulate microbiota, providing viable microbiome-based solutions for the treatment, management, and non-invasive bio-diagnosis of infectious and non-infectious diseases. The use of bacteriocins holds great promise in the modulation of food microbiomes, antimicrobial food packaging, bio-sanitizers and antibiofilm, pre/post-harvest biocontrol, functional food, growth promotion, and sustainable aquaculture. This can undoubtedly improve food security, safety, and quality globally. This review highlights the current trends in bacteriocin research, especially the increasing research outputs and funding, which we believe may proportionate the soaring global interest in bacteriocins. The use of cutting-edge technologies, such as bioengineering, can further enhance the exploitation of bacteriocins for innovative applications in human, animal, and food systems.

Impact of carrier particle surface properties on drug nanoparticle attachment

HYPOTHESIS

The stabilization and isolation to dryness of drug nanoparticles has always been a challenge for nano-medicine production. In the past, the use of montmorillonite (MMT) clay carrier particles to adsorb drug nanoparticles and maintain their high surface area to volume ratio after isolation to dryness has proven to be effective. We hypothesise that the distribution of hydrophilic and hydrophobic patches on the clay's surface as well as its porosity/roughness, hinder the agglomeration of the drug nanoparticles to the extent that they retain their high surface area to volume ratio and display fast dissolution profiles.

EXPERIMENTS

In this work, the distribution of hydrophobicity and hydrophilicity, and the porosity/roughness, of the surface of selected silica carrier particles were varied and the impact of these variations on drug nanoparticle attachment to the carrier particle and subsequent dissolution profiles was studied.

FINDINGS

The fastest dissolution profiles at the highest drug nanoparticle loadings were obtained with a periodic mesoporous organosilane carrier particle which had a homogeneous distribution of hydrophobic and hydrophilic surface properties. Carrier particles with rough/porous surfaces and a combination of hydrophobic and hydrophilic patches resulted in nanocomposite powders with faster dissolution behaviour than carrier particles with predominantly either a hydrophobic or hydrophilic surface, or with non-porous/smoother surfaces.

Pre-formulation of an additive combination of two antimicrobial agents, clofazimine and nisin A, to boost antimicrobial activity

According to the World Health Organization, antimicrobial resistance is one of the top ten issues that pose a major threat to humanity. The lack of investment by the pharmaceutical industry has meant fewer novel antimicrobial agents are in development, exacerbating the problem. Emerging drug design strategies are exploring the repurposing of existing drugs and the utilization of novel drug candidates, like antimicrobial peptides, to combat drug resistance. This proactive approach is crucial in fighting global health threats. In this study, an additive combination of a repurposed anti-leprosy drug, clofazimine, and an antimicrobial peptide, nisin A, are preformulated using liquid antisolvent precipitation to generate a stable amorphous, ionized nanoparticle system to boost antimicrobial activity. The nanotechnology aims to improve the physicochemical properties of the inherently poorly water-soluble clofazimine molecules while also harnessing the previously unreported additive effect of clofazimine and nisin A. The approach transformed clofazimine into a more water-soluble salt, yielding amorphous nanoparticles stabilized by the antimicrobial peptide; and combined the two drugs into a more soluble and more active formulation. Blending pre-formulation strategies like amorphization, salt formation, and nanosizing to improve the inherent low aqueous solubility of drugs can open many new possibilities for the design of new antimicrobial agents. This fusion of pre-formulation technologies in combination with the multi-hurdle approach of selecting drugs with different effects on microbes could be key in the design platform of new antibiotics in the fight against antimicrobial resistance.

Pulmonary delivery systems for antimicrobial peptides

Bacterial infections of the respiratory tract cause millions of deaths annually. Several diseases exist wherein (1) bacterial infection is the main cause of disease (e.g., tuberculosis and bacterial pneumonia), (2) bacterial infection is a consequence of disease and worsens the disease prognosis (e.g., cystic fibrosis), and (3) bacteria-triggered inflammation propagates the disease (e.g., chronic obstructive pulmonary disease). Current approaches to combat infections generally include long and aggressive antibiotic treatments, which challenge patient compliance, thereby making relapses common and contributing to the development of antibiotic resistance. Consequently, the proportion of infections that cannot be treated with conventional antibiotics is rapidly increasing, and novel therapies are urgently needed. In this context, antimicrobial peptides (AMPs) have received considerable attention as they may exhibit potent antimicrobial effects against antibiotic-resistant bacterial strains but with modest toxicity. In addition, some AMPs suppress inflammation and provide other host defense functions (motivating the alternative term host defense peptides (HDPs)). However, the delivery of AMPs is complicated because they are large, positively charged, and amphiphilic. As a result of this, AMP delivery systems have recently attracted attention. For airway infections, the currently investigated delivery approaches range from aerosols and dry powders to various self-assembly and nanoparticle carrier systems, as well as their combinations. In this paper, we discuss recent developments in the field, ranging from mechanistic mode-of-action studies to the application of these systems for combating bacterial infections in the airways.

Very Large Pores Mesoporous Silica as New Candidate for Delivery of Big Therapeutics Molecules, Such as Pharmaceutical Peptides

The synthesis of a scaffold that can accommodate big molecules with a pharmaceutical role is important to shield them and maintain their biological activity. In this field, silica particles with large pores (LPMS) are innovative supports. Large pores allow for the loading of bioactive molecules inside the structure and contemporarily their stabilization and protection. These purposes cannot be achieved using classical mesoporous silica (MS, pore size 2-5 nm), because their pores are not big enough and pore blocking occurs. LPMSs with different porous structures are synthesized starting from an acidic water solution of tetraethyl orthosilicate reacting with pore agents (Pluronic^® F127 and mesitylene), performing hydrothermal and microwave-assisted reactions. Time and surfactant optimization were performed. Loading tests were conducted using Nisin as a reference molecule (polycyclic antibacterial peptide, with dimensions of 4-6 nm); UV-Vis analyses on loading solutions were performed. For LPMSs, a significantly higher loading efficiency (LE%) was registered. Other analyses (Elemental Analysis, Thermogravimetric Analysis and UV-Vis) confirmed the presence of Nisin in all the structures and its stability when loaded on them. LPMSs showed a lower decrease in specific surface area if compared to MS; in terms of the difference in LE% between samples, it is explained considering the filling of pores for LPMSs, a phenomenon that is not allowed for MSs. Release studies in simulated body fluid highlight, only for LPMSs, a controlled release, considering the longer time scale of release. Scanning Electron Microscopy images acquired before and after release tests shows the LPMSs' maintenance of the structure, demonstrating strength and mechanical resistance of structures. In conclusion, LPMSs were synthesized, performing time and surfactant optimization. LPMSs showed better loading and releasing properties with respect to classical MS. All collected data confirm a pore blocking for MS and an in-pore loading for LPMS.

A Review on the Adsorption Isotherms and Design Calculations for the Optimization of Adsorbent Mass and Contact Time

Adsorption is a widely used chemical engineering unit operation for the separation and purification of fluid streams. Typical uses of adsorption include the removal of targeted pollutants like antibiotics, dyes, heavy metals, and other small to large molecules from aqueous solutions or wastewater. To date several adsorbents that vary in terms of their physicochemical properties and costs have been tested for their efficacy to remove these pollutants from wastewater. Irrespective of the type of adsorbent, nature of the pollutant, or experimental conditions, the overall cost of adsorption depends directly on the adsorption contact time and the cost of the adsorbent materials. Thus, it is essential to minimize the amount of adsorbent and the contact time required. We carefully reviewed the attempts made by several researchers to minimize these two parameters using theoretical adsorption kinetics and isotherms. We also clearly explained the theoretical methods and the calculation procedures involved during the optimization of the adsorbent mass and the contact time. To complement the theoretical calculation procedures, we also made a detailed review on the theoretical adsorption isotherms that are commonly used to model experimental equilibrium data that can be used to optimize the adsorbent mass.

After a century of nisin research - where are we now?

It is almost a century since nisin was discovered in fermented milk cultures, coincidentally in the same year that penicillin was first described. Over the last 100 years this small, highly modified pentacyclic peptide has not only found success in the food industry as a preservative but has also served as the paradigm for our understanding of the genetic organization, expression, and regulation of genes involved in lantibiotic biosynthesis-one of the few cases of extensive post-translation modification in prokaryotes. Recent developments in understanding the complex biosynthesis of nisin have shed light on the cellular location of the modification and transport machinery and the co-ordinated series of spatio-temporal events required to produce active nisin and provide resistance and immunity. The continued unearthing of new natural variants from within human and animal gastrointestinal tracts has sparked interest in the potential application of nisin to influence the microbiome, given the growing recognition of the role the gastrointestinal microbiota plays in health and disease. Moreover, interdisciplinary approaches have taken advantage of biotechnological advancements to bioengineer nisin to produce novel variants and expand nisin functionality for applications in the biomedical field. This review will discuss the latest progress in these aspects of nisin research.

The impact of varying dextran oxidation levels on the inhibitory activity of a bacteriocin loaded injectable hydrogel

In the design of injectable antimicrobial dextran-alginate hydrogels, the impact of dextran oxidation and its subsequent changes in molecular weight and the incorporation of glycol chitosan on (i) gel mechanical strength and (ii) the inhibitory profile of an encapsulated bacteriocin, nisin A, are explored. As the degree of oxidation increases, the weight average molecular mass of the dextran decreases, resulting in a reduction in elastic modulus of the gels made. Upon encapsulation of the bacteriocin nisin into the gels, varying the dextran mass/oxidation level allowed the antimicrobial activity against S. aureus to be controlled. Gels made with a higher molecular weight (less oxidised) dextran show a higher initial degree of inhibition while those made with a lower molecular weight (more oxidised) dextran exhibit a more sustained inhibition. Incorporating glycol chitosan into gels composed of dextran with higher masses significantly increased their storage modulus and the gels' initial degree of inhibition.

Synergistic antimicrobial interactions of nisin A with biopolymers and solubilising agents for oral drug delivery

In order to develop bacteriocins, like the lantibiotic nisin A, into effective alternatives to existing antibiotics, their biophysical and physicochemical properties must first be assessed, from solubility, to susceptibility and absorption. It has been well established that formulation strategies at early drug development stages can be crucial for successful outcomes during preclinical and clinical phases of development, particularly for molecules with challenging physicochemical properties. This work elucidates the physicochemical challenges of nisin A in terms of its susceptibility to digestive enzymes like pepsin, pancreatin and proteinase K and its poor solubility at physiological pHs. Low solution concentrations, below the minimum inhibitory concentration against Staphylococcus aureus, were obtained in phosphate buffered saline (PBS, pH 7.4) and in fasted state simulated intestinal fluid (FaSSIF, pH 6.5), while higher solubilities at more acidic pH's such as in a KCl/HCl buffer (pH 2) and in fasted state simulated gastric fluid (FaSSGF, pH 1.6) are observed. Tween® 80 (0.01% v/v) significantly increased the solution concentration of nisin A in PBS (pH 7.4, 24 hr). Pancreatin doubled nisin A's solution concentration at pH 7.4 (PBS) but reduced its' inhibitory activity to ∼ 20%, and pepsin almost completely degraded nisin (after 24 hr), but retained activity at biologically relevant exposure times (∼ 15 min). Harnessing synergism between nisin A and either glycol chitosan or ε-poly lysine, combined with the solubilizing effect of Tween®, increased the antimicrobial activity of nisin A six fold in an in vitro oral administration model.

Membrane-disruptive peptides/peptidomimetics-based therapeutics: Promising systems to combat bacteria and cancer in the drug-resistant era

Membrane-disruptive peptides/peptidomimetics (MDPs) are antimicrobials or anticarcinogens that present a general killing mechanism through the physical disruption of cell membranes, in contrast to conventional chemotherapeutic drugs, which act on precise targets such as DNA or specific enzymes. Owing to their rapid action, broad-spectrum activity, and mechanisms of action that potentially hinder the development of resistance, MDPs have been increasingly considered as future therapeutics in the drug-resistant era. Recently, growing experimental evidence has demonstrated that MDPs can also be utilized as adjuvants to enhance the therapeutic effects of other agents. In this review, we evaluate the literature around the broad-spectrum antimicrobial properties and anticancer activity of MDPs, and summarize the current development and mechanisms of MDPs alone or in combination with other agents. Notably, this review highlights recent advances in the design of various MDP-based drug delivery systems that can improve the therapeutic effect of MDPs, minimize side effects, and promote the co-delivery of multiple chemotherapeutics, for more efficient antimicrobial and anticancer therapy.

Adsorption of Recombinant Human β-Defensin 2 and Two Mutants on Mesoporous Silica Nanoparticles and Its Effect against Clavibacter michiganensis subsp. michiganensis

Solanum lycopersicum L. is affected among other pests and diseases, by the actinomycete Clavibacter michiganensis subsp. michiganensis (Cmm), causing important economic losses worldwide. Antimicrobial peptides (AMPs) are amphipathic cationic oligopeptides with which the development of pathogenic microorganisms has been inhibited. Therefore, in this study, we evaluate antimicrobial activity of mesoporous silica nanoparticles (MSN5.4) loaded with human β-defensin-2 (hβD2) and two mutants (TRX-hβD2-M and hβD2-M) against Cmm. hβD2, TRX-hβD2-M and hβD2-M presented a half-maximum inhibitory concentration (IC₅₀) of 3.64, 1.56 and 6.17 μg/mL, respectively. MSNs had average particle sizes of 140 nm (SEM) and a tunable pore diameter of 4.8 up to 5.4 nm (BJH). AMPs were adsorbed more than 99% into MSN and a first release after 24 h was observed. The MSN loaded with the AMPs inhibited the growth of Cmm in solid and liquid media. It was also determined that MSNs protect AMPs from enzymatic degradation when the MSN/AMPs complexes were exposed to a pepsin treatment. An improved AMP performance was registered when it was adsorbed in the mesoporous matrix. The present study could expand the applications of MSNs loaded with AMPs as a biological control and provide new tools for the management of phytopathogenic microorganisms.

Fabrication of Biomolecule-Covalent-Organic-Framework Composites as Responsive Platforms for Smart Regulation of Fermentation Application

Exploration of novel material platforms to protect biological preservatives and realize intelligent regulation during fermentation is of great significance in industry. Herein, we established an intelligent responsive platform by introducing antimicrobial biomolecules (nisin) into rationally designed covalent organic frameworks (COFs), resulting in a new type of "smart formulation", which could responsively inhibit microbial contamination and ensure the orderly progression of the fermentation process. The encapsulated biomolecules retained their activity while exhibiting enhanced stability and pH-responsive releasing process (100% bacteriostatic efficiency at a pH of 3), which can ingeniously adapt to the environmental variation during the fermentation process and smartly fulfill the regulation needs. Moreover, the nisin@COF composites would not affect the fermentation strains. This study will pave a new avenue for the preparation of highly efficient and intelligent antimicrobial agents for the regulation of the fermentation process and play valuable roles in the drive toward green and sustainable biomanufacturing.

Insights into the intraparticle morphology of dendritic mesoporous silica nanoparticles from electron tomographic reconstructions

HYPOTHESIS

Although many synthetic pathways allow to fine-tune the morphology of dendritic mesoporous silica nanoparticles (DMSNs), the control of their particle size and mesopore diameter remains a challenge. Our study focuses on either increasing the mean particle size or adjusting the pore size distribution, changing only one parameter (particle or pore size) at a time. The dependence of key morphological features (porosity; pore shape and pore dimensions) on radial distance from the particle center has been investigated in detail.

EXPERIMENTS

Three-dimensional reconstructions of the particles obtained by scanning transmission electron microscopy (STEM) tomography were adapted as geometrical models for the quantification of intraparticle morphologies by radial porosity and chord length distribution analyses. Structural properties of the different synthesized DMSNs have been complementary characterized using TEM, SEM, nitrogen physisorption, and dynamic light scattering.

FINDINGS

The successful independent tuning of particle and pore sizes of the DMSNs could be confirmed by conventional analysis methods. Unique morphological features, which influence the uptake and release of guest molecules in biomedical applications, were uncovered from analyzing the STEM tomography-based reconstructions. It includes the quantification of structural hierarchy, identification of intrawall openings and pores, as well as the distinction of pore shapes (conical vs. cylindrical).

Pre-formulation and delivery strategies for the development of bacteriocins as next generation antibiotics

Bacteriocins, a class of antimicrobial peptide produced by bacteria, may offer a potential alternative to traditional antibiotics, an important step towards mitigating the ever-increasing antimicrobial resistance crisis. They are active against a range of clinically relevant Gram-positive and Gram-negative bacteria. Bacteriocins have been discussed in the literature for over a century. Although they are used as preservatives in food, no medicine based on their antimicrobial activity exists on the market today. In order to formulate them into clinical antibiotics, pre-formulation studies on their biophysical and physicochemical properties that will influence their activity in vivo and their stability during manufacture must be elucidated. Thermal, pH and enzymatic stability of bacteriocins are commonly studied and regularly reported in the literature. Solubility, permeability and aggregation properties on the other hand are less frequently reported for many bacteriocins, which may contribute to their poor clinical progression. Promising cytotoxicity studies report that bacteriocins exhibit few cytotoxic effects on a variety of mammalian cell lines, at active concentrations. This review highlights the lack of quantitative data and in many cases even qualitative data, on bacteriocins' solubility, stability, aggregation, permeability and cytotoxicity. The formulation strategies that have been explored to date, proposed routes of administration, trends in in vitro/in vivo behaviour and efforts in clinical development are discussed. The future promise of bacteriocins as a new generation of antibiotics may require tailored local delivery strategies to fulfil their potential as a force to combat antimicrobial-resistant bacterial infections.

Tuning the strength and swelling of an injectable polysaccharide hydrogel and the subsequent release of a broad spectrum bacteriocin, nisin A

Bacteriocins, which are antimicrobial peptides, are a potential alternative to current ineffective antimicrobial therapies. They can inhibit the growth of clinically relevant pathogens but their proteinaceous nature renders them susceptible to degradation and deactivation in vivo. We have designed injectable polysaccharide hydrogels for the controlled release of an incorporated bacteriocin, nisin. Nisin was encapsulated into these hydrogels which were composed of varying percentages of oxidised dextran, alginate functionalised with hydrazine groups and glycol chitosan. The nisin gels exhibited antimicrobial activity against Staphylococcus aureus up to 10 days. The incorporation of a deacetylated chitosan and the reduction of alginate-hydrazine could be used to tune the gel's swelling behaviour, strength and the subsequent release profile of nisin. Glycol chitosan also shows synergistic inhibition of S. aureus with nisin.

Membrane Interactions of Virus-like Mesoporous Silica Nanoparticles

In the present study, we investigated lipid membrane interactions of silica nanoparticles as carriers for the antimicrobial peptide LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES). In doing so, smooth mesoporous nanoparticles were compared to virus-like mesoporous nanoparticles, characterized by a "spiky" external surface, as well as to nonporous silica nanoparticles. For this, we employed a combination of neutron reflectometry, ellipsometry, dynamic light scattering, and ζ-potential measurements for studies of bacteria-mimicking bilayers formed by palmitoyloleoylphosphatidylcholine/palmitoyloleoylphosphatidylglycerol. The results show that nanoparticle topography strongly influences membrane binding and destabilization. We found that virus-like particles are able to destabilize such lipid membranes, whereas the corresponding smooth silica nanoparticles are not. This effect of particle spikes becomes further accentuated after loading of such particles with LL-37. Thus, peptide-loaded virus-like nanoparticles displayed more pronounced membrane disruption than either peptide-loaded smooth nanoparticles or free LL-37. The structural basis of this was clarified by neutron reflectometry, demonstrating that the virus-like nanoparticles induce trans-membrane defects and promote incorporation of LL-37 throughout both bilayer leaflets. The relevance of such effects of particle spikes for bacterial membrane rupture was further demonstrated by confocal microscopy and live/dead assays on Escherichia coli bacteria. Taken together, these findings demonstrate that topography influences the interaction of nanoparticles with bacteria-mimicking lipid bilayers, both in the absence and presence of antimicrobial peptides, as well as with bacteria. The results also identify virus-like mesoporous nanoparticles as being of interest in the design of nanoparticles as delivery systems for antimicrobial peptides.

Real-Time Tracking of Highly Luminescent Mesoporous Silica Particles Modified with Europium β-Diketone Chelates in Living Cells

Highly luminescent europium complexes modified mesoporous silica particles (MSP) were synthesized as an imaging probes for both in-vitro diagnostic and in-vivo cellular tracking agents. Europium β-diketone chelates (4,4,4-trifluoro-l-(2-thienyl)-l,3-butanedione) trioctylphosphine europium (III) (Eu(TTA)₃(P(Oct)₃)₃) were incorporated inside the nanocavities that existed in hierarchical MSP (Eu@MSP). The MSP and Eu@MSP on mouse bone marrow-derived macrophages (BMDMs) did not show any toxic effect. The MSP and Eu@MSP in the BMDMs were found at cytoplasm without any degradation and immunogenicity. However, both pro- and anti-inflammatory cytokines of macrophages were significantly increased when lipopolysaccharide and a high concentration (100 μg/mL) of MSP and Eu@MSP were treated simultaneously.

Isolation and identification of novel antibacterial peptides produced by Lactobacillus fermentum SHY10 in Chinese pickles

The aim of this study was to isolate and identify antibacterial peptides (ABPs) produced by lactic acid bacteria (LAB) in Chinese pickles. The cell-free supernatant collected from the culture of LAB with antibacterial activity against Staphylococcus aureus was used to purify ABPs. A total of 14 strains of LAB were found to have antibacterial activity. Among them, Lactobacillus fermentum (L. fermentum) SHY10 exhibited the most effective antibacterial activity. The antibacterial activity of cell-free supernatant reached the highest level after 20 h of L. fermentum SHY10 culture. Three novel ABPs were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In particular, the NQGPLGNAHR peptide showed antibacterial activity with an IC₅₀ value of 0.957 mg/mL. In addition, molecular docking analysis revealed that this peptide interacted with DNA gyrase and dihydrofolate reductase by salt bridge formation, hydrogen bond interactions, and metal contact.

Degradation of silica particles functionalised with essential oil components under simulated physiological conditions

In this work, the biodurability of three silica particle types (synthetic amourphous silica, MCM-41 microparticles, MCM-41 nanoparticles) functionalised with three different essential oil components (carvacrol, eugenol, vanillin) was studied under conditions that represented the human gastrointestinal tract and lysosomal fluid. The effect of particle type, surface immobilised component and mass quantity on the physico-chemical properties of particles and silicon dissolution was determined. Exposure to biological fluids did not bring about changes in the zeta potential values or particle size distribution of the bare or functionalised materials, but the in vitro digestion process partially degraded the structure of the MCM-41 nanoparticles. Functionalisation preserved the structure of the MCM-41 nanoparticles after simulating an in vitro digestion process, and significantly decreased the amount of silicon dissolved after exposing different particles to both physiological conditions, independently of the essential oil component anchored to their surface. The MCM-41 microparticles showed the highest solubility, while synthetic amorphous silica presented the lowest levels of dissolved silicon. The study of these modified silica particles under physiological conditions could help to predict the toxicological behaviour of these new materials.

Formulation technologies and advances for oral delivery of novel nitroimidazoles and antimicrobial peptides

Antibiotic resistance has become a global crisis, driving the exploration for novel antibiotics and novel treatment approaches. Among these research efforts two classes of antibiotics, bicyclic nitroimidazoles and antimicrobial peptides, have recently shown promise as novel antimicrobial agents with the possibility to treat multi-drug resistant infections. However, they suffer from the issue of poor oral bioavailability due to disparate factors: low solubility in the case of nitroimidazoles (BCS class II drugs), and low permeability in the case of peptides (BCS class III drugs). Moreover, antimicrobial peptides present another challenge as they are susceptible to chemical and enzymatic degradation, which can present an additional pharmacokinetic hurdle for their oral bioavailability. Formulation technologies offer a potential means for improving the oral bioavailability of poorly permeable and poorly soluble drugs, but there are still drawbacks and limitations associated with this approach. This review discusses in depth the challenges associated with oral delivery of nitroimidazoles and antimicrobial peptides and the formulation technologies that have been used to overcome these problems, including an assessment of the drawbacks and limitations associated with the technologies that have been applied. Furthermore, the potential for supercritical fluid technology to overcome the shortcomings associated with conventional drug formulation methods is reviewed.

Antimicrobials for food and feed; a bacteriocin perspective

Bacteriocins are natural antimicrobials that have been consumed via fermented foods for millennia and have been the focus of renewed efforts to identify novel bacteriocins, and their producing microorganisms, for use as food biopreservatives and other applications. Bioengineering bacteriocins or combining bacteriocins with multiple modes of action (hurdle approach) can enhance their preservative effect and reduces the incidence of antimicrobial resistance. In addition to their role as food biopreservatives, bacteriocins are gaining credibility as health modulators, due to their ability to regulate the gut microbiota, which is strongly associated with human wellbeing. Indeed the strengthening link between the gut microbiota and obesity make bacteriocins ideal alternatives to Animal Growth Promoters (AGP) in animal feed also. Here we review recent advances in bacteriocin research that will contribute to the development of functional foods and feeds as a consequence of roles in food biopreservation and human/animal health.

Complexation between antimicrobial peptides and polyelectrolytes

As a result of increasing bacterial resistance against antibiotics, we are facing an emerging health crisis, in which 'simple' infections may no longer be treatable. One class of molecules attracting interest in this context is antimicrobial peptides (AMPs), and considerable research efforts have been directed to identifying selective and potent AMPs. In addition, since in vivo delivery of AMPs is challenging, there is an emerging awareness that successful development of AMP therapeutics can be facilitated by careful design of AMPs delivery systems. In the present overview, we discuss polyelectrolyte complexation as a strategy to deliver AMPs. In doing so, key factors for AMP-polyelectrolyte complexation are illustrated for AMP-polyelectrolyte nanoparticle formation, as well as for AMP incorporation in polyelectrolyte microgels and multilayer structures, and consequences of these for functional performance exemplified.

Protecting bactofencin A to enable its antimicrobial activity using mesoporous matrices

There is huge global concern surrounding the emergence of antimicrobial resistant bacteria and this is resulting in an inability to treat infectious diseases. This is due to a lack of new antimicrobials coming to the market and irresponsible use of traditional antibiotics. Bactofencin A, a novel antimicrobial peptide which shows potential as an antibiotic, is susceptible to enzyme degradation. To improve its solution stability and inherent activity, bactofencin A was loaded onto a traditional silica mesoporous matrix, SBA-15, and a periodic mesoporous organosilane, MSE. The loading of bactofencin A was considerably higher onto SBA-15 than MSE due to the hydrophilic nature of SBA-15. While there was no detectable peptide released from SBA-15 into phosphate buffered saline and only 20% of the peptide loaded onto MSE was released, the loaded matrices showed enhanced activity compared to the free peptide during in vitro antimicrobial assays. In addition, the mesoporous matrices were found to protect bactofencin A against enzymatic degradation where results showed that the SBA-15 and MSE with loaded bactofencin A exposed to trypsin inhibited the growth of S. aureus while a large decrease in activity was observed for free bactofencin upon exposure to trypsin. Thus, the activity and stability of bactofencin A can be enhanced using mesoporous matrices and these matrices may enable its potential development as a novel antibiotic. This work also shows that in silico studies looking at surface functional group and size complementarity between the peptide and the protective matrix could enable the systemic selection of a mesoporous matrix for individual bacteriocins with potential antimicrobial therapeutic properties.