Induced resistance to the antimicrobial peptide lactoferricin B inStaphylococcus aureus

Analyzing resistome in soil and Human gut: a study on the characterization and risk evaluation of antimicrobial peptide resistance

Objective

The limited existing knowledge regarding resistance to antimicrobial peptides (AMPs) is hindering their broad utilization. The aim of this study is to enhance the understanding of AMP resistance, a pivotal factor in the exploration of alternative drug development in response to the escalating challenge of antibiotic resistance.

Methods

We utilized metagenomic functional selection to analyze genes resistant to AMPs, with a specific focus on the microbiota in soil and the human gut. Through a combination of experimental methods and bioinformatics analyses, our investigation delved into the possibilities of the evolution of resistance to AMPs, as well as the transfer or interchange of resistance genes among the environment, the human body, and pathogens. Additionally, we examined the cross-resistance between AMPs and evaluated interactions among AMPs and conventional antibiotics.

Results

The presence of AMP resistance, including various resistance mechanisms, was observed in both soil and the human gut microbiota, as indicated by our findings. Significantly, the study underscored the facile evolution of AMP resistance and the potential for gene sharing or exchange among different environments. Notably, cross-resistance among AMPs was identified as a phenomenon, while cross-resistance between AMPs and antibiotics was found to be relatively infrequent.

Conclusion

The results of our study highlight the significance of taking a cautious stance when considering the extensive application of AMPs. It is imperative to thoroughly assess potential resistance risks, with a particular focus on the development of resistance to AMPs across diverse domains. A comprehensive grasp of these aspects is essential for making well-informed decisions and ensuring the responsible utilization of AMPs in the ongoing fight against antibiotic resistance.

The Remarkable Innate Resistance of Burkholderia bacteria to Cationic Antimicrobial Peptides: Insights into the Mechanism of AMP Resistance

Gram-negative bacteria belonging to the genus Burkholderia are remarkably resistant to broad-spectrum, cationic, antimicrobial peptides (AMPs). It has been proposed that this innate resistance is related to changes in the outer membrane lipopolysaccharide (OM LPS), including the constitutive, essential modification of outer membrane Lipid A phosphate groups with cationic 4-amino-4-deoxy-arabinose. This modification reduces the overall negative charge on the OM LPS which may change the OM structure and reduce the binding, accumulation, and permeation of cationic AMPs. Similarly, the Gram-negative pathogen Pseudomonas aeruginosa can quickly become resistant to many AMPs by multiple mechanisms, frequently, including activation of the arn operon, which leads, transiently, to the same modification of Lipid A. We recently discovered a set of synthetically evolved AMPs that do not invoke any resistance in P. aeruginosa over multiple passages and thus are apparently not inhibited by aminorabinosylation of Lipid A in P. aeruginosa. Here we test these resistance-avoiding peptides, within a set of 18 potent AMPs, against Burkholderia thailandensis. We find that none of the AMPs tested have measurable activity against B. thailandensis. Some were inactive at concentrations as high as 150 μM, despite all having sterilizing activity at ≤ 10 μM against a panel of common, human bacterial pathogens, including P. aeruginosa. We speculate that the constitutive modification of Lipid A in members of the Burkholderia genus is only part of a broader set of modifications that change the architecture of the OM to provide such remarkable levels of resistance to cationic AMPs.

Bactericidal activities and Action mechanism of the Novel Antimicrobial Peptide Hylin a1 and its analog peptides against Acinetobacter baumannii infection

We developed an antimicrobial peptide (AMP) as a candidate substance for replacing antibiotics. Previously, a novel 18-amino acid antimicrobial peptide Hylin a1 was isolated from an electro-stimulated arboreal South American frog Hypsiboas albopunctatus, and was found to demonstrate antimicrobial activity and cytotoxicity. In a recent study, the analog peptides were designed based on the parent peptide Hylin a1 to decrease toxicity and to maintain antimicrobial efficacy. The analog peptides were substituted with alanine and lysine, resulting in the formation of amphipathic α-helical structures in membrane-mimicking environments and in the induction of hydrophobic moments and net charges. Moreover, the analog peptides showed lower hemolytic effects and mammalian cell selectivity than Hylin a1. In particularly Hylin a1-11K and Hylin a1-15K exhibited broad-spectrum antimicrobial activity and anti-biofilm activity against carbapenem-resistant Acinetobacter baumannii. Permeability assays indicated that analog peptides eliminated bacteria by binding to lipopolysaccharide and by disrupting the bacterial membrane. Hylin a1-11K and Hylin a1-15K reduced inflammation by suppressing pro-inflammatory cytokines expression by A. baumannii infection and effectively ameliorated carbapenem-resistant A. baumannii infection in mice. Therefore, our results suggest that the analog peptide substituted with several residues based on Hylin a1 have antibacterial and anti-inflammatory activity, and may be effective in the treatment of carbapenem-resistant A. baumannii infection.

Revealing AMP mechanisms of action through resistance evolution and quantitative proteomics

Antimicrobial resistance (AMR) is a significant public health issue that threatens our ability to treat common infections. AMR often emerges in bacteria through upregulation of proteins that allow a subpopulation of resistant bacteria to proliferate through natural selection. Identifying these proteins is crucial for understanding how AMR develops in bacteria and is essential in developing novel therapeutics to combat the threat of widespread AMR. Mass spectrometry-based proteomics is a powerful tool for understanding the biochemical pathways of biological systems, lending remarkable insight into AMR mechanisms in bacteria through measuring the changing protein abundances as a result of antibiotic treatment. Here, we describe a serial passaging method for evolving resistance in bacteria that implements quantitative proteomics to reveal the differential proteomes of resistant bacteria. The focus herein is on antimicrobial peptides (AMPs), but the approach can be generalized for any antimicrobial compound. Comparative proteomics of sensitive vs. resistance strains in response to AMP treatment reveals mechanisms to survive the bioactive compound and points to the mechanism of action for novel AMPs.

Resistance Mechanisms to Antimicrobial Peptides in Gram-Positive Bacteria

With the alarming increase of infections caused by pathogenic multidrug-resistant bacteria over the last decades, antimicrobial peptides (AMPs) have been investigated as a potential treatment for those infections, directly through their lytic effect or indirectly, due to their ability to modulate the immune system. There are still concerns regarding the use of such molecules in the treatment of infections, such as cell toxicity and host factors that lead to peptide inhibition. To overcome these limitations, different approaches like peptide modification to reduce toxicity and peptide combinations to improve therapeutic efficacy are being tested. Human defense peptides consist of an important part of the innate immune system, against a myriad of potential aggressors, which have in turn developed different ways to overcome the AMPs microbicidal activities. Since the antimicrobial activity of AMPs vary between Gram-positive and Gram-negative species, so do the bacterial resistance arsenal. This review discusses the mechanisms exploited by Gram-positive bacteria to circumvent killing by antimicrobial peptides. Specifically, the most clinically relevant genera, Streptococcus spp., Staphylococcus spp., Enterococcus spp. and Gram-positive bacilli, have been explored.

Antifungal Activity of Antimicrobial Peptides and Proteins against Aspergillus fumigatus

Antimicrobial peptides and proteins (AMPs) provide an important line of defence against invading microorganisms. However, the activity of AMPs against the human fungal pathogen Aspergillus fumigatus remains poorly understood. Therefore, the aim of this study was to characterise the anti-Aspergillus activity of specific human AMPs, and to determine whether A. fumigatus can possess resistance to specific AMPs, as a result of in-host adaptation. AMPs were tested against a wide range of clinical isolates of various origins (including cystic fibrosis patients, as well as patients with chronic and acute aspergillosis). We also tested a series of isogenic A. fumigatus isolates obtained from a single patient over a period of 2 years. A range of environmental isolates, obtained from soil in Scotland, was also included. Firstly, the activity of specific peptides was assessed against hyphae using a measure of fungal metabolic activity. Secondly, the activity of specific peptides was assessed against germinating conidia, using imaging flow cytometry as a measure of hyphal growth. We showed that lysozyme and histones inhibited hyphal metabolic activity in all the A. fumigatus isolates tested in a dose-dependent fashion. In addition, imaging flow cytometry revealed that histones, β-defensin-1 and lactoferrin inhibited the germination of A. fumigatus conidia.

Systemic Administration of Avian Defensin 7: Distribution, Cellular Target, and Antibacterial Potential in Mice

Defensins are natural antimicrobial peptides. The avian beta-defensin AvBD7 isolated from the chicken bone marrow possess broad antibacterial spectrum and strong resistance to proteolysis. However, its ability to fight systemic infections of major concern for public health, such as salmonellosis, is unknown. As a first approach, fluorescence labeling of AvBD7 allowed to track its systemic distribution after intraperitoneal injection in mice using whole body live imaging. It was associated to peritoneal cells and to deeper organs such as the liver. In the next step, the use of labeled AvBD7 allowed to observe its interaction with murine macrophages in culture. After incubation, it was able to penetrate inside the cells through an endocytosis-like mechanism. Furthermore, natural AvBD7 contributed to the control of intracellular multiplication of a multidrug resistant Salmonella strain, after incubation with infected macrophages. Finally, administration in a model of systemic lethal Salmonella infection in mice led to significant improvement of mouse survival, consistently with significant reduction of the liver bacterial load. In conclusion, the results reveal a hitherto unknown intracellular antibacterial effect of AvBD7 in Salmonella target cells and support AvBD7 as a candidate of interest for the treatment of infectious diseases caused by multidrug-resistant pathogenic Enterobacteriaceae.

Regulation of antimicrobial resistance by extracytoplasmic function (ECF) sigma factors

Extracytoplasmic function (ECF) sigma factors are a subfamily of σ⁷⁰ sigma factors that activate genes involved in stress-response functions. In many bacteria, ECF sigma factors regulate resistance to antimicrobial compounds. This review will summarize the ECF sigma factors that regulate antimicrobial resistance in model organisms and clinically relevant pathogens.

Defensive remodeling: How bacterial surface properties and biofilm formation promote resistance to antimicrobial peptides

Multidrug resistance bacteria are a major concern worldwide. These pathogens cannot be treated with conventional antibiotics and thus alternative therapeutic agents are needed. Antimicrobial peptides (AMPs) are considered to be good candidates for this purpose. Most AMPs are short and positively charged amphipathic peptides, which are found in all known forms of life. AMPs are known to kill bacteria by binding to the negatively charged bacterial surface, and in most cases cause membrane disruption. Resistance toward AMPs can be developed, by modification of bacterial surface molecules, secretion of protective material and up-regulation or elimination of specific proteins. Because of the general mechanisms of attachment and action of AMPs, bacterial resistance to AMPs often involves biophysical and biochemical changes such as surface rigidity, cell wall thickness, surface charge, as well as membrane and cell wall modification. Here we focus on the biophysical, surface and surrounding changes that bacteria undergo in acquiring resistance to AMPs. In addition we discuss the question of whether bacterial resistance to administered AMPs might compromise our innate immunity to endogenous AMPs. This article is part of a Special Issue entitled: Bacterial Resistance to Antimicrobial Peptides.

Synthetic biology of antimicrobial discovery

Antibiotic discovery has a storied history. From the discovery of penicillin by Sir Alexander Fleming to the relentless quest for antibiotics by Selman Waksman, the stories have become like folklore used to inspire future generations of scientists. However, recent discovery pipelines have run dry at a time when multidrug-resistant pathogens are on the rise. Nature has proven to be a valuable reservoir of antimicrobial agents, which are primarily produced by modularized biochemical pathways. Such modularization is well suited to remodeling by an interdisciplinary approach that spans science and engineering. Herein, we discuss the biological engineering of small molecules, peptides, and non-traditional antimicrobials and provide an overview of the growing applicability of synthetic biology to antimicrobials discovery.

Differential adaptive responses of Staphylococcus aureus to in vitro selection with different antimicrobial peptides

We subjected Staphylococcus aureus ATCC 29213 to serial passage in the presence of subinhibitory concentrations of magainin 2 and gramicidin D for several hundred generations. We obtained S. aureus strains with induced resistance to magainin 2 (strain 55MG) and gramicidin D (strain 55GR) that showed different phenotypic changes in membrane properties. Both exhibited a change in membrane phospholipid content and an increase in membrane rigidity, while an alteration in net charge compared to that of the control occurred only in the case of 55MG.

Identification of cell-penetrating peptides that are bactericidal to Neisseria meningitidis and prevent inflammatory responses upon infection

Meningococcal disease is characterized by a fast progression and a high mortality rate. Cell-penetrating peptides (CPPs), developed as vectors for cargo delivery into eukaryotic cells, share structural features with antimicrobial peptides. A screen identified two CPPs, transportan-10 (TP10) and model amphipathic peptide (MAP), with bactericidal action against Neisseria meningitidis. Both peptides were active in human whole blood at micromolar concentrations, while hemolysis remained negligible. Additionally, TP10 exhibited significant antibacterial activity in vivo. Uptake of SYTOX green into live meningococci was observed within minutes after TP10 treatment, suggesting that TP10 may act by membrane permeabilization. Apart from its bactericidal activity, TP10 suppressed inflammatory cytokine release from macrophages infected with N. meningitidis as well as from macrophages stimulated with enterobacterial and meningococcal lipopolysaccharide (LPS). Finally, incubation with TP10 reduced the binding of LPS to macrophages. This novel endotoxin-inhibiting property of TP10, together with its antimicrobial activity in vivo, indicates the possibility to design peptide-based therapies for infectious diseases.

In vitro evaluation of the potential for resistance development to ceragenin CSA-13

OBJECTIVES

Though most bacteria remain susceptible to endogenous antimicrobial peptides, specific resistance mechanisms are known. As mimics of antimicrobial peptides, ceragenins were expected to retain antibacterial activity against Gram-positive and -negative bacteria, even after prolonged exposure. Serial passaging of bacteria to a lead ceragenin, CSA-13, was performed with representative pathogenic bacteria. Ciprofloxacin, vancomycin and colistin were used as comparators. The mechanisms of resistance in Gram-negative bacteria were elucidated.

METHODS

Susceptible strains of Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii were serially exposed to CSA-13 and comparators for 30 passages. MIC values were monitored. Alterations in the Gram-negative bacterial membrane composition were characterized via mass spectrometry and the susceptibility of antimicrobial-peptide-resistant mutants to CSA-13 was evaluated.

RESULTS

S. aureus became highly resistant to ciprofloxacin after <20 passages. After 30 passages, the MIC values of vancomycin and CSA-13 for S. aureus increased 9- and 3-fold, respectively. The Gram-negative organisms became highly resistant to ciprofloxacin after <20 passages. MIC values of colistin for P. aeruginosa and A. baumannii increased to ≥100 mg/L after 20 passages. MIC values of CSA-13 increased to ∼20-30 mg/L and plateaued over the course of the experiment. Bacteria resistant to CSA-13 displayed lipid A modifications that are found in organisms resistant to antimicrobial peptides.

CONCLUSIONS

CSA-13 retained potent antibacterial activity against S. aureus over the course of 30 serial passages. Resistance generated in Gram-negative bacteria correlates with modifications to the outer membranes of these organisms and was not stable outside of the presence of the antimicrobial.

Effect of cholesterol on the membrane interaction of Modelin-5 isoforms

Modelin-5 isoforms were used to gain an insight into the effects of amidation on antimicrobial selectivity. When tested against Escherichia coli, amidation increased toxicity 10-fold (MIC = 31.25 μM) while showing limited increased hemolytic activity (2% lysis). Our results show that both the amidated and non-amidated peptides had a disordered structure in aqueous solution (<18% helical) and folded to form helices at the membrane interface (for example, >43% in the presence of DMPC). The stabilization of the helical structure by amidation has previously been shown to play a key role in increasing antibacterial efficacy. The presence of cholesterol in the membrane increases the packing density (C(s)(-1) values 25-33 mN m(-1)) and so prevents the peptide from forming stable association with the membrane, which is evidenced by the higher binding coefficient (K(d)) in the presence of cholesterol: 57.70 μM for Modelin-5-COOH and 35.64 μM for Modelin-5-CONH(2) compared to the presence of E. coli lipid extract (10 μM), which would prevent local concentration of the peptide at the bilayer interface as seen by reduction in monolayer interaction. This in turn would be predicted to inhibit activity.

Egg yolk phosvitin and functional phosphopeptides--review

Phosphopeptides are among the most interesting biomolecules with characteristic molecular structure and functions. They usually contain clusters of phosphoserines, which can effectively bind calcium and iron, and inhibit formation of insoluble calcium phosphates or iron complexes. Therefore, phosphopeptides can increase calcium or iron bioavailability and prevent lipid oxidation in foods. Milk protein casein has been currently used by industry to produce phosphopeptides. Egg yolk phosvitin is considered as the most phosphorylated protein found in the nature. Phosvitin from egg yolk can be much better source for producing phosphopeptides with varying sizes and functions than casein because it contains much greater number of phosphates in the molecule than casein. However, still phosvitin has not been subjected to considerable attention with regard to bioactive peptides production.

Cloning and expression of antibacterial goat lactoferricin from Escherichia coli AD494(DE3)pLysS expression system

Goat lactoferricin (GLfcin), an antibacterial peptide, is released from the N terminus of goat lactoferrin by pepsin digestion. Two GLfcin-related cDNAs, GLfcin L and GLfcin S, encoding Ala20-Ser60 and Ser36-Ser60 of goat lactoferrin, respectively, were cloned into the pET-23a(+) expression vector upstream from (His)6-Tag gene and transformed into Escherichia coli AD494(DE3)pLysS expression host. After being induced by isopropyl-beta-D-thiogalactopyranoside (IPTG), two (His)6-Tag fused recombinant lactoferricins, GLfcin L-His*Tag and GLfcin S-His*Tag, were expressed in soluble form within the E. coli cytoplasm. The GLfcin L-His*Tag and GLfcin S-His*Tag were purified using HisTrap affinity chromatography. According to an antibacterial activity assay using the agar diffusion method, GLfcin L-His*Tag had antibacterial activity against E. coli BCRC 11549, Staphylococcus aureus BCRC 25923, and Propionibacterium acnes BCRC 10723, while GLfcin S-His*Tag was able to inhibit the growth of E. coli BCRC 11549 and P. acnes BCRC 10723. These two recombinant lactoferricins behaved as thermostable peptides, which could retain their activity for up to 30 min of exposure at 100 degrees C.

Zwitterionic phospholipids and sterols modulate antimicrobial peptide-induced membrane destabilization

Cationic amphipathic alpha-helical peptides preferentially disrupt anionic lipids in mixed model membranes, potentially causing a catastrophic release of the cell contents or attenuation of the membrane potential. The effective role of such peptides requires considerable discrimination between target and host cells, which is likely to occur at the level of the cell membrane. Here, we explore the roles of a variety of common membrane constituents in mediating the interaction between the antimicrobial peptide pleurocidin and model membranes. We employ intrinsic tryptophan fluorescence and circular dichroism to observe the effect of increasing concentrations of sterol in the membrane on peptide binding, using (2)H solid-state NMR of chain deuterated lipids simultaneously to probe the effective chain disruption of the anionic phospholipid component of the membrane. We show that the degree of ordering of the lipid acyl chains in the membrane is dependent on the nature of the zwitterionic phospholipid headgroup in mixed anionic membranes. Furthermore, the presence of cholesterol and ergosterol increases acyl chain order in the liquid crystalline model membranes, but to differing degrees. Our results show how sterols can protect even negatively charged membranes from the disruptive effects of antimicrobial peptides, thereby providing a molecular view of the differences in sensitivity of various target membranes to linear cationic antibiotic peptides where bacteria (no sterols) are most susceptible, lower eukaryotes including fungi (containing ergosterol) exhibit an intermediate degree of sensitivity, and higher organisms (containing cholesterol) are largely resistant to antimicrobial peptides.

Antimicrobial and host-defense peptides as new anti-infective therapeutic strategies

Short cationic amphiphilic peptides with antimicrobial and/or immunomodulatory activities are present in virtually every life form, as an important component of (innate) immune defenses. These host-defense peptides provide a template for two separate classes of antimicrobial drugs. Direct-acting antimicrobial host-defense peptides can be rapid-acting and potent, and possess an unusually broad spectrum of activity; consequently, they have prospects as new antibiotics, although clinical trials to date have shown efficacy only as topical agents. But for these compounds to fulfill their therapeutic promise and overcome clinical setbacks, further work is needed to understand their mechanisms of action and reduce the potential for unwanted toxicity, to make them more resistant to protease degradation and improve serum half-life, as well as to devise means of manufacturing them on a large scale in a consistent and cost-effective manner. In contrast, the role of cationic host-defense peptides in modulating the innate immune response and boosting infection-resolving immunity while dampening potentially harmful pro-inflammatory (septic) responses gives these peptides the potential to become an entirely new therapeutic approach against bacterial infections.

LL-37, the only human member of the cathelicidin family of antimicrobial peptides

Antimicrobial peptides and their precursor molecules form a central part of human and mammalian innate immunity. The underlying genes have been thoroughly investigated and compared for a considerable number of species, allowing for phylogenetic characterization. On the phenotypical side, an ever-increasing number of very varied and distinctive influences of antimicrobial peptides on the innate immune system are reported. The basic biophysical understanding of mammalian antimicrobial peptides, however, is still very limited. This is especially unsatisfactory since knowledge of structural properties will greatly help in the understanding of their immunomodulatory functions. The focus of this review article will be on LL-37, the only cathelicidin-derived antimicrobial peptide found in humans. LL-37 is a 37-residue, amphipathic, helical peptide found throughout the body and has been shown to exhibit a broad spectrum of antimicrobial activity. It is expressed in epithelial cells of the testis, skin, the gastrointestinal tract, and the respiratory tract, and in leukocytes such as monocytes, neutrophils, T cells, NK cells, and B cells. It has been found to have additional defensive roles such as regulating the inflammatory response and chemo-attracting cells of the adaptive immune system to wound or infection sites, binding and neutralizing LPS, and promoting re-epthelialization and wound closure. The article aims to report the known biophysical facts, with an emphasis on structural evidence, and to set them into relation with insights gained on phylogenetically related antimicrobial peptides in other species. The multitude of immuno-functional roles is only outlined. We believe that this review will aid the future work on the biophysical, biochemical and immunological investigations of this highly intriguing molecule.

Staphylococcus aureus small colony variants are resistant to the antimicrobial peptide lactoferricin B

OBJECTIVES

To determine whether Staphylococcus aureus small colony variants (SCVs) are resistant to the antimicrobial peptide lactoferricin B. To assess if deficiency in transmembrane potential, a common characteristic of SCVs that are haemin- or menadione-auxotrophs, affects the uptake of the peptide into the bacterial cytoplasm.

METHODS

A broth microdilution technique was used for susceptibility testing to determine the MIC of lactoferricin B for SCVs with three different auxotrophisms (haemin, menadione or thymidine) and their isogenic parent strains. Both clinical isolates and genetically defined mutants were used. The internalization of lactoferricin B in a hemB mutant and the respective parent strain was studied using transmission electron microscopy and immunogold labelling.

RESULTS

All SCVs showed reduced susceptibility to lactoferricin B irrespective of their auxotrophy compared with their isogenic parent strains. The MIC for all SCVs was >256 mg/L, whereas the MICs for the parent strains ranged from 16-256 mg/L. Surprisingly, the hemB mutant contained significantly more lactoferricin B intracellularly than the respective parent strain.

CONCLUSIONS

The resistance mechanism of SCVs towards the antimicrobial peptide lactoferricin B is presumably caused by the metabolic changes present in SCVs rather than by a changed transmembrane potential of SCVs or reduced uptake of the peptide.