Unravelling the mechanism of action of “de novo” designed peptide P1 with model membranes and gram-positive and gram-negative bacteria

Interaction of selected alkoxy naringenin oximes with model and bacterial membranes

Naringenin is a flavonoid found in many fruits and herbs, most notably in grapefruits. In recent years, this compound and its derivatives have been of great interest due to their high biological activity, including fungicidal and bactericidal effects, also in relation to multidrug-resistant bacteria. Membrane interactions of naringenin oxime (NO) and its 7-O-alkyl (7-alkoxy) derivatives, such as methyl (7MENO), ethyl (7ETNO), isopropyl (7IPNO), n-butyl (7BUNO) and n-pentyl (7PENO) were studied. Thermotropic properties of model membranes were investigated via differential scanning calorimetry (DSC), the influence on lipid raft mimicking giant unilamellar vesicles (GUVs) via fluorescence microscopy, and membrane permeability via measuring calcein leakage from liposomes. Molecular calculations supplemented the study. The influence of naringenin oximes on two strains of multidrug resistant bacteria: Staphylococcus aureus KJ and Enterococcus faecalis 37VRE was also investigated. In DSC studies all compounds reduced the temperature and enthalpy of main phase transition and caused disappearing of the pretransition. NO was the least active. The reduction in the area of surface domains in GUVs was observed for NO. Compounds NO and 7BUNO resulted in very low secretion of calcein from liposomes (permeability < 3 %). The highest results were observed for 7MENO (88.4 %) and 7IPNO (78.5 %). When bacterial membrane permeability was investigated all compounds caused significant release of propidium iodide from S. aureus (31.6-87.0 % for concentration 128 μg/mL). In the case of E. faecalis, 7ETNO (75.7 %) and NO (28.8 %) were the most active. The rest of the tested compounds showed less activity (permeability < 13.9 %). The strong evidence was observed that antibacterial activity of the tested compounds may be associated with their interaction with bacterial membrane.

In-vitro antimicrobial activity of AF-DP protein and in-silico approach of cell membrane disruption

Microbial resistance against common antibiotics has become one of the most serious threats to human health. The increasing statistics on this problem show the necessity of finding a way to deal with it. In recent years, antimicrobial peptides with unique properties and the capability of targeting a wide range of pathogens, have been considered as a potential for replacing common antibiotics. A small chitin-binding protein with anticandidal activity was isolated from Moringa oleifera seeds by Neto and colleagues in 2017, which very much resembled antimicrobial peptides. In this study, the antimicrobial protein 'AF-DP' was identified and characterized. AF-DP was heterologously expressed, purified, and characterized, and its 3D structure was predicted. Six molecular dynamic simulations were performed to investigate how the protein interacts with Gram-negative inner and outer, Gram-positive, fungal, cancerous, and normal mammalian membranes. Also, its antimicrobial and anticancer activity was assessed in vitro via minimum inhibition concentration (MIC) and MTT assays, respectively. This protein with 111 amino acids and a total net charge (of 10.5) has been predicted to be mainly composed of alpha helix and random coils. Its MIC affecting the growth of Escherichia coli, Staphylococcus aureus, and Candida albicans was 30 µg/ml, 100 µg/ml, and 100 µg/ml, respectively; AF-DP showed anticancer activity against MCF-7 breast cancer cell line. Scanning electron microscopic analysis confirmed the creation of pores and scratches on the surface of the bacterial membrane. The results of this research show that AF-DP can be a candidate for the production of new drugs as an AMP with antimicrobial activity.Communicated by Ramaswamy H. Sarma.

Green One-Step Synthesis of Silver Nanoparticles Obtained from Schinus areira Leaf Extract: Characterization and Antibacterial Mechanism Analysis

The increased emergence of antibiotic-resistant bacteria is a serious health problem worldwide. In this sense, silver nanoparticles (AgNPs) have received increasing attention for their antimicrobial activity. In this context, the goal of this study was to produce AgNPs by a green synthesis protocol using an aqueous leaf extract of Schinus areira as biocomposite to later characterize their antimicrobial action. The nanomaterials obtained were characterized by UV‒vis spectroscopy, DLS, TEM, and Raman, confirming the presence of quasi-spherical AgNPs with a negative surface charge and diameter around 11 nm. Afterward, the minimum inhibitory and bactericidal concentration of the AgNPs against Staphylococcus aureus and Escherichia coli were obtained, showing high antibacterial activity. In both of the examined bacteria, the AgNPs were able to raise intracellular ROS levels. In E. coli, the AgNPs can harm the bacterial membrane as well. Overall, it can be concluded that it was possible to obtain AgNPs with colloidal stability and antibacterial activity against Gram-positive and Gram-negative bacteria. Our findings point to at least two separate mechanisms that can cause cell death, one of which involves bacterial membrane damage and the other of which involves intracellular ROS induction.

Innovative Biomedical and Technological Strategies for the Control of Bacterial Growth and Infections

Antibiotics comprise one of the most successful groups of pharmaceutical products. Still, they have been associated with developing bacterial resistance, which has become one of the most severe problems threatening human health today. This context has prompted the development of new antibiotics or co-treatments using innovative tools to reverse the resistance context, combat infections, and offer promising antibacterial therapy. For the development of new alternatives, strategies, and/or antibiotics for controlling bacterial growth, it is necessary to know the target bacteria, their classification, morphological characteristics, the antibiotics currently used for therapies, and their respective mechanisms of action. In this regard, genomics, through the sequencing of bacterial genomes, has generated information on diverse genetic resources, aiding in the discovery of new molecules or antibiotic compounds. Nanotechnology has been applied to propose new antimicrobials, revitalize existing drug options, and use strategic encapsulating agents with their biochemical characteristics, making them more effective against various bacteria. Advanced knowledge in bacterial sequencing contributes to the construction of databases, resulting in advances in bioinformatics and the development of new antimicrobials. Moreover, it enables in silico antimicrobial susceptibility testing without the need to cultivate the pathogen, reducing costs and time. This review presents new antibiotics and biomedical and technological innovations studied in recent years to develop or improve natural or synthetic antimicrobial agents to reduce bacterial growth, promote well-being, and benefit users.

Anti-Candida Potential of Peptides from Immature and Ripe Fruits of Capsicum chinense Jacq

The objective of this work was to purify and evaluate the antifungal potential of peptides present in immature and ripe fruits of Capsicum chinense Jacq. (accession UENF 1706) on the medical importance yeasts. Initially the proteins of these seedless fruits were extracted, precipitated with ammonium sulfate at 70% saturation, followed by heating at 80 °C. Subsequently, the peptide-rich extract was fractionated by DEAE-Sepharose anion exchange. The whole process was monitored by tricine-SDS-PAGE. The results revealed that the fraction retained in anion exchange column, called D2, of immature and ripe fruits significantly inhibit the growth of Candida albicans and C. tropicalis yeasts. Due to the higher yield, the D2 fraction of immature fruits was selected for further purification by reverse phase chromatography on HPLC, where sixteen different fractions (H1-H16) were obtained and these were subjected to antifungal assay at 50 µg mL-1. Although almost all fractions tested had significant growth inhibition, the HI9 fraction inhibit 99% of the two yeasts tested. The effect of treatment with HI3, HI8, HI9, and HI14 fractions on the viability of yeast cells was analyzed due to their strong growth inhibition. We observed that only 50 μg mL-1 of the HI9 fraction is the lethal dose for 100% of the cells of C. albicans and C. tropicalis in the original assay. Although the HI9 fraction had a fungicidal effect on both tested yeasts, we only observed membrane permeabilization for C. tropicalis cells treated with 50 µg mL-1 of this fraction. Through mass spectrometry, we identified that the 6 kDa peptide band of HI9 fraction showed similarity with antimicrobial peptides belonging to the plant defensin family.

1,8-Cineol (Eucalyptol) Disrupts Membrane Integrity and Induces Oxidative Stress in Methicillin-Resistant Staphylococcus aureus

Due to the increased emergence of drug-resistant bacteria, the declining efficiency of traditional antimicrobials has generated severe concerns in recent years. Subsequently, more interest in other antimicrobial agents from natural resources draws more attention as an alternative to conventional medications. This study investigated the bactericidal mechanism of monoterpene 1,8-cineol (eucalyptol), a major compound of various essential oils, against methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial activity of 1,8-cineol was assessed by an MTT assay against clinical and reference MRSA strains. A cell membrane integrity test, followed by zeta potential (ZP) measurements, was performed to evaluate the disruption of the bacterial membrane integrity. Additionally, the cytotoxic effect of this molecule on MRSA bacteria was investigated by monitoring reactive oxygen species (ROS) generation, lipid peroxidation (MDA), and antioxidant enzyme activities (CAT and SOD). Regarding the anti-staphylococcal effect, the obtained results revealed the antibacterial efficacy of 1,8-cineol wherein the minimum inhibitory concentrations were equal to 7.23 mg/mL. Furthermore, it enhanced membrane permeability, with a 5.36-fold increase in nucleic acid and protein leakage as compared with untreated strains, along with the alteration of surface charge (ZP) in MRSA cells. The tested compound caused an increase in ROS generation reaching 17,462 FU and MDA production, reaching 9.56 μM/mg protein, in treated bacterial cells, along with a decrease in oxidative stress enzymes activities. Our findings suggest that 1,8-cineol has the ability to damage the membrane integrity and induce ROS-mediated oxidative stress in MRSA cells, leading to its antagonistic effect against this pathogen and consequently aiding in the reversal of antibiotic resistance.

Antimicrobial properties of the essential oil of Schinus areira (Aguaribay) against planktonic cells and biofilms of S. aureus

The essential oil (EO) of Schinus areira L. (Anacardiaceae) leaves has shown antibacterial activity against Staphylococcus aureus. In this study we aimed to unravel the mechanisms of its antibacterial action by using bacterial cells and model membranes. First, the integrity of S. aureus membrane was evaluated by fluorescence microscopy. It was observed an increase in the permeability of cells that was dependent on the EO concentration as well as the incubation time. For a deep evaluation of the action of the EO on the lipids, its effect on the membrane fluidity was evaluated on DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine): DMPG (1,2-dimyristoyl-sn-glycero-3-phospho-1'-rac-glycerol) (5:1) liposomes by dynamic scattering light and by using Laurdan doped liposomes. The results indicate that EO produces changes in lipid membrane packing, increasing the fluidity, reducing the cooperative cohesive interaction between phospholipids and increasing access of water or the insertion of some components of the EO to the interior of the membrane. In addition, the potential effect of EO on intracellular targets, as the increase of cytosolic reactive oxygen species (ROS) and DNA damage, were evaluated. The EO was capable of increasing the production of ROS as well as inducing a partial degradation of DNA. Finally, the effect of EO on S. aureus biofilm was tested. These assays showed that EO was able to inhibit the biofilm formation, and also eradicate preformed biofilms. The results show, that the EO seems to have several bacterial targets involved in the antibacterial activity, from the bacterial membrane to DNA. Furthermore, the antibacterial action affects not only planktonic cells but also biofilms; reinforcing the potential application for this EO.

Modification of bacterial cell membrane dynamics and morphology upon exposure to sub inhibitory concentrations of ciprofloxacin

Ciprofloxacin (CPX), a second generation fluoroquinolone antibiotic, is used as a primary antibiotic for treatment against gastroenteritis, drug-resistant tuberculosis, and malignant otitis externa. CPX is a broad spectrum antibiotic that targets the DNA gyrase of both Gram-positive and Gram-negative bacteria. Irrational and improper usage of CPX results in emergence of CPX resistant organisms emphasizing the importance of using lethal doses of CPX. Here, we have systematically analysed the effect of CPX at sub lethal concentrations on live E. coli membrane and growth dynamics. As a result of CPX interaction at sub-lethal concentrations, we detected filamentation of the bacterial cells during cell division. Although CPX is a DNA targeting antibiotic and did not result in considerable increase of live E. coli cell surface roughness, we observed significant enhancement in the lipid diffusion coefficients possibly due to disrupted lipid packing or altered lipid composition. Interestingly, we seem to observe slightly higher extent of lipid diffusion alteration when bacterial inner membrane specific label FM4-64 was used in comparison to the non-specific membrane dye. Both these results are contrary to that observed in bacterial cells for colistin, a membrane targeting antibiotics. Our work highlights the need for using multiple, complementary surface and depth sensitive techniques to obtain information on the realistic nature of bacterial cell membrane remodelling due to non-membrane targeting antibiotics. Our work could have implications for identification of potential biomembrane markers at sub-lethal concentrations even for antibiotics which are non-membrane targeting that could help in unravelling pathways for emergence of antimicrobial resistance.

Antimicrobial peptide GL13K immobilized onto SLA-treated titanium by silanization: antibacterial effect against methicillin-resistant Staphylococcus aureus (MRSA)

Infection is the main reason for implant failure, and the incidence of drug-resistant bacterial infection has increased in recent years. Further, methicillin-resistant Staphylococcus aureus (MRSA)-related implant infection has become a serious worldwide threat. New strategies, other than antibiotics, to tackle drug-resistance, are of high clinical significance. Antimicrobial peptides show clear superiority over conventional antibiotics in inhibiting drug-resistant bacteria. In the present study, we combined the antimicrobial peptide, GL13K, with sandblasting and acid-etching (SLA)-treated titanium using a silane coupling agent. Field emission scanning electron microscopy images showed the morphology of the coating. Attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results confirmed loading of GL13K, and the hydrophilicity of the SLA-GL13K coating was evaluated by water contact angle analysis. The releasing study of samples showed that the coating has a sustained releasing profile. SLA-GL13K coating exhibited strong contact- and release-killing abilities against MRSA, E. coli, and S. aureus. Meanwhile, Cell Counting Kit 8 analysis and examination of cell morphology demonstrated that the SLA-GL13K coating had good cytocompatibility at antibacterial concentrations. Overall, all these results suggest that SLA-GL13K coating can be successfully fabricated using silanization, and is a promising candidate for controlling MRSA-induced implant-related infection.

Phytochemical content and potential health applications of pecan [Carya illinoinensis (Wangenh) K. Koch] nutshell

BACKGROUND

The pecan nutshell contains phytochemicals with various biological activities that are potentially useful in the prevention or treatment of diseases such as cancer, diabetes, and metabolic imbalances associated with heart diseases.

OBJECTIVE

To update this topic by means of a literature review and include those that contribute to the knowledge of the chemical composition and biological activities of pecan nutshell, particularly of those related to the therapeutic potential against some chronic degenerative diseases associated with oxidative stress.

METHOD

Exhaustive and detailed review of the existing literature using electronic databases.

CONCLUSION

The pecan nutshell is a promising natural product with pharmaceutical uses in various diseases. However, additional research related to the assessment of efficient extraction methods and characterization, particularly the evaluation of the mechanisms of action in new in vivo models, is necessary to confirm these findings and development of new drugs with therapeutic use.

Design and construction of novel biocatalyst for bioprocessing: Recent advances and future outlook

Bioprocess, a biocatalysis-based technology, is becoming popular in many research fields and widely applied in industrial manufacturing. However, low bioconversion, low productivity, and high costs during industrial processes are usually the limitation in bioprocess. Therefore, many biocatalyst strategies have been developed to meet these challenges in recent years. In this review, we firstly discuss protein engineering strategies, which are emerged for improving the biocatalysis activity of biocatalysts. Then, we summarize metabolic engineering strategies that are promoting the development of microbial cell factories. Next, we illustrate the necessity of using the combining strategy of protein engineering and metabolic engineering for efficient biocatalysts. Lastly, future perspectives about the development and application of novel biocatalyst strategies are discussed. This review provides theoretical guidance for the development of efficient, sustainable, and economical bioprocesses mediated by novel biocatalysts.

Physicochemical Features and Peculiarities of Interaction of AMP with the Membrane

Antimicrobial peptides (AMPs) are anti-infectives that have the potential to be used as a novel and untapped class of biotherapeutics. Modes of action of antimicrobial peptides include interaction with the cell envelope (cell wall, outer- and inner-membrane). A comprehensive understanding of the peculiarities of interaction of antimicrobial peptides with the cell envelope is necessary to perform a rational design of new biotherapeutics, against which working out resistance is hard for microbes. In order to enable de novo design with low cost and high throughput, in silico predictive models have to be invoked. To develop an efficient predictive model, a comprehensive understanding of the sequence-to-function relationship is required. This knowledge will allow us to encode amino acid sequences expressively and to adequately choose the accurate AMP classifier. A shared protective layer of microbial cells is the inner, plasmatic membrane. The interaction of AMP with a biological membrane (native and/or artificial) has been comprehensively studied. We provide a review of mechanisms and results of interactions of AMP with the cell membrane, relying on the survey of physicochemical, aggregative, and structural features of AMPs. The potency and mechanism of AMP action are presented in terms of amino acid compositions and distributions of the polar and apolar residues along the chain, that is, in terms of the physicochemical features of peptides such as hydrophobicity, hydrophilicity, and amphiphilicity. The survey of current data highlights topics that should be taken into account to come up with a comprehensive explanation of the mechanisms of action of AMP and to uncover the physicochemical faces of peptides, essential to perform their function. Many different approaches have been used to classify AMPs, including machine learning. The survey of knowledge on sequences, structures, and modes of actions of AMP allows concluding that only possessing comprehensive information on physicochemical features of AMPs enables us to develop accurate classifiers and create effective methods of prediction. Consequently, this knowledge is necessary for the development of design tools for peptide-based antibiotics.

Zeta potential beyond materials science: Applications to bacterial systems and to the development of novel antimicrobials

This review summarizes the theory of zeta potential (ZP) and the most relevant data about how it has been used for studying bacteria. We have especially focused on the discovery and characterization of novel antimicrobial compounds. The ZP technique may be considered an indirect tool to estimate the surface potential of bacteria, a physical characteristic that is key to maintaining optimal cell function. For this reason, targeting the bacterial surface is of paramount interest in the development of new antimicrobials. Surface-acting agents have been found to display a remarkable bactericidal effect and have simultaneously revealed a low tendency to trigger resistance. Changes in the bacterial surface as a result of various processes can also be followed by ZP measurements. However, due to the complexity of the bacterial surface, some considerations regarding the assessment of ZP must first be taken into account. Evidence on the application of ZP measurements to the characterization of bacteria and biofilm formation is presented next. We finally discuss the feasibility of using the ZP technique to assess antimicrobial-induced changes in the bacterial surface. Among these changes are those related to the interaction of the agent with different components of the cell envelope, membrane permeabilization, and loss of viability.