Improvement Of Antimicrobial Activity Research Articles

Facile Halogenation of Antimicrobial Peptides As Demonstrated by Producing Bromotryptophan-Labeled Nisin Variants with Enhanced Antimicrobial Activity.

Antimicrobial peptides (AMPs) have raised significant interest, forming a potential new class of antibiotics in the fight against multi-drug-resistant bacteria. Various AMPs are ribosomally synthesized and post-translationally modified peptides (RiPPs). One post-translational modification found in AMPs is the halogenation of Trp residues. This modification has, for example, been shown to be critical for the activity of the potent AMP NAI-107 from Actinoallomurus. Due to the importance of organohalogens, establishing methods for facile and selective halogen atom installation into AMPs is highly desirable. In this study, we introduce an expression system utilizing the food-grade strain Lactococcus lactis, facilitating the efficient incorporation of bromo-Trp (BrTrp) into (modified) peptides, exemplified by the lantibiotic nisin with a single Trp residue or analogue incorporated at position 1. This provides an alternative to the challenges posed by halogenase enzymes, such as poor substrate selectivity. Our method yields expression levels comparable to that of wild-type nisin, while BrTrp incorporation does not interfere with the post-translational modifications of nisin (dehydration and cyclization). One brominated nisin variant exhibits a 2-fold improvement in antimicrobial activity against two tested pathogens, including a WHO priority pathogen, while maintaining the same lipid II binding and bactericidal activity as wild-type nisin. The work presented here demonstrates the potential of this methodology for peptide halogenation, offering a new avenue for the development of diverse antimicrobial products labeled with BrTrp.

Apoptin NLS2 homodimerization strategy for improved antibacterial activity and bio-stability.

The emergence of antibiotic resistance prompts exploration of viable antimicrobial peptides (AMPs) designs. The present study explores the antimicrobial prospects of Apoptin nuclear localization sequence (NLS2)-derived peptide ANLP (PRPRTAKRRIRL). Further, we examined the utility of the NLS dimerization strategy for improvement in antimicrobial activity and sustained bio-stability of AMPs. Initially, the antimicrobial potential of ANLP using antimicrobial peptide databases was analyzed. Then, ANLP along with its two homodimer variants namely ANLP-K1 and ANLP-K2 were synthesized and evaluated for antimicrobial activity against Escherichia coli and Salmonella. Among three AMPs, ANLP-K2 showed efficient antibacterial activity with 12µM minimum inhibitory concentration (MIC). Slow degradation of ANLP-K1 (26.48%) and ANLP-K2 (13.21%) compared with linear ANLP (52.33%) at 480min in serum stability assay indicates improved bio-stability of dimeric peptides. The AMPs presented no cytotoxicity in Vero cells. Dye penetration assays confirmed the membrane interacting nature of AMPs. The zeta potential analysis reveals effective charge neutralization of both lipopolysaccharide (LPS) and bacterial cells by dimeric AMPs. The dimeric AMPs on scanning electron microscopy studies showed multiple pore formations on the bacterial surface. Collectively, proposed Lysine scaffold dimerization of Apoptin NLS2 strategy resulted in enhancing antibacterial activity, bio-stability, and could be effective in neutralizing the off-target effect of LPS. In conclusion, these results suggest that nuclear localization sequence with a modified dimeric approach could represent a rich source of template for designing future antimicrobial peptides.

Effect of Spacer Length Modification of the Cationic Side Chain on the Energetics of Antimicrobial Peptide Binding to Membrane-Mimetic Bilayers.

Understanding the mechanism of action of the antimicrobial peptide (AMP) in terms of its structure and energetics is the key to designing new potent and selective AMPs. Recently, we reported a membranolytic 14-residue-long lysine-rich cationic antimicrobial peptide (LL-14: NH3+-LKWLKKLLKWLKKL-CONH2) against Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus, which is limited by cytotoxicity and expected to undergo facile protease degradation. Aliphatic side-chain-length modification of the cationic amino-acid residues (Lys and Arg) is a popular strategy for designing protease-resistant AMPs. However, the effect of the peptide side-chain length modifications on the membrane binding affinity and its relation to the atomic structure remain an unsolved problem. We report computer simulations that quantitatively calculated the difference in peptide binding affinity to membrane-mimetic-bilayer models (bacterial: 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE)/1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) bilayer and mammalian: 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer) upon decreasing or increasing the spacer length of the cationic lysine residues of LL-14 (as well as their arginine analogues). We show that the peptide/bilayer interaction energetics varies drastically in response to spacer length modification. The strength of peptide discrimination depends strongly on the nature of the bilayer (bacterial or mammalian mimetic model). An increase in the lysine spacer length by one carbon (i.e., homolysine analogue of LL-14) is weakly/strongly disfavored by the bacterial/mammalian-membrane-mimetic bilayer. Recently, we have demonstrated an excellent correlation between the antimicrobial activity of the membranolytic cationic peptides and their binding affinity to membrane-mimetic-bilayer models. Thus, the homolysine analogue of LL-14 is a promising noncytotoxic AMP with conserved activity. On the other hand, homoarginine analogue (arginine spacer length increment by a single carbon) was preferred by both the bacteria and the mammalian mimetic bilayers and displayed the strongest affinity for the former among the peptides studied in this work. Thus, the promising most potent homoarginine analogue is likely to be cytotoxic. Shortening the Lys/Arg side chain to a three-carbon spacer (Dab/Agb) improves the binding affinity to bacterial and mammalian-membrane-mimetic bilayers. Arginine and arginine-derivative peptides exhibited stronger binding affinity to the bilayers relative to the lysine analogue. The results provide a plausible explanation to the previous experimental observations, viz., superior antimicrobial activity of the arginine peptides relative to Lys peptides and the improvement of antimicrobial activity upon substitution of Lys with Dab in the cationic peptides. The simulations revealed that the small change in the peptide hydrophobicity by Lys/Arg spacer length modification could drastically alter the energetics of peptide/bilayer binding by fine-tuning the electrostatic interactions. The energetics underlying the peptide selectivity by simple membrane-mimetic bilayer models may be beneficial for designing new selective and protease-resistant AMPs.

β-Turn editing in Gramicidin S: Activity impact on replacing proline α-carbon with stereodynamic nitrogen

Gramicidin S, natural antimicrobial peptide is used commercially in medicinal lozenges for sore throat and Gram-negative and Gram-positive bacterial infections. However, its clinical potential is limited to topical applications because of its high red blood cells (RBC) cytotoxicity. Given the importance of developing potential antibiotics and inspired by the cyclic structure and druggable features of Gramicidin S, we edited proline α-carbon with stereodynamic nitrogen to examine the direct impact on biological activity and cytotoxicity with respect to prolyl counterpart. Natural Gramicidin S (12), proline-edited peptides 13–16 and wild-type d-Phe-d-Pro β-turn mimetics (17 and 18) were synthesized using solid phase peptide synthesis and investigated their activity against clinically relevant bacterial pathogens. Interestingly, mono-proline edited analogous peptide 13 showed moderate improvement in antimicrobial activity against E. coli ATCC 25922 and K.pneumoniae BAA 1705 as compared to Gramicidin S. Furthermore, proline edited peptide 13 exhibited equipotent antimicrobial effect against MDR S. aureus and Enterococcus spp. Analysis of cytotoxicity against VERO cells and RBC, reveals that proline edited peptides showed two-fivefold lesser cytotoxicity than the counterpart Gramicidin S. Our study suggests that introducing single azPro/Pro mutation in Gramicidin S marginally improved the activity and lessens the cytotoxicity as compared with the parent peptide.

Synergistic effects of zinc borate and graphene on enhanced thermal stability and antimicrobial properties of poly(methyl methacrylate)

AbstractThe use of graphene nanoplatelets (GnP) as reinforcing material for thermoplastic polymer matrices, polymethyl methacrylate (PMMA) and zinc borate (ZnB), as an antimicrobial and fire‐retardant agent was studied. PMMA‐ZnB and PMMA‐GnP‐ZnB (ZG) composite films were fabricated with different ZnB concentrations (2.5, 5, 10 wt%) by solvent casting method using acetone. The effect of additives on the antimicrobial activity, thermal and mechanical properties, and surface morphologies of the composites were investigated. Antimicrobial surface activity tests were conducted against seven microorganisms, including bacterial and fungal species. An improvement in antimicrobial activity by up to 99.99% with increasing ZnB content was observed. Thermal stability was increased with increasing concentration of ZnB and a combination of ZnB and GnP additions. 10% ZG‐based composites increased the % char residue value of PMMA from 0.5% to 9.3%. The incorporation of the ZnB and GnP into the PMMA matrix resulted in an increase in the calculated limiting oxygen index (LOI). 10% and 50% weight loss temperature increased by 11.7°C and 3.7°C, respectively, for 10% ZG composites. The Young's modulus of the composites increased with increasing ZnB and a combination of ZnB and GnP loading (increasing by 16% to 2033 MPa with the addition of 10 wt% ZG). The commercial application for this study would be in high touch and piano black automotive interior, construction, and medical applications.

Physicochemical characterization tungsten oxide modified hydroxyapatite embedded into polylactic acid nanocomposite for biomedical applications

To compensate for the feeble antimicrobial potential of hydroxyapatite (HAp), the compound has been incorporated into different nanocomposites (NCs) in addition to powder and fibrous structure. Hydroxyapatite (HAp)/tungsten oxide/graphene oxide (GO) ternary nanocomposite introduces a significant enhance in the cell viability to 96.7 ± 3% towards the osteoblast cells. The chemical compositions were approved by various analytical techniques such as XRD, FTIR, XPS, and EDS. TEM shows well-defined, rod-like HAp grains. The triple ingredient HAp/WO3/GO nano-composite exhibits an 22.8 nm grain size. FESEM introduces grain shape deviation via changing HAp additives from semi-spherical to needle-like with macro-porous structure within the composite of HAp/WO3/GO. Moreover, compatibility of ternary nanocomposite inside the PLA environment led to decrease in the contact angle of the nanofibrous structure reached 16.5 ± 4.4°. The combination of HAp and organic/inorganic elements might represent a good characterization for the target biological applications. HAp/WO3/GO composite exhibits a significant improvement in anti-microbial activity to be around 85.6 ± 1.6 % and 110.1 ± 2.0 % in for E. coli and S. aureus.

The "steric-like" inhibitory effect and mechanism of doxycycline on florfenicol metabolism: Interaction risk.

Most of the studies on doxycycline (DOX) and florfenicol (FF) remain focused on the improvement of antimicrobial activity and antimicrobial spectrum, and there is no relevant report on whether there is interaction between the two drugs after the combination. This research study evaluated the effect of DOX on FF metabolism in vitro and its mechanisms. The findings of this study showed that DOX inhibits FF metabolism in two ways. Firstly, DOX significantly inhibits the expression of CYP3A29, leading to the slower metabolism of FF; secondly, DOX affects the binding of FF to R106 and R372 by competing for the R372 and/or by a "steric-like effect", thus slowing down FF metabolism, which may increase the residual concentration of FF in edible tissues of food producing animals.

Antimicrobial activity of mesoporous organic functionalized hexagon Fe3O4 nanosheets for wastewater treatment

Nano iron oxide has shown great potential to function as a universal and low-cost antimicrobial agent. In this work, we fabricated a new class of mesoporous hexagon magnetic iron oxide nanosheets (HMI-NS) modified by 3-aminopropyltriethoxysilane (APTES) through a simple synthesis route as a novel vehicle tracking building (VTB) antimicrobial agent. The VTB-MHI-NSs had a uniform platform-like structure with an average size of 45 nm and well-scattered active sites in the inner core and saline shell with microbicidal effect. Tests revealed that the modification of iron oxide nanosheets caused an improvement in antimicrobial activity against bacteria and fungi. The developed bioactive behavior of The VTB-MHI-NSs can be due to the system architectures, arrangement of crystal atomic-scale, and mesopore windows. This organically functionalized tailoring of The VTB-MHI-NSs can influence the particle size, shape, and surface properties, thereby creating significant extracellular interactions and exerting intracellular effects that cause antimicrobial activity. The appropriate functionalization of the hexagonal outer surface of the mesopore windows enabled the modulation of loading and microbial cell interaction and played a key role in offering sustained platform-like nanosheets that attached to the microbe, causing cell death. Therefore, the mesoporous organic functionalized hexagon iron oxide nanosheets can be considered in water future clean-up processes.

Immobilization of Polyoxometalate-Ionic Liquid on Coconut Shell Nanoporous Carbon Support: An improved material for water purification

Access to clean water by all is one of the UN Sustainable Development Goals. To achieve this, there is need to prepare sustainable materials for efficient water purification. This research aims to immobilize the Polyoxomatelate-Ionic Liquid (POM-IL), {[CH3(CH2)6]4N}7[α-PW11O39] on nanoporous carbon (NC) prepared from coconut shell to form an advanced material (POM-IL@NC) for effective removal of multiple contaminants from polluted water. The POM-IL@NC material was characterized by Fourier Transform-Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) Analysis and Brunauer-Emmett-Teller (BET) method. The material was then tested respectively for the removal of copper and lead using Atomic Absorption Spectroscopy (AAS) and methylene blue using Ultraviolet-Visible (UV-Vis) Spectroscopy from simulated polluted waters via adsorption. The material was further subjected to antimicrobial analysis. The results showed that the POM-IL@NC material performed better than the pristine NC in the removal of copper, lead and methylene blue from the contaminated water. The POM-IL@NC also exhibited significant improvement in antimicrobial activity than NC against Escherichia coli and Staphylococcus aureus. This shows that the new material could effectively be applied for multiple contaminants treatment of polluted water.

An Efficient Approach for the Design and Synthesis of Antimicrobial Peptide-Peptide Nucleic Acid Conjugates.

Peptide-Peptide Nucleic Acid (PNA) conjugates targeting essential bacterial genes have shown significant potential in developing novel antisense antimicrobials. The majority of efforts in this area are focused on identifying different PNA targets and the selection of peptides to deliver the peptide-PNA conjugates to Gram-negative bacteria. Notably, the selection of a linkage strategy to form peptide-PNA conjugate plays an important role in the effective delivery of PNAs. Recently, a unique Cysteine- 2-Cyanoisonicotinamide (Cys-CINA) click chemistry has been employed for the synthesis of cyclic peptides. Considering the high selectivity of this chemistry, we investigated the efficiency of Cys-CINA conjugation to synthesize novel antimicrobial peptide-PNA conjugates. The PNA targeting acyl carrier protein gene (acpP), when conjugated to the membrane-active antimicrobial peptides (polymyxin), showed improvement in antimicrobial activity against multidrug-resistant Gram-negative Acinetobacter baumannii. Thus, indicating that the Cys-CINA conjugation is an effective strategy to link the antisense oligonucleotides with antimicrobial peptides. Therefore, the Cys-CINA conjugation opens an exciting prospect for antimicrobial drug development.

Mesoporous Silica and Titania-Based Materials for Stability Enhancement of Polyphenols.

To improve phytochemical stability, polyphenolic extracts prepared from Salvia officinalis L., which is a valuable source of phytocompounds with health benefits, were embedded into mesopores of silica, titania, or titania-ceria materials. Ethanolic and hydroalcoholic extracts were prepared by conventional, microwave- or ultrasound-assisted extraction. The influence of the extraction conditions on chemical profile, radical scavenger activity (RSA), and antimicrobial potential of the extracts was assessed. The extracts were characterized by spectrophotometric determination of total polyphenols, flavonoids, chlorophyll pigment contents, as well as RSA. A reverse phase HPLC- PDA analysis was performed for the identification and quantification of extract polyphenols. The extract-loaded materials exhibited an enhanced RSA compared to the free extract after several months of storage, resulting in better polyphenol stability over time following embedding into a mesoporous matrix. Selected extracts free and embedded into mesoporous support were tested against Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, and Staphylococcus aureus ATCC 25923; the best antimicrobial activity was obtained for S. aureus. A slight improvement in antimicrobial activity was observed for the ethanolic extract prepared by ultrasound-assisted extraction following embedding into the TiO2 matrix compared to MCM-41 silica due to the support contribution.

Physicochemical and microbiological characterization of pectin-based gelled emulsions coating applied on pre-cut carrots

Two antimicrobial formulations composed of Biosecur F440D (citrus extract) and a mixture of four essential oils (EOs) entrapped in pectin-based matrix were characterized by Fourier-transform infrared spectroscopy (FTIR). The effect of pectin-based matrix on active compounds’ release and their stability during storage time were also evaluated. Furthermore, shelf-life of pre-cut carrots coated with gelled emulsions and its antimicrobial activity against Listeria monocytogenes and Penicillium chrysogenum were assessed. Based on FTIR analysis, entrapment of Biosecur F440D in pectin matrix was obtained especially by hydrogen bonding and CH stretching. A strong asymmetric –CH3 stretching in alkyl groups were also observed for the entrapment of mixture of EOs in pectin matrix. The entrapment of bioactive ingredients in pectin matrix slowed down the release behavior for both formulations and gave a better stability of total phenols content and color especially in Biosecur F440D based emulsion. Application of gelled emulsion on pre-cut carrots improved the shelf-life by 1 day as compared to untreated carrot for Biosecur-based gelled emulsion containing EOs and by 2 days for EOs-based gelled emulsion containing Biosecur F440D. An improvement in antimicrobial activity against L. monocytogenes and P. chrysogenum was also observed for both emulsions and their respective gelled emulsions.

IsCT-based analogs intending better biological activity.

IsCT1-NH2 is a cationic antimicrobial peptide isolated from the venom of the scorpion Opisthacanthus madagascariensis that has a tendency to form an α-helical structure and shows potent antimicrobial activity and also inopportunely shows hemolytic effects. In this study, five IsCT1 (ILGKIWEGIKSLF)-based analogs with amino acid modifications at positions 1, 3, 5, or 8 and one analog with three simultaneous substitutions at the 1, 5, and 8 positions were designed. The net charge of each analog was between +2 and +3. The peptides obtained were characterized by mass spectrometry and analyzed by circular dichroism for their structure in different media. Studies of antimicrobial activity, hemolytic activity, and stability against proteases were also carried out. Peptides with a substitution at position 3 or 5 ([L]3 -IsCT1-NH2 , [K]3 -IsCT1-NH2 , or [F]5 -IsCT1-NH2 ) showed no significant change in an activity relative to IsCT1-NH2 . The addition of a proline residue at position 8 ([P]8 -IsCT1-NH2 ) reduced the hemolytic activity as well as the antimicrobial activity (MIC ranging 3.13-50 μmol L-1 ), and the addition of a tryptophan residue at position 1 ([W]1 -IsCT1-NH2 ) increased the hemolytic activity (MHC = 1.56 μmol L-1 ) without an improvement in antimicrobial activity. The analog [A]1 [F]5 [K]8 -IsCT1-NH2 , which carries three simultaneous modifications, presented increasing or equivalent values in antimicrobial activity (MIC approximately 0.38 and 12.5 μmol L-1 ) with a reduction in hemolytic activity. In addition, this analog presented the best resistance against proteases. This kind of strategy can find functional hotspots in peptide molecules in an attempt to generate novel potent peptide antibiotics.

In Vitro and In Vivo Antimicrobial Activity of Antibiotic-Conjugated Carriers with Rapid pH-Responsive Release Kinetics.

Two representative antibiotics, cephradine (CP) and moxifloxacin (MX), are covalently conjugated with a β-cyclodextrin (β-CD)-based carrier via pH-responsive 1-methyl-2-(2'-carboxyethyl) maleic acid amide (MCM) linkers with excellent conjugation efficiency via simple mixing. At pH 5.5, 90% and 80% of the CP and MX, respectively, are released from the carriers within 30 min, in contrast with the much-delayed release profile at pH 7.4. The in vitro inhibitory effect of β-CD-MCM-CP on the growth of Staphylococcus aureus is significantly lower than that of free CP at pH 7.4, but it reaches the level of free CP at pH 5.5. Moreover, S. aureus develops significant CP resistance after pretreatment with free CP, whereas the initial CP sensitivity is maintained after pretreatment with β-CD-MCM-CP at pH 7.4. However, β-CD-MCM-MX exhibits no such pH-responsive activity against Bacteroides fragilis, probably due to the insufficient stability of the MX conjugation at pH 7.4. In nondiabetic and diabetic mouse models, β-CD-MCM-CP significantly reduces the subcutaneous abscess scores and the bacterial counts in the abscess, although this represents only a marginal improvement in antimicrobial activity compared to free CP.

Nano-complexation of ε-poly-l-lysine with DNA: Improvement of antimicrobial activity under high phosphate conditions.

ε-Poly-l-lysine (PL) has high antimicrobial activity and a wide antimicrobial spectrum and is applied broadly in the food industry. However, PL may lose part of its activity in phosphate systems, which are typically used in seafood processing. To enhance antimicrobial activity under high phosphate conditions, DNA/PL nanoparticles were fabricated via the nanoprecipitation method. The DNA/PL nanoparticle size was smallest when the ethanol to water ratio was 7:1, and the mean diameter was 101 nm. UV-vis showed hypochromism and a redshift of the DNA in the presence of PL, indicating an intercalative interaction between DNA and PL. FTIR spectroscopy revealed that strong hydrogen bonds and hydrophobic interactions were involved in DNA/PL nanoparticle formation. Compared with that of PL, the antimicrobial activity of the nanoparticles against S. aureus, B. subtilis, and E. coli was enhanced. Additionally, the DNA/PL nanoparticles still retained higher antimicrobial activity in the phosphate system than free PL. The antimicrobial mechanistic analysis provided evidence that the DNA/PL nanoparticles showed high bioactivity due to cell membrane damage. This work provides a potential method to enhance the antimicrobial activity of PL under adverse conditions, which can promote the application of PL in seafood containing phosphate compounds.

One Step Thermochromic Pigment Printing and Ag NPs Antibacterial Functional Finishing of Cotton and Cotton/PET Fabrics

One step thermochromic pigment printing and antibacterial functionality of cotton (100 %) and cotton/polyester blend (50/50 %) were demonstrated in this study. The improvement in antimicrobial activity against G+ve (Bacillus cereus) and G-ve (E. coli), and pigment printability were achieved by inclusion of Ag-NPs (30 g/kg) into pigment printing paste followed by printing and microwave curing at 700 W for 5 min. Modes of interactions were proposed, and surface modification was also confirmed by SEM and EDX analysis that proved the presence of Ag-NPs in cotton and cotton/ polyester blended samples. The results indicated that the colour fastness to wash and rubbing was excellent, the surface roughness reduced, and exhibited good antibacterial activity against Bacillus cereus and E. coli bacteria.

Development of Multi-functional Properties on Cotton Fabric by In Situ Application of TiO2 and ZnO Nanoparticles

Cotton fabrics functionalized with different combinations of TiO2 and ZnO were evaluated for multifunctional properties including UV protection, antimicrobial and self-cleaning. The ZnO nanoparticles synthesized using sol gel method were applied on cotton fabric by pad-dry-cure method and TiO2 was deposited in situ. The deposition of both TiO2 and ZnO was examined and confirmed by SEM and EDX analysis. Application of both metal oxides resulted in good improvement in UV protection of treated fabrics. The fabrics which were finished with combination of both Zinc and Titanium oxides, showed UPF rating of 50+ as compared to UPF rating of untreated cotton, which was only 5. The same fabrics also showed higher self-cleaning extent as compared to untreated cotton fabric. It was found that the sequence of application of ZnO and TiO2 affected the antimicrobial activity of the finished fabric and also the durability. When application of TiO2 was followed by ZnO, the combination resulted in development of excellent antimicrobial property against Escherichia coli (~ 99% colony reduction) which was retained after 10 wash cycles. However, when application of ZnO nanoparticles was followed by application of TiO2, the improvement in antimicrobial activity was found to be moderate (~ 48% colony reduction) and had poor wash durability. Hence, the specific sequence of application of these metals oxides can be utilized for obtaining good durability of the multifunctional properties on cotton fabric.

Exploring Peptide Sequence Space Using Artificial Intelligence for Antimicrobial Peptides

The number of effective antibiotics is rapidly decreasing due to the emergence of resistant bacteria, which necessitates the development of not only new, but novel strategies for developing antibiotics. Antimicrobial peptides (AMPs) are considered to be a promising new class of antibiotics, and effective strategies to predict potential candidates are still actively sought after. Here, we present a closed-loop artificial intelligence-based approach that combines an in silico genetic algorithm, machine learning prediction, and in vitro evaluation to improve the antimicrobial activity of peptides. Starting with a 13-mer natural AMP, 44 highly potent peptides were identified achieving up to a ca. 160-fold increase in antimicrobial activity within just three rounds of experiments. During these experiments, the conformation of the peptides selected was observed to alter from a random coil to α-helical form through the optimization process, and this is thought to significantly contribute to the improvement of antimicrobial activity. This strategy therefore shows it is possible to accelerate the discovery of antimicrobial peptides within a relatively small number of experiments, and to explore broad sequence and structural space.

Effect of heat on grape marc extract

Food spoilage is a major global concern, and solutions involving green active packaging are being actively sought. Grape marc is a by-product of the wine industry, and is rich in tannins with antioxidant and antimicrobial activity. For use in melt blending with plastics such as polyethylene, the impact of heating a grape tannin extract to 150°C was evaluated. While there was a loss in total phenolic content after heating, this did not lead to a loss in functionality. There was an improvement in antioxidant activity from 65.3 ± 0.6% to 70.8 ± 1.3% DPPH radicals scavenged, and a significant improvement in antimicrobial activity. Against E. coli, the activity improved by 35%, while against S. aureus there was improvement of 60%. FT-IR analysis showed no degradation of the extract when heated to 150°C, other than some disruption of hydrogen bonds within the condensed tannin network.

Green synthesis and characterisation of antioxidant-tagged gold nanoparticle (X-GNP) and studies on its potent antimicrobial activity

ABSTRACTAlternanthera philoxeroides (Mart.), a weed, mainly from tropical origin and easily available worldwide. People used to eat it as a food mainly in South Africa. In our previous report we have thoroughly characterise several important phenolics, monoterpene and phenylpropane from methanol soluble fraction of Alternenthera leaves (fraction X) and also reported their α-glucosidase inhibitory, antimicrobial and antioxidant activities. All these isolated natural compounds are well characterised and widely studied. In our present study we try to use this beneficial fraction (named fraction X) in green synthesis of gold nanoparticles (X-GNP). We also try to explore the beneficial aspects of green synthesis in comparison with commonly used chemical synthesis method (GNP) in context with their antimicrobial activity. UV/Vis spectroscopy, DLS, Zeta potential, FT-IR, EDAX and other microscopic techniques namely: SEM, AFM were used to characterise the synthesised nanoparticles. Different important microbial strains were used to evaluate the antimicrobial activity of prepared nanoparticles. Overall the studies suggest successful synthesis of green nanoparticles (X-GNP) and also showed the improvement in antimicrobial activity of X-GNP nanoparticles.