Synthesis, electrospinning, and molecular docking of poly(methyl methacrylate) Schiff bases and their applications as polymeric antimicrobial agents and for dye removal

The antibacterial activity of a variety of modified poly(methyl methacrylate) Schiff bases against common microbial infections and removal of methylene blue (MB) dye were screened. The Schiff bases were synthesized from the reaction of the modified (PMMA) with vanillin (PMMA)Van and cinnamaldehyde (PMMA)Cin. By using Fourier transformer infrared (FT-IR), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), the structures of the nanofibers of the synthesized Schiff bases were confirmed. The modified Kirky-Bauer method was used to screen the antibacterial activities of all the obtained materials against various bacterial species, including gram-positive bacterial (Bacillus subtilis (4k1p), Staphylococcus aureus), Gram-negative bacteria (Escherichia coli (7ab3), Pseudomonas aeruginosa). Inhibition zones against gram-positive bacteria ranged in diameter from 7 to 14 mm, whereas for the Gram-negative bacteria, the inhibition zones found to be ranged between 6 and 13 mm. With a minimum bactericidal concentration (MBC) of 8 mg/mL and a minimum inhibitory concentration (MIC) of 2 mg/mL, (PMMA)Van shown the greatest antibacterial activity. Lastly, molecular docking research was done to better understand the interactions between this series' targets and inhibitors for (PMMA)Van and (PMMA)Cin (4k1p and 7ab3). Molecular modeling of these surface-adsorbed polymers indicated that (PMMA)Van binds more strongly with Nitrogen than does (PMMA)Cin through extra hydrogen-bonding interactions. All the developed materials were evaluated for the removal of 0.1 g/L methylene blue dye (MB) from an aqueous solution. The elimination percentage of MB dye ranged from 26.67% by using 0.05 g powder of (PMMA)Cin to 85.63% by employing 0.05 g nanofibers of (PMMA)Van.

Membrane lytic activity of antibacterial ionenes, critical role of phosphatidylcholine (PC) and cardiolipin (CL)

Understanding the mechanism by which an antibacterial agent interacts with a model membrane provides vital information for better design of future antibiotics. In this study, we investigated two antibacterial polymers, hydrophilic C0-T-p and hydrophobic C8-T-p ionenes, known for their potent antimicrobial activity and ability to disrupt the integrity of lipid bilayers. Our hypothesize is that the composition of a lipid bilayer alters the mechanism of ionenes action, potentially providing an explanation for the observed differences in their bioactivity and selectivity. Calcein release experiments utilizing a range of liposomes to examine the impact of (i) cardiolipin (CL) to phosphatidylglycerol (PG) ratio, (ii) overall vesicle charge, and (iii) phosphatidylethanolamine (PE) to phosphatidylcholine (PC) ratio on the activity of ionenes were performed. Additionally, polymer-bilayer interactions were also investigated through vesicle fusion assay and the black lipid membrane (BLM) technique The activity of C0-T-p is strongly influenced by the amount of cardiolipin, while the activity of C8-T-p primarily depends on the overall vesicle charge. Consequently, C0-T-p acts through interactions with CL, whereas C8-T-p modifies the bulk properties of the membrane in a less-specific manner. Moreover, the presence of a small amount of PC in the membrane makes the vesicle resistant to permeabilization by tested molecules. Intriguingly, more hydrophilic C0-T-p retains higher membrane activity compared to the hydrophobic C8-T-p. However, both ionenes induce vesicle fusion and increase lipid bilayer ion permeability.

Effect of Cationic Groups on the Selectivity of Ternary Antimicrobial Polymers

Antimicrobial polymers (AMPs) have emerged as a promising approach to combat multidrug-resistant pathogens. Developed from binary polymers, which contain cationic and hydrophobic groups, ternary polymers are enhanced by adding neutral hydrophilic monomers to improve their biocompatibility. Cationic groups have attracted significant attention owing to their pivotal role in AMPs. Although many studies have investigated the effect of cationic groups on antimicrobial activity of binary AMPs, there is a lack of comprehensive and systematic evaluation for ternary AMPs. Therefore, a library of 31 statistical amphiphilic ternary polymers containing different cationic groups, including primary amine, guanidine and sulfonium groups was prepared to investigate the impact of cationic groups on antimicrobial activity and biocompatibility. We show that the cationic balance appears to be a critical factor influencing polymers' antibacterial activity and selectivity. Our results reveal that the polymers that have the ratio of the cationic groups ranging between 50-60%, coupled with a cationic/hydrophobic ratio in the range of [1.4-2] and an appropriate neutral hydrophilic/hydrophobic balance, exhibited the highest selectivity toward mammalian cells. Furthermore, selectivity can be improved with suitable cationic moieties and good neutral hydrophilic candidates. In the present study, a lysine-mimicking monomer and PEG chain were the best choices for cationic and hydrophilic sources to develop the most selective AMPs, displaying an impressive selectivity for HC₅₀ and IC₅₀ greater than 83 and 21, respectively. This study elucidates a structure-property-performance relationship for ternary AMPs, which contributes to the development of AMPs capable of selectively targeting gram-negative pathogens. This article is protected by copyright. All rights reserved.

Water-soluble anionic polychloramide biocides based on maleic anhydride copolymers

Our goal was to develop film-forming polymers to extend the antimicrobial lifetimes of cleaned and disinfected surfaces. Antimicrobial polymers were prepared by first reacting poly(ethylene-alt-maleic anhydride) with isopropylamine, partially consuming the anhydride groups, followed by hydrolysis to give water-soluble, highly anionic polyamide PC3. Chlorination with NaOCl gave PC3Cl with oxidative chlorine contents up to 9 wt%. Dried, 5 µm thick, PC3Cl films, gave log 4 reductions in the concentration of Escherichia coli or Staphylococcus aureus exposed to films. A unique feature of the maleic anhydride copolymer platform was the ability to form covalent grafts to surfaces via anhydride reactions. PC3 solution was impregnated into cellulosic filter paper, heated to form ester linkages with cellulose, followed by chlorination with sodium dichloroisocyanurate dihydrate giving grafted PC3Cl. The treated paper (0.3 wt% PC3Cl) gave a log 4 reduction of E. coli concentration in 30 min.

Antioxidant and antimicrobial material by grafting of L-arginine onto enzymatic poly(gallic acid)

Microwave-mediated grafting of L-Arg onto naturally derived and stable multiradical poly(gallic acid) (PGAL) in aqueous media has been successfully achieved. This polymeric material has no adverse effect in human cells as there is no hemolytic activity upon MTT and Neutral Red assays. The analytical and computational characterization studies carried out in this study describe a helical molecular structure with random incorporation of L-Arginine pendant groups from PGAL's backbone. The antioxidant properties of the precursor polymer are preserved as proved by the elimination of stable DPPH and hydroxyl radical scavenging, as well as the FRAP and ORAC assays. Regarding the latter, the oxygen radical inhibition is enhanced compared to PGAL, which is attributed to the guanidyl moieties. PGAL-g-L-Arg displays antimicrobial activity against Gram (+) Listeria monocytogenes and Staphylococcus aureus strains with a MIC of 0.8 g/L and a bacteriostatic effect against Gram (-) Escherichia coli. Additionally, scanning electron and confocal fluorescence microscopies as well as crystal violet colorimetric assay demonstrate that the mechanism involved in the bacterial inhibition is related to the formation of porous channels on the membrane, which is discussed according to the helical secondary structure of the polymer and the amino acid guanidyl moieties interacting to bacterial membranes.

Antimicrobial polymer modifications to reduce microbial bioburden on endotracheal tubes and ventilator associated pneumonia

Hospital associated infections (HAIs), infections acquired by patients during care in a hospital, remain a prevalent issue in the healthcare field. These infections often occur with the use of indwelling medical devices, such as endotracheal tubes (ETTs), that can result in ventilator-associated pneumonia (VAP). When examining the various routes of infection, VAP is associated with the highest incidence, rate of morbidity, and economic burden. Although ETTs are essential for the survival of patients requiring mechanical ventilation, their use comes with complications. The presence of an ETT in the airway impairs physiological host defense mechanisms for clearance of pathogens and provides a platform for oropharynx microorganism transport to the sterile tracheobronchial network. Antibiotics are administered to treat lower respiratory infections; however, they are not always effective and consequently can result in increased antibiotic resistance. Prophylactic approaches by altering the surface of ETTs to prevent the establishment and growth of bacteria have exhibited promising results. In addition, passive surface modifications that prevent bacterial establishment and growth, or active coatings that possess a bactericidal effect have also proven effective. In this review we aim to highlight the importance of preventing biofilm establishment on indwelling medical devices, focusing on ETTs. We will investigate successful antimicrobial modifications to ETTs and the future avenues that will ultimately decrease HAIs and improve patient care. STATEMENT OF SIGNIFICANCE: Infections that occur with indwelling medicals devices remain a constant concern in the medical field and can result in hospital-acquired infections. Specifically, ventilator associated pneumonia (VAP) occurs with the use of an endotracheal tube (ETT). Infections often require use of antibiotics and can result in patient mortality. Our review includes a summary of the recent collective work of antimicrobial ETT modifications and potential avenues for further investigations in an effort to reduce VAP associated with ETTs. Polymer modifications with antibacterial nature have been developed and tested; however, a focus on ETTs is lacking and clinical availability of new antimicrobial ETT devices is limited. Our collective work shows the successful and prospective applications to the surfaces of ETTs that can support researchers and physicians to create safer medical devices.

Facially amphiphilic polyionene biocidal polymers derived from lithocholic acid

Bacterial infections have become a global issue that requires urgent attention, particularly regarding to emergence of multidrug resistant bacteria. We developed quaternary amine-containing antimicrobial poly(bile acid)s that contain a hydrophobic core of lithocholic acid in the main-chain. Interestingly, by choosing appropriate monomers, these cationic polymers can form core-shell micelles. These polymers exhibited biocidal activity against both Gram-positive and Gram-negative bacterial species. It is demonstrated that the micelles can deliver hydrophobic antibiotics that functionally have dual antimicrobial activities. Cytotoxicity assays against HeLa cells showed dosage-dependent toxicity for polymers with longer linkers.

Characterisation of polyamide 11/copper antimicrobial composites for medical device applications

Direct incorporation of antimicrobial additive into the polymer matrix is a cost effective approach for the development of polymer/metal antimicrobial composites. Application of these antimicrobial composite systems for manufacturing medical devices addresses the issue of device related infections. In the present study, commercially available inorganic copper based additive, Plasticopper, was incorporated into a Polyamide 11(PA 11) matrix during the polymer processing stage. These polymer composites were evaluated for their morphological, mechanical, antimicrobial and ion release properties. Isothermal crystallisation studies showed that the copper additive acted as a nucleating agent and promoted faster crystallisation. Short term mechanical studies confirmed that the incorporation of copper has reinforcing effect on the composites with 5 and 10% copper loadings and did not adversely affect the short-term mechanical performance of the polymer composites. These composite systems were shown to be active against Escherichia coli ATCC 8739 with >99.99% reduction in bacterial population. Corresponding ion release profiles for these composites indicated long term antimicrobial activity.

Antimicrobial and antioxidant amphiphilic random copolymers to address medical device-centered infections

Microbial biofilms are known to support a number of human infections, including those related to medical devices. This work is focused on the development of novel dual-function amphiphilic random copolymers to be employed as coatings for medical devices. Particularly, copolymers were obtained by polymerization of an antimicrobial cationic monomer (bearing tertiary amine) and an antioxidant and antimicrobial hydrophobic monomer (containing hydroxytyrosol, HTy). To obtain copolymers with various amphiphilic balance, different molar ratios of the two monomers were used. (1)H NMR and DSC analyses evidenced that HTy aromatic rings are able to interact with each other leading to a supra-macromolecular re-arrangement and decrease the copolymer size in water. All copolymers showed good antioxidant activity and Fe(2+) chelating ability. Cytotoxicity and hemolytic tests evidenced that the amphiphilic balance, cationic charge density and polymer size in solution are key determinants for polymer biocompatibility. As for the antimicrobial properties, the lowest minimal inhibitory concentration (MIC = 40 μg/mL) against Staphylococcus epidermidis was shown by the water-soluble copolymer having the highest HTy molar content (0.3). This copolymer layered onto catheter surfaces was also able to prevent staphylococcal adhesion. This approach permits not only prevention of biofilm infections but also reduction of the risk of emergence of drug-resistant bacteria. Indeed, the combination of two active compounds in the same polymer can provide a synergistic action against biofilms and suppress reactive species oxygen (ROS), known to promote the occurrence of antibiotic resistance.

Therapeutic strategies to combat antibiotic resistance

With multidrug resistant bacteria on the rise, new antibiotic approaches are required. Although a number of new small molecule antibiotics are currently in the development pipeline with many more in preclinical development, the clinical options and practices for infection control must be expanded. Biologics and non-antibiotic adjuvants offer this opportunity for expansion. Nevertheless, to avoid known mechanisms of resistance, intelligent combination approaches for multiple simultaneous and complimentary therapies must be designed. Combination approaches should extend beyond biologically active molecules to include smart controlled delivery strategies. Infection control must integrate antimicrobial stewardship, new antibiotic molecules, biologics, and delivery strategies into effective combination therapies designed to 1) fight the infection, 2) avoid resistance, and 3) protect the natural microbiome. This review explores these developing strategies in the context of circumventing current mechanisms of resistance.

PHACOS, a functionalized bacterial polyester with bactericidal activity against methicillin-resistant Staphylococcus aureus

Biomaterial-associated infections represent a significant clinical problem, and treatment of these microbial infections is becoming troublesome due to the increasing number of antibiotic-resistant strains. Here, we report a naturally functionalized bacterial polyhydroxyalkanoate (PHACOS) with antibacterial properties. We demonstrate that PHACOS selectively and efficiently inhibits the growth of methicillin-resistant Staphylococcus aureus (MRSA) both in vitro and in vivo. This ability has been ascribed to the functionalized side chains containing thioester groups. Significantly less (3.2-fold) biofilm formation of S. aureus was detected on PHACOS compared to biofilms formed on control poly(3-hydroxyoctanoate-co-hydroxyhexanoate) and poly(ethylene terephthalate), but no differences were observed in bacterial adhesion among these polymers. PHACOS elicited minimal cytotoxic and inflammatory effects on murine macrophages and supported normal fibroblast adhesion. In vivo fluorescence imaging demonstrated minimal inflammation and excellent antibacterial activity for PHACOS compared to controls in an in vivo model of implant-associated infection. Additionally, reductions in neutrophils and macrophages in the vicinity of sterile PHACOS compared to sterile PHO implant were observed by immunohistochemistry. Moreover, a similar percentage of inflammatory cells was found in the tissue surrounding sterile PHACOS and S. aureus pre-colonized PHACOS implants, and these levels were significantly lower than S. aureus pre-colonized control polymers. These findings support a contact active surface mode of antibacterial action for PHACOS and establish this functionalized polyhydroxyalkanoate as an infection-resistant biomaterial.