Search

To palliate the appearance of antimicrobial resistance (AMR), the use of bactericidal agents acting differently than conventional antibiotics and the elimination of bacterial biofilm, are the two most promising strategies. Here, we integrated these two complementary strategies into new antimicrobial metal-enzyme nanoaggregates (NAs) of α-amylase and silver (αAgNAs) that are able to eliminate bacteria and their biofilm. The nanoparticle (NP) synthesis approach applied protein desolvation and laccase-mediated NP stabilization to innovatively produce catalytically active α-amylase nanoparticles (αNPs) for the elimination of the bacterial biofilm. At the same time, αNPs efficiently reduced silver for the incorporation of bactericidal Ag 0 and formation of the αAgNAs. The bactericidal and antibiofilm efficacies of αAgNAs were demonstrated by 5.4 and 6.1 log reduction of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, respectively, and more than 80% removal of their biofilms, coupled with high biocompatibility. The biofilm-αAgNA interaction was assessed by quartz crystal microbalance and atomic force microscopy revealing how the degradation of a settled biofilm by αAgNAs caused an increase of the biofilm water content, thus weakening the biofilm surface attachment and facilitating its removal. With the present work, we not only provide a new efficient antimicrobial material to face the AMR threat, but we also envisage that the newly established method for the synthesis of metal-enzyme NAs is potentially transferable to other biocatalysts to expand the enzyme NP toolbox.

Photosynthetic organisms use light to convert the inorganic matter in organic one. Photosynthetic process consists on several steps, and one of them involves plastoquinone (PQ) that acts as electron and proton shuttle between photosystem II and cytochrome. We prepared membranes that mimic the characteristics and composition of natural photosynthetic membranes and we characterized them using several techniques in order to obtain both the PQ molecules disposition in the membrane and their electrochemical behavior. The selected lipid was monogalactosyldiacylglycerol (MGDG) that represents the 50% of the lipid content of the thylakoid membrane. Both MGDG and PQ, and the MGDG:PQ mixtures have been studied using surface pressure-area isotherms and the presence of PQ alters the physical state and compactness of the MGDG matrix. Langmuir-Blodgett (LB) films have been obtained by transferring a monolayer that mimics half of the bilayer of a biological membrane. The AFM topographical characterization of the monolayers on mica indicates the presence of differentiated domains, corresponding to different physical states linked to the influence of the PQ content. Moreover, the electrochemical behavior of the monolayers has been studied when transferred on ITO, observing one main electrochemical process that is due to the diving position of PQ molecules in the lipid matrix.

Bacterial-mediated diseases are a major healthcare concern worldwide due to the rapid spread of antibiotic-resistant bacteria. One strategy to manage the bacterial infections while avoiding the emergence of resistant strains implies specific targeting and disruption of bacteria membranes. This work evaluates the potential of nanostructured biopolymer derivatives, nanocapsules (NCs), to disrupt the bacteria cell walls and effectively kill planktonic microorganisms. Two biopolymers, chitosan and cellulose, were chemically modified to synthesize derivatives with improved cationic character (thiolated chitosan and aminocellulose) prior to their processing into nanocapsules via a one-step sonochemical process. The interactions of NCs, displaying an average size of around 250 nm, with bacteria membrane were evaluated using two membrane models: Langmuir monolayers and liposome bilayers composed of a l-α-phosphatidylglycerol phospholipid extracted from Escherichia coli. NCs possessed improved membrane disturbing capacity in comparison to the nonprocessed biopolymer derivatives, by drastically increasing the monolayer fluidity and inducing more than 50% leakage of a dye inserted in the bilayered liposomes. In addition, membrane disturbance was directly proportional to the NCs cationic charge. Whereas evidence showed that thiolated chitosan and aminocellulose interacted with the bacteria membrane through a "carpet model", the NCs were found to induce larger surface defects and high local perturbance through a "detergent model". Importantly, the degree of disruption caused by the biopolymer derivatives and NCs correlated well with the antimicrobial capacity against Escherichia coli, selectively killing bacteria cells without imparting toxicity to human fibroblasts.

Ubiquinone (UQ) is one of the main electron and proton shuttle molecules in biological systems, and dipalmitoylphosphatidylcholine (DPPC) is one of the most used model lipids. Supported planar bilayers (SPBs) are extensively accepted as biological model membranes. In this study, SPBs have been deposited on ITO, which is a semiconductor with good electrical and optical features. Specifically, topographic atomic force microscopy (AFM) images and force curves have been performed on SPBs with several DPPC:UQ ratios to study the location and the interaction of UQ in the SPB. Additionally, cyclic voltammetry has been used to understand the electrochemical behavior of DPPC:UQ SPBs. Obtained results show that, in our case, UQ is placed in two main different positions in SPBs. First, between the DPPC hydrophobic chains, fact that originates a decrease in the breakthrough force of the bilayer, and the second between the two leaflets that form the SPBs. This second position occurs when increasing the UQ content, fact that eventually forms UQ aggregates at high concentrations. The formation of aggregates produces an expansion of the SPB average height and a bimodal distribution of the breakthrough force. The voltammetric response of UQ depends on its position on the bilayer.