Relevance of large litter bag burial for the study of leaf breakdown in the hyporheic zone

Particulate organic matter is the major source of energy for most low-order streams, but a large part of this litter is buried within bed sediment during floods and thus become poorly available for benthic food webs. The fate of this buried litter is little studied. In most cases, measures of breakdown rates consist of burying a known mass of litter within the stream sediment and following its breakdown over time. We tested this method using large litter bags (15 x 15 cm) and two field experiments. First, we used litter large bags filled with Alnus glutinosa leaves (buried at 20 cm depth with a shovel) in six stations within different land-use contexts and with different sediment grain sizes. Breakdown rates were surprisingly high (0.0011–0.0188 day-1) and neither correlate with most of the physico-chemical characteristics measured in the interstitial habitats nor with the land-use around the stream. In contrast, the rates were negatively correlated with a decrease in oxygen concentrations between surface and buried bags and positively correlated with both the percentage of coarse particles (20–40 mm) in the sediment and benthic macro-invertebrate richness. These results suggest that the vertical exchanges with surface water in the hyporheic zone play a crucial role in litter breakdown. Second, an experimental modification of local sediment (removing fine particles with a shovel to increase vertical exchanges) highlighted the influence of grain size on water and oxygen exchanges, but had no effect on hyporheic breakdown rates. Burying large litter bags within sediments may thus not be a relevant method, especially in clogged conditions, due to changes induced through the burial process in the vertical connectivity between surface and interstitial habitats that modify organic matter processing

Using Targeted Nano-Antibiotics to Improve Antibiotic Efficacy against Staphylococcus aureus Infections

International audienceThe poor bioavailability of antibiotics at infection sites is one of the leading causes of treatment failure and increased bacterial resistance. Therefore, developing novel, non-conventional antibiotic delivery strategies to deal with bacterial pathogens is essential. Here, we investigated the encapsulation of two fluoroquinolones, ciprofloxacin and levofloxacin, into polymer-based nanocarriers (nano-antibiotics), with the goal of increasing their local bioavailability at bacterial infection sites. The formulations were optimized to achieve maximal drug loading. The surfaces of nanoantibiotics were modified with anti-staphylococcal antibodies as ligand molecules to target S. aureus pathogens. The interaction of nano-antibiotics with the bacterial cells was investigated via fluorescent confocal microscopy. Conventional tests (MIC and MBC) were used to examine the antibacterial properties of nano-antibiotic formulations. Simultaneously, a bioluminescence assay model was employed, revealing the rapid and efficient assessment of the antibacterial potency of colloidal systems. In comparison to the free-form antibiotic, the targeted nano-antibiotic exhibited enhanced antimicrobial activity against both the planktonic and biofilm forms of S. aureus. Furthermore, our data suggested that the efficacy of a targeted nano-antibiotic treatment can be influenced by its antibiotic release profile

Hyaluronic Acid Functionalization with Jeffamine® M2005: A Comparison of the Thermo-Responsiveness Properties of the Hydrogel Obtained through Two Different Synthesis Routes

International audienceHyaluronic acid (HA) of different molar masses (respectively 38,000, 140,000 and 1,200,000 g.mol−1) have been functionalized with a commercial poly(etheramine), Jeffamine® M2005, in order to devise physical thermo-responsive hydrogels. Two routes have been studied, involving the use of either water for the first one or of N,N′-Dimethylformamide (DMF), a polar aprotic solvent, for the second one. In the case of the water route, the reaction was performed using a mixture of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling reagents. The reaction was optimized while making sure no free M2005 remained in the final material, leading to M2005 grafting degrees of about 4%, which enabled the formation of hydrogels by increasing the temperature. In the case of the organic solvent route, propylphosphonic anhydride T3P® was used as a coupling reagent in DMF, resulting in a M2005 grafting degree of around 8% with better thermo-responsive properties of HA-g-M2005 compared to those obtained when the reaction was performed in water. However, the reaction systematically led to covalent cross-linking in the case of the HA, with the highest starting molar masses resulting in a very different rheological behaviour and with higher gel strength retaining thermo-responsive behaviour but being only poorly soluble in water

Hydrogels Based on Polysaccharides Grafted Ferulic Acid: A Biomimetic Approach

International audienc

Polyelectrolyte complexes of hyaluronic acid and diethylaminoethyl dextran: Formation, stability and hydrophobicity

International audienc

Thermoresponsive nanogels based on polyelectrolyte complexes between polycations and functionalized hyaluronic acid

International audienc

Application of Polymeric Nanocarriers for Enhancing the Bioavailability of Antibiotics at the Target Site and Overcoming Antimicrobial Resistance

International audienceAntimicrobial resistance is one of the greatest threats to global health. Although the efforts in antibiotic drug discovery continue to play a pivotal role, this solution alone probably will not be enough to ensure the required level of infection control in the future. New strategies and innovative modes of action are desperately needed to preserve the effectiveness of antimicrobials. Accordingly, antibiotic delivery based on polymeric nanoparticles is one of the possible methods that has been recently explored to improve their pharmacokinetic profile. Through optimized access of antibiotics to their sites of action, nanocarriers can unlock the full potential of the antibiotic cargoes, extend the antimicrobial spectrum, and reduce the required dose of antibiotic while preserving efficacy. Additionally, the use of an antibiotic-loaded nanocarrier is also considered a steady solution as novel molecules can be continuously developed and incorporated into the delivery platform. This review describes the present state of polymeric nanocarriers in enhancing antibiotic treatment, including improved pharmacokinetic properties and restored antibiotic efficacy against drug-resistant bacteria. Additionally, the current challenges and the future direction of this field are discussed

Microgels Based on Carboxymethylpullulan Grafted with Ferulic Acid Obtained by Enzymatic Crosslinking in Emulsion for Drug Delivery Systems

International audienc

Curdlan microspheres. Synthesis, characterization and interaction with proteins (enzymes, vaccines)

International audienceMicroparticles of curdlan, synthesized through crosslinking with epichlorohydrin in organic suspension media, were chemically modified with the aim of introducing strongly and/or weakly acidic anionic and palmitoyl hydrophobic groups. Microparticles of both curdlan and curdlan derivatives were physico-chemically characterized. Study of the interaction with enzymes, such as lysozyme, and vaccines, such as tetanus anatoxin, showed a co-operative protein retention effect, induced by electrostatic and hydrophobic forces. The results of the in vitro release studies on support–protein complexes recommend them as potential controlled release systems

New Polysaccharide-based Microparticles Crosslinked with Siloxane: Interactions with Biologically Active Substances

International audienceThe interaction of microparticles of carboxymethyl pullulan crosslinked with siloxane (provided by a new crosslinking agent: 3-(glycid oxypropyl) trimethoxysilane) with biologically active molecules, such as enzymes (lysozyme) and drugs (propranolol, quinidine) was studied. The anionic amphiphilic supports retained through electrostatic and/or hydrophobic forces, variable amounts of the substances as a function of their structure, such as crosslinking degree and amount of uncrosslinked alkylsilane chains. The absorption of lysozyme on the supports followed the Langmuir isotherm, which allowed the calculation of constants k1 and k2. Both retention and in vitro release behavior of these support potential applications in controlled drug release as well as immobilization and purification of enzymes