Mechanistic Study of the Kinetic Phenomena Influencing the Bacteriostatic Action of Silver Ions in Agar Bioassays.

Bacteriostatic action of a biocidal agent results from the cumulative impact of different kinetics, including those of bacterial growth, mass transfer of the agent and its antibacterial action against the targeted bacteria. Current studies on bacteriostatic effects always directly consider the combination of these kinetics at given times, without discrimination between each other. This work introduces a novel approach, consisting of first studying independently, by the experiment and the model, the different kinetics involved, and then in coupling these kinetics to obtain a model that will be confronted with experimental data. An agar diffusion test with silver ions against Escherichia coli bacteria was implemented herein to assess the relevance of this approach. This work achieved to characterize the different kinetics and to propose a dynamic model combining them, which fits the experimental data with a silver diffusivity in the biofilm fixed to 7.0 ± 0.1 × 10-12 m2 s-1. This study also proves that the diffusive phenomenon was limiting the bacteriostatic action of silver ions over the test duration.

Anti-bacterial dynamic hydrogels prepared from O-carboxymethyl chitosan by dual imine bond crosslinking for biomedical applications.

Imine dynamic hydrogels are synthesized via dual-imine bond crosslinking from O-carboxymethyl chitosan (CMCS) and a water soluble dynamer using a 'green' approach. Three dynamers are prepared through reaction of benzene-1,3,5-tricarbaldehyde and di-amino Jeffamine with molar mass of 500, 800 and 1900, respectively. Hydrogels, namely H500, H800 and H1900 are then obtained by mixing CMCS and dynamer aqueous solutions. FT-IR confirms the formation of hydrogels via imine bonding. H1900 presents larger pore size and higher storage modulus as compared to H500 and H800 due to the higher molar mass of Jeffamine linker. The hydrogels exhibit pH sensitive swelling behavior due to electrostatic attraction or repulsion in the pH range from 3 to 10. The highest swelling ratio is obtained at pH 8, reaching 7500% for H800. Self-healing of hydrogels is evidenced by rheological measurements with alternatively applied low and high strains, and by using a macroscopic approach with re-integration of injected filaments. Furthermore, the H1900 membrane exhibits outstanding antibacterial activity against an E. coli suspension at 108 CFU mL-1. Therefore, dynamic hydrogels synthesized from CMCS and Jeffamine present outstanding rheological, swelling, self-healing and antibacterial properties, and are most promising as healthcare material in wound dressing, drug delivery and tissue engineering.

Uranium removal and microbial community in a H2-based membrane biofilm reactor.

We evaluated a hydrogen-based membrane biofilm reactor (MBfR) for its capacity to reduce and remove hexavalent uranium [U(VI)] from water. After a startup period that allowed slow-growing U(VI) reducers to form biofilms, the MBfR successfully achieved and maintained 94-95% U(VI) removal over 8 months when the U surface loading was 6-11 e(-) mEq/m(2)-day. The MBfR biofilm was capable of self-recovery after a disturbance due to oxygen exposure. Nanocrystalline UO2 aggregates and amorphous U precipitates were associated with vegetative cells and apparently mature spores that accumulated in the biofilm matrix. Despite inoculation with a concentrated suspension of Desulfovibrio vulgaris, this bacterium was not present in the U(VI)-reducing biofilm. Instead, the most abundant group in the biofilm community contained U(VI) reducers in the Rhodocyclaceae family when U(VI) was the only electron acceptor. When sulfate was present, the community dramatically shifted to the Clostridiaceae family, which included spores that were potentially involved in U(VI) reduction.