Temperature-regulated efflux pump/potassium antiporter system mediates resistance to cationic antimicrobial peptides in Yersinia

Most bacterial pathogens are resistant to cationic antimicrobial peptides (CAMPs) that are key components of the innate immunity of both vertebrates and invertebrates. In Gram-negative bacteria, the known CAMPs resistance mechanisms involve outer membrane (OM) modifications and specifically those in the lipopolysaccharide (LPS) molecule. Here we report, the characterization of a novel CAMPs resistance mechanism present in Yersinia that is dependent on an efflux pump/potassium antiporter system formed by the RosA and RosB proteins. The RosA/RosB system is activated by a temperature shift to 37 degrees C, but is also induced by the presence of the CAMPs, such as polymyxin B. This is the first report of a CAMPs resistance system that is induced by the presence of CAMPs. It is proposed that the RosA/RosB system protects the bacteria by both acidifying the cytoplasm to prevent the CAMPs action and pumping the CAMPs out of the cell.

Potassium canrenoate treatment in paediatric patients: a population pharmacokinetic study using novel dried blood spot sampling

Objective: To characterize the population pharmacokinetics of canrenone following administration of potassium canrenoate (K-canrenoate) in paediatric patients.

Methods: Data were collected prospectively from 37 paediatric patients (median weight 2.9?kg, age range 2 days–0.85 years) who received intravenous K-canrenoate for management of retained fluids, for example in heart failure and chronic lung disease. Dried blood spot (DBS) samples (n?=?213) from these were analysed for canrenone content and the data subjected to pharmacokinetic analysis using nonlinear mixed-effects modelling. Another group of patients (n?=?16) who had 71 matching plasma and DBS samples was analysed separately to compare canrenone pharmacokinetic parameters obtained using the two different matrices.

Results: A one-compartment model best described the DBS data. Significant covariates were weight, postmenstrual age (PMA) and gestational age. The final population models for canrenone clearance (CL/F) and volume of distribution (V/F) in DBS were CL/F (l/h)?=?12.86?×? (WT/70.0)0.75?×?e [0.066?×? (PMA?-?40]) and V/F (l)?=?603.30?×? (WT/70)?×?(GA/40)1.89 where weight is in kilograms. The corresponding values of CL/F and V/F in a patient with a median weight of 2.9?kg are 1.11?l/h and 20.48?l, respectively. Estimated half-life of canrenone based on DBS concentrations was similar to that based on matched plasma concentrations (19.99 and 19.37?h, respectively, in 70?kg patient).

Conclusion: The range of estimated CL/F in DBS for the study population was 0.12–9.62?l/h; hence, bodyweight-based dosage adjustment of K-canrenoate appears necessary. However, a dosing scheme that takes into consideration both weight and age (PMA/gestational age) of paediatric patients seems more appropriate.

Development of a heterogeneous catalyst for lignocellulosic biomass conversion:Glucose dehydration by metal chlorides in a silica-supported ionic liquid layer

An attempt is made to immobilize the homogeneous metal chloride/EMIMCl catalyst for glucose dehydration to 5-hydroxymethylfurfural. To this end, ionic liquid fragments were grafted to the surface of SBA-15 to generate a heterogenized mimick of the homogeneous reaction medium. Despite a decrease in the surface area, the ordered mesoporous structure of SBA-15 was largely retained. Metal chlorides dispersed in such ionic liquid film are able to convert glucose to HMF with much higher yields as is possible in the aqueous phase. The reactivity order CrCl > AlCl > CuCl > FeCl is similar to the order in the ionic liquid solvent, yet the selectivity are lower. The HMF yield of the most promising CrCl-Im-SBA-15 can be improved by using a HO:DMSO mixture as the reaction medium and a 2-butanol/MIBK extraction layer. Different attempts to decrease metal chloride leaching by using different solvents are described. © 2013 American Institute of Chemical Engineers Environ Prog.

Potassium-doped Ni-MgO-ZrO catalysts for dry reforming of methane to synthesis gas

Ni/K-MgO-ZrO catalysts for dry reforming of methane, with a range of Mg/Zr ratios and each containing about 10 wt% Ni, were prepared via Ni nitrate impregnation on MgO-ZrO supports synthesized by co-precipitation using KCO. It was found that a proportion of the potassium of the precipitant remained in the samples and improved the stability of the catalysts in the reaction. It was also shown that reduction of the catalysts at 1,023 K without calcination in air is necessary for stable and high activity; calcination in air at 1,073 K gives a deterioration of the catalytic properties, leading to rapid deactivation during the reaction. The order of the CH conversions of the reduced catalysts after 14 h on stream was as follows: Ni/K-MgZr ~ Ni/K-Mg ≥ Ni/K-MgZr Ni/K-Zr. A catalyst with 0.95 wt% K on MgO-ZrO with a Mg:Zr mole ratio of 5:2 showed the best resistance to deactivation. Experiments in a microbalance system showed that there was only negligible coke deposition on the surface of this sample. This behaviour was attributed to the presence of Ni nanoparticles with a diameter of less than 10 nm located on a MgO/NiO solid solution shell doped by K ions; this in turn covers a core of tetragonal ZrO and/or a MgO/ZrO solid solution. This conclusion was supported by EDS/TEM, XPS, XRD and H chemisorption measurements. © 2013 Springer Science+Business Media New York.

FRENKEL-KONTOROVA DOMAIN-WALL PHASE-TRANSITIONS IN AN ADSORBED LAYER - POTASSIUM ON CO(10(1)OVER-BAR-0)

As the potassium fractional coverage of a cobalt {1010BAR} surface is increased over the range 0.2 to 0.6 monolayer the adlayer passes through a series of phase transitions. A commensurate phase is formed at exactly 0.5 monolayer, and corresponds to adatoms bonded in high-symmetry hollow sites on the unreconstructed cobalt surface, with an effective adatom radius lying between the ionic and covalent radii of potassium. A detailed structural study shows that the structural transitions can be characterised within a one-dimensional Frenkel-Kontorova model, with small lateral displacements of adatoms away from hollow sites in the low and high coverage phases. The low coverage phases progress from a distributed vacancy structure to a low density domain-wall structure; while the high coverage phase formed above half a monolayer is a high density asymmetric domain-wall structure.

THE SURFACE-STRUCTURE OF A C(2 X-2) POTASSIUM OVERLAYER ON CO(1010)

The surface structure of the clean Co{1010BAR} surface and a c(2 x 2) potassium overlayer have been determined by quantitative low energy electron diffraction. The Co{1010BAR} sample has been shown to be laterally unreconstructed with the surface being uniquely terminated by an outermost closely packed double layer (dz12 = 0.68 angstrom). A damped oscillatory relaxation of the outermost three atomic layers occurs, with relaxations DELTA-dz12 = -6.5 +/- 2% and DELTA-dz23 = +1.0 +/- 2%.

The c(2 x 2) overlayer formed at a coverage of 0.5 ML was subjected to a full I-V analysis. A range of adsorption sites were tested including fourfold hollow, on-top, and both long and short bridge sites in combination with both "long" and "short" cobalt interlayer terminations. A clear preference was found for adsorption in the maximal coordination fourfold hollow site. No switching of surface termination occurs. The potassium adatoms reside in the [1210BAR] surface channels directly above second layer cobalt atoms with a potassium to outermost cobalt interlayer separation of 2.44 +/- 0.05 angstrom. Potassium-cobalt bond lengths of 3.40 +/- 0.05 and 3.12 +/- 0.05 angstrom between the four (one) outermost (second) layer nearest-neighbour substrate atoms suggests a potassium effective radius of 1.87 +/- 0.05 angstrom, somewhat smaller than the Pauling covalent radius and considerably larger than the ionic radius (1.38 angstrom). The alkali-surface bonding is thus predominantly "covalent"/"metallic".