In vitro interaction between ceftazidime and vancomycin/teicoplanin in the presence of azithromycin against Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen, intrinsically resistant to many antibiotics and prone to acquire resistance against many drugs. It is assumed that agents that disorganise the structure of the outer membrane might allow the passage of other drugs into cell. To verify this hypothesis, ceftazidime (CAZ) has been tested in association with glycopeptides (GLYs) and azithromycin (AZI). Time-kill experiments were performed on a representative strain. CAZ in combination with GLYs showed 99, 90 and 10% of CFU/ml reduction in 33.9,52.5 and 13.6% of the cases, respectively; the addition of AZI increased the incidence of 99% CFU/ml reduction to 42% of the cases. Indifference was the most common finding, and additive/synergism in the other cases. Present findings demonstrated that CAZ favourably reacted with GLYs in the presence of AZI

Magnetic properties of spin diluted iron pnictides from muSR and NMR in LaFe1-xRuxAsO

The effect of isoelectronic substitutions on the microscopic properties of LaFe1-xRuxAsO, for 0< x< 0.8, has been investigated by means of muSR and 139La NMR. It was found that Ru substitution causes a progressive reduction of the N\`eel temperature (T_N) and of the magnetic order parameter without leading to the onset of superconductivity. The temperature dependence of 139La nuclear spin-lattice relaxation rate 1/T_1 can be suitably described within a two-band model. One band giving rise to the spin density wave ground-state, while the other one is characterized by weakly correlated electrons. Fe for Ru substitution yields to a progressive decrease of the density of states at the Fermi level close to the one derived from band structure calculations. The reduction of T_N with doping follows the predictions of the J_1-J_2 model on a square lattice, which appears to be an effective framework to describe the magnetic properties of the spin density wave ground-state.Comment: 6 pages, 8 figure

Validation of a Simulation Methodology for Thermoplastic and Thermosetting Composite Materials Considering the Effect of Forming Process on the Structural Performance

This research work investigated the influence of the press molding manufacturing process on the mechanical properties, both for thermoplastic and thermosetting fiber reinforced composite materials. The particular geometry of the case study, called Double Dome, was considered in order to verify the behavior of the Thermoplastic and Thermosetting prepreg in terms of shell thickness variation and fibers shear angle evolution during the thermoforming process. The thermoforming simulation was performed using LS-DYNA Finite Element Analysis (FEA) code, and the results were transferred by Envyo, a dedicated mapping tool, into a LS-DYNA virtual model for the structural simulation. A series of Double Dome specimens was produced with industrial equipment, and a bending experimental test was been carried on. Finally, a numerical-experimental correlation was performed, highlighting a significant forecast of the mechanical properties for the considered component

Evaluation of post-antibiotic effect in Gram-negative and Gram-positive bacteria

Although the postantibiotic effect (PAE) is a well recognized phenomenon, the mechanism by which it is induced has not fully elucidated yet. It has been suggested that PAE is the time required by bacteria to synthesize proteins or mRNA characterized by a short half-life that are consumed during antibiotic treatment.This phenomenon is widely studied on Gram-positive cocci and Gram-negative rods, while information about Gram-positive rods and Gram-negative cocci are scanty.To gain new insights on the PAE, this study was addressed to evaluated the time required by Moraxella catarrhalis and Lactobacillus planctarum to resume their physiological growth rate after exposure to various antibiotics. Methods PAE was estimated in accordance with the method of Craig and Gudmundsson using the following drugs: penicillin, piperacillin-tazobactam, cefalotin, ceftazidime, imipenem, ciprofloxacin, gentamycin and azithromycin. Log-phase bacteria were exposed to drug at a concentration corresponding to 4 times the MIC value for 1h.The drug was inactivated by 1:1000 dilution. Bacterial counts were determined at time zero, immediately after drug dilution, and at each hour after removal for 6 - 7h by a pour-plate technique. The PAE was defined as the difference in time required by test and control cultures to increase by 1 log in CFU number. Results All drugs tested induced a PAE on the strains studied. M. catarrhalis registered PAE values ranging between 0,5 (gentamycin) and 2 (ceftazidime, imipenem and azithromycin).With respect to L. plantarum a PAE between 0,8 (cefalotin) and 3 hours (ciprofloxacin) were detected. Conclusion. These findings demonstrated that all the drugs tested were able to induce a PAE on the strains tested.This observation differs from that observed on Gram-negative rods characterised by negative PAE values induced by penicillins and cephalosporins.This results might reflect the different target of these compounds on these Gram-positive rods or the different affinity of the antibiotics to several PBPs that required more time to restore the physiological fitness of the bacterial cell

Temperature dependent local atomic displacements in Ru substituted SmFe1?xRuxAsO0.85F0.15superconductors

The local structure of SmFe1-xRuxAsO0.F-85(0.15) (x = 0.0, 0.05, 0.25 and 0.5) superconductors has been investigated by temperature dependent As K-edge extended x-ray absorption fine structure analysis. The effect of Ru substitution remains confined to the iron-arsenide layer but neither the static disorder nor the Fe-As bond strength suffers any change for x <= 0.25. With further Ru substitution the static disorder increases while the Fe-As bond strength remains unchanged. Also, the Ru-As distance (similar to 2.42 angstrom), different from the Fe-As distance (similar to 2.39 angstrom), does not show any change in its force constant with Ru substitution. These observations suggest that the SmFe1-xRuxAsO0.F-85(0).(15) system breaks down into coexisting local electronic phases on isoelectric substitution in the active FeAs layer

Theoretical and experimental investigation of magnetotransport in iron chalcogenides

We explore the electronic, transport and thermoelectric properties of Fe1+ySexTe1-x compounds to clarify the mechanisms of superconductivity in Fe-based compounds. We carry out first-principles density functional theory (DFT) calculations of structural, electronic, magnetic and transport properties and measure resistivity, Hall resistance and Seebeck effect curves. All the transport properties exhibit signatures of the structural/magnetic transitions, such as discontinuities and sign changes of the Seebeck coefficient and of the Hall resistance. These features are reproduced by calculations provided that antiferromagnetic correlations are taken into account and experimental values of lattice constants are considered in DFT calculations. On the other hand, the temperature dependences of the transport properties can not be fully reproduced, and to improve the agreement between experiment and DFT calculations it is necessary to go beyond the constant relaxation time approximation and take into account correlation effects

75As NQR signature of the isoelectronic nature of ruthenium for iron substitution in LaFe1-xRuxAsO

We have investigated the effects of the isovalent ruthenium substitution in LaFe1−xRuxAsO, by extensive 75As NQR (nuclear quadrupole resonance) measurements, supported by DFT (density functional theory) calculations, in order to characterize both the lattice and electronic structure details. The evidence for five different local configurations around the arsenic site emerges upon increasing ruthenium for iron substitution. DFT calculations confirm the attribution of the measured electric field gradients (EFGs) to ruthenium atom occupancies (0, 1, 2, 3, and 4) on the nearest-neighbour sites of arsenic. It is found that the low-frequency (Ru-free) NQR peak remains almost unaffected upon ruthenium substitution, providing an experimental confirmation that ruthenium does not introduce delocalized carriers in the iron plane