Corrosion Resistance of MgZn Alloy Covered by Chitosan-Based Coatings.

Chitosan coatings are deposited on the surface of Mg20Zn magnesium alloy by means of the spin coating technique. Their structure was investigated using Fourier Transform Infrared Spectroscopy (FTIR) an X-ray photoelectron spectroscopy (XPS). The surface morphology of the magnesium alloy substrate and chitosan coatings was determined using Scanning Electron Microscope (FE-SEM) analysis. Corrosion tests (linear sweep voltamperometry and chronoamperometry) were performed on uncoated and coated magnesium alloy in the Hank's solution. In both cases, the hydrogen evolution method was used to calculate the corrosion rate after 7-days immersion in the Hank's solution at 37 °C. It was found that the corrosion rate is 3.2 mm/year and 1.2 mm/year for uncoated and coated substrates, respectively. High corrosion resistance of Mg20Zn alloy covered by multilayer coating (CaP coating + chitosan water glass) is caused by formation of CaSiO3 and Ca3(PO4)2 compounds on its surface.

Determination of Contact Resistance of Thermal Interface Materials Used in Thermal Monitoring Systems of Electric Vehicle Charging Inlets.

The rapid growth of the electric vehicle (EV) market is observed. This is challenging from a materials point of view when it comes to the thermal monitoring systems of charging inlets, for which requirements are very restrictive. Because the thermal conductivity of the thermal interface material is usually measured, there is a significant research gap on the contact thermal resistance of novel materials used in the electric vehicle industry. Moreover, researchers mainly focus on electrically conductive materials, while for thermal monitoring systems, the most important requirement is a high dielectric breakdown voltage. In this paper, the thermal contact resistance of materials for EV applications was thoroughly analyzed. This study consisted of experimental measurements with the Laser Flash Analysis (LFA) method, as well as a theoretical analysis of thermal contact resistance. The main focus was on the extraction of contact and material thermal resistance. The obtained results have great potential to be used as input data for further numerical modeling of solutions that meet strict thermal accuracy requirements. Additionally, the chemical composition and internal structure were analyzed using scanning electron microscopy, to better describe the material.

Influence of High-Pressure Die Casting Parameters on the Cooling Rate and the Structure of EN-AC 46000 Alloy.

The paper presents the results of the research on the impact of process parameters of high-pressure, cold-chamber die casting of an industrial casting made of aluminium alloy on the casting properties assessed macroscopically by measuring the casting average density and microscopically through the characteristics of the casting microstructure. The analysis covers the influence of three selected velocity settings of the pressing plunger, which determine the filling time, and three values of the compression pressure setting characteristic of the third phase of the casting process. The cooling and solidification simulations of the casting were performed using the ProCAST software. During the simulation tests, the impact of the filling rate of the alloy into the die cavity on the cooling rate and the alloy solidification path at selected points were determined. The conducted research allowed linking the process parameters with the parameters of the casting structure with different wall thicknesses. Metallographic examinations of the castings were carried out using a light microscopy, SEM, and EDS analysis. The fraction of the phases α(Al), the size of dendritic cells, and the size of silicon particles, in the cross-sections of the castings with wall thickness of 3, 6, and 11 mm, respectively, were determined.

Perceiving space and optical cues via a visuo-tactile sensory substitution system: a methodological approach for training of blind subjects for navigation.

A methodological approach to perceptual learning was used to allow both early blind subjects (experimental group) and blindfolded sighted subjects (control group) to experience optical information and spatial phenomena, on the basis of visuo-tactile information transmitted by a 64-taxel pneumatic sensory substitution device. The learning process allowed the subjects to develop abilities in spatial localisation, shape recognition (with generalisation to different points of view), and monocular depth cue interpretation. During the training phase, early blind people initially experienced more difficulties than blindfolded sighted subjects (having previous perceptual experience of perspective) with interpreting and using monocular depth cues. The amelioration of the performance for all blind subjects during training sessions and the quite similar level of performance reached by two groups in the final navigation tasks suggested that early blind people were able to develop and apply cognitive understanding of depth cues. Both groups showed generalisation of the learning from the initial phases to cue identification in the maze, and subjectively experienced shapes facing them. Subjects' performance depended not only on their perceptual experience but also on their previous spatial competencies.

The Shigella OspC3 effector inhibits caspase-4, antagonizes inflammatory cell death, and promotes epithelial infection.

Caspase-mediated inflammatory cell death acts as an intrinsic defense mechanism against infection. Bacterial pathogens deploy countermeasures against inflammatory cell death, but the mechanisms by which they do this remain largely unclear. In a screen for Shigella flexneri effectors that regulate cell death during infection, we discovered that Shigella infection induced acute inflammatory, caspase-4-dependent epithelial cell death, which is counteracted by the bacterial OspC3 effector. OspC3 interacts with the caspase-4-p19 subunit and inhibits its activation by preventing caspase-4-p19 and caspase-4-p10 heterodimerization by depositing the conserved OspC3 X1-Y-X2-D-X3 motif at the putative catalytic pocket of caspase-4. Infection of guinea pigs with a Shigella ospC3-deficient mutant resulted in enhanced inflammatory cell death and associated symptoms, correlating with decreased bacterial burdens. Salmonella Typhimurium and enteropathogenic Escherichia coli infection also induced caspase-4-dependent epithelial death. These findings highlight the importance of caspase-4-dependent innate immune responses and demonstrate that Shigella delivers a caspase-4-specific inhibitor to delay epithelial cell death and promote infection.

A Tecpr1-dependent selective autophagy pathway targets bacterial pathogens.

Selective autophagy of bacterial pathogens represents a host innate immune mechanism. Selective autophagy has been characterized on the basis of distinct cargo receptors but the mechanisms by which different cargo receptors are targeted for autophagic degradation remain unclear. In this study we identified a highly conserved Tectonin domain-containing protein, Tecpr1, as an Atg5 binding partner that colocalized with Atg5 at Shigella-containing phagophores. Tecpr1 activity is necessary for efficient autophagic targeting of bacteria, but has no effect on rapamycin- or starvation-induced canonical autophagy. Tecpr1 interacts with WIPI-2, a yeast Atg18 homolog and PI(3)P-interacting protein required for phagophore formation, and they colocalize to phagophores. Although Tecpr1-deficient mice appear normal, Tecpr1-deficient MEFs were defective for selective autophagy and supported increased intracellular multiplication of Shigella. Further, depolarized mitochondria and misfolded protein aggregates accumulated in the Tecpr1-knockout MEFs. Thus, we identify a Tecpr1-dependent pathway as important in targeting bacterial pathogens for selective autophagy.

The effect of an antibiotic policy on the control of vancomycin-resistant enterococci outbreak and on the resistance patterns of bacteria isolated from the blood of patients in a hematology unit.

INTRODUCTION: Antibiotic resistance has become one of the main medical problems worldwide. This is mainly due to an overuse and misuse of antibiotics. OBJECTIVES: The aim of the study was to assess the effect of an antibiotic policy and enhanced infection control on the occurrence of epidemic strains of vancomycin-resistant enterococci (VRE) and resistance patterns of bacteria isolated from the blood of patients hospitalized in two departments of a hematology center in Poland. PATIENTS AND METHODS: Antibiotic use was calculated in daily defined doses (DDD) per 100 patient-days during the two 5-month periods, before and after the introduction of the policy. Infection control measures included a 1-week screening for VRE rectal carriage and contact isolation. RESULTS: Antibiotic consumption decreased from 82.1 to 57.3 DDD per 100 patient-days, mainly because of a decrease in the use of co-trimoxazole, other antimicrobials active against anaerobes, and cephalosporins. A significant change in antibiotic resistance patterns was observed and in vitro efficacy of antibiotics against bacteria isolated from the blood increased remarkably. We managed to eradicate the outbreak of VRE. CONCLUSIONS: The introduction of antibiotic policy and enhanced infection control measures may prove efficacious in VRE control.

Clonal structure of Enterococcus faecalis isolated from Polish hospitals: characterization of epidemic clones.

To study the population structure of Enterococcus faecalis from Polish hospitals, 291 isolates were typed by pulsed-field gel electrophoresis and a novel multilocus sequence typing scheme (P. Ruiz-Garbajosa et al., J. Clin. Microbiol. 44:2220-2228, 2006). The isolates originated from geographically widespread medical institutions and were recovered during a 10-year period (1996 to 2005) from different clinical sources. The analysis grouped the isolates into five epidemic and 71 sporadic clones. The importance of the previously identified global clonal complexes CC2 and CC9 was corroborated by our findings that two of the Polish epidemic clones, A and J, were classified into these clonal complexes (CCs). However, the two most predominant clones, C (ST40) and F (CC87), did not cluster in the aforementioned CCs and may represent novel epidemic CCs. These clones may have emerged in Central Europe. Clone F, carrying glycopeptide resistance determinants of VanA or VanB phenotypes, caused several outbreaks in hematology units and appeared to be the most prevalent clone in recent years in Poland. Antimicrobial susceptibility testing and additional tests for pathogenicity-related phenotypes (hemolysin and gelatinase production) and genes (asa1 and esp) were performed to further characterize these epidemic clones. Multidrug resistance, glycopeptide resistance, presence of asa1, and production of hemolysin appeared to be statistically significant features related to epidemicity. Production of gelatinase was significant for two of the epidemic clones, whereas presence of the esp gene was not specific for the epidemic clones.

Molecular diversity of a putative virulence factor: purification and characterization of isoforms of an extracellular serine glutamyl endopeptidase of Enterococcus faecalis with different enzymatic activities.

A previously identified gene sprE of Enterococcus faecalis strain OG1 was shown to encode an extracellular serine protease that appears to belong to the glutamyl endopeptidase I staphylococcal group. A single form of SprE with a molecular mass of 25 kDa and a pH optimum between 7.0 and 7.5 was isolated from culture supernatant of wild-type E. faecalis strain OG1RF (TX4002); this form was apparently generated by cleavage of the Ser-1-Leu1 and Arg230-Leu231 peptide bonds of the secreted zymogen. In contrast, the culture supernatant of the gelatinase-null mutant, TX5264, with a nonpolar deletion of gelE which encodes the E. faecalis gelatinase, was found to contain several forms of SprE proteolytically processed on both the N and C termini; in addition to a full-length zymogen and a truncated zymogen, three mature forms of the SprE proteinase, Leu1-Ala237, Ser-1-Glu227, and Leu1-Glu227, were identified. As with the V8 proteinase of Staphylococcus aureus, the closest homologue of SprE, all of the active forms cleaved specifically Glu-Xaa peptide bonds but with substantially different efficiencies, while none was able to hydrolyze peptide bonds with Asp in the P1 position. The most active of all these enzyme forms against several substrates, including human fibrinogen and beta-chain insulin, was the Ser-1-Glu227 (-1S-SprE) isolated from TX5264; -1S-SprE, in contrast to other forms of SprE, was unstable at 37 degrees C, apparently due to autodegradation. In conclusion, our results demonstrate that sprE encodes a highly specific serine-type glutamyl endopeptidase, the maturation of which is dependent on the presence of gelatinase. In the absence of gelatinase activity, the aberrant processing of pro-SprE results in the appearance of a "superactive" form of the enzyme, -1S-SprE.

An Enterococcus faecium secreted antigen, SagA, exhibits broad-spectrum binding to extracellular matrix proteins and appears essential for E. faecium growth.

A gene encoding a major secreted antigen, SagA, was identified in Enterococcus faecium by screening an E. faecium genomic expression library with sera from patients with E. faecium-associated endocarditis. Recombinant SagA protein showed broad-spectrum binding to extracellular matrix (ECM) proteins, including fibrinogen, collagen type I, collagen type IV, fibronectin, and laminin. A fibrinogen-binding protein, purified from culture supernatants of an E. faecium clinical isolate, was found to match the N-terminal sequence of the predicted SagA protein and to react with the anti-SagA antibody, confirming that it was the SagA protein; this protein appeared as an 80- to 90-kDa smear on a Western blot that was sensitive to proteinase K and resistant to periodate treatment and glycoprotein staining. When overexpressed in E. faecium and Escherichia coli, the native and recombinant SagA proteins formed stable oligomers, apparently via their C-terminal domains. The SagA protein is composed of three domains: (i) a putative coiled-coil N-terminal domain that shows homology to the N-terminal domain of Streptococcus mutans SagA protein (42% similarity), previously shown to be involved in cell wall integrity and cell shape maintenance, and to the P45 protein of Listeria monocytogenes (41% similarity); (ii) a central domain containing direct repeats; and (iii) a C-terminal domain that is similar to that found in various proteins, including P45 (50% similarity) and P60 (52% similarity) of L. monocytogenes. The P45 and P60 proteins both have cell wall hydrolase activity, and the latter has also been shown to be involved in virulence, whereas cell wall hydrolase activity was not detected for SagA protein. The E. faecium sagA gene, like the S. mutans homologue, is located in a cluster of genes encoding proteins that appear to be involved in cell wall metabolism and could not be disrupted unless it was first transcomplemented, suggesting that the sagA gene is essential for E. faecium growth and may be involved in cell wall metabolism. In conclusion, the extracelluar E. faecium SagA protein is apparently essential for growth, shows broad-spectrum binding to ECM proteins, forms oligomers, and is antigenic during infection.