Novel Klebsiella pneumoniae K23-Specific Bacteriophages From Different Families: Similarity of Depolymerases and Their Therapeutic Potential.

Antibiotic resistance is a major public health concern in many countries worldwide. The rapid spread of multidrug-resistant (MDR) bacteria is the main driving force for the development of novel non-antibiotic antimicrobials as a therapeutic alternative. Here, we isolated and characterized three virulent bacteriophages that specifically infect and lyse MDR Klebsiella pneumoniae with K23 capsule type. The phages belonged to the Autographiviridae (vB_KpnP_Dlv622) and Myoviridae (vB_KpnM_Seu621, KpS8) families and contained highly similar receptor-binding proteins (RBPs) with polysaccharide depolymerase enzymatic activity. Based on phylogenetic analysis, a similar pattern was also noted for five other groups of depolymerases, specific against capsule types K1, K30/K69, K57, K63, and KN2. The resulting recombinant depolymerases Dep622 (phage vB_KpnP_Dlv622) and DepS8 (phage KpS8) demonstrated narrow specificity against K. pneumoniae with capsule type K23 and were able to protect Galleria mellonella larvae in a model infection with a K. pneumoniae multidrug-resistant strain. These findings expand our knowledge of the diversity of phage depolymerases and provide further evidence that bacteriophages and phage polysaccharide depolymerases represent a promising tool for antimicrobial therapy.

Experimental demonstration of the feasibility of laser communication with reentry spacecraft at 1.55 µm.

It has been demonstrated experimentally for the first time, to the best of our knowledge, that reliable laser communication at 1.55 µm can be established with reentry spacecraft across the entire atmospheric descent trajectory as a way to avoid radio blackout. A plasma sheath with parameters similar to those around the spacecraft is reproduced at the Lomonosov Moscow State University Mechanics Institute Shock Tube Facility. Our experiments validate that the currently existing, high-maturity-level, free-space laser communication technology can provide real-world laser link implementation with the descending spacecraft.

Si3N4-TiN nanocomposite by nitration of TiSi2 and consolidation by hot pressing and spark plasma sintering.

Homogeneous nanostructured Si3N4-TiN composite powder was obtained by nitration of a TiSi2 powder precursor in a nitrogen flow. Mechanoactivation of titanium disilicide increases the nitration rate and reduces the temperature of formation of the Si3N4 and TiN. The properties of hot pressing (HP) and spark plasma sintering (SPS) of the nanostructured Si3N4-TiN composite with Y2O3 and Al2O3 additives have been studied. In the case of the HP-prepared composite the processing conditions are sufficient to form a stable, equilibrated grain boundary framework. The SPS consolidation is extremely rapid, low-temperature process and the sintering temperature was 300-400 degrees C lower than that of the hot pressing temperature. As a result the grain boundary framework was underdeveloped. Post-sintering anneal of the SPS-prepared samples caused significant improvement of their mechanical properties. The SPS and HP-derived Si3N4-40 mass% TiN-6 mass% Y2O3-2 mass% Al2O3 nano-composite of 98.4% and 98.9% of relative density demonstrate the Vickers hardness values of 13.2 and 13.7 GPa, respectively. The grains of Si3N4 and TiN were much finer in the case of the SPS-derived ceramic composite. However, the better development of the grain boundary framework in the case of the higher temperature HP treatment in comparison to the SPS significantly reduced the advantage of nanocrystallinity. In both cases the fracture toughness was comparable even after the improvement of grain boundary framework during the SPS consolidation. The K(1c), of 7.83 MPax m(1/2) of the sample prepared according to the best SPS regime is also comparable to K(1c) of 8.30 MPa x m(1/2) of much coarser hot pressed ceramic with very similar relative density.