Effect of simulated microgravity on the virulence properties of the opportunistic bacterial pathogen Staphylococcus aureus

Extended manned space flight will result in a diminution of immune status and cause profound changes in the human bacterial microbiota, leading to increased risk of infection. Experiments conducted during short-term flight suggest that growth in microgravity leads to increases in bacterial antibiotic resistance and to cell wall changes. Growth under low-shear modelled microgravity (LSMMG) indicated that a reduced gravitational field acts as an environmental signal for expression of enhanced bacterial virulence in Gram-negative pathogens. We examined the effect of simulated microgravity on parameters of virulence in clinical isolates of Staphylococcus aureus. Three strains were grown under LSMMG in a High Aspect Ratio Vessel and compared with cells grown under normal gravity (NG) in the same vessel. There were no significant differences in the antibiotic susceptibility, growth rate or morphology of staphylococci grown under LSMMG compared to NG. LSMMG-induced reductions in synthesis of the pigment staphyloxanthin were noted. Strains secreted less protein under LSMMG and reductions in haemolysin secretion were found. Reduced expression of the major virulence determinant "-toxin in the microgravity environment was found by gene amplification. Thus, in contrast to published data on Gram-negative pathogens, simulated microgravity reduces the expression of key virulence determinants of S. aureus

Non-stoichiometry defects and radiation hardness of lead tungstate crystals PbWO4

It has been stated many times that the formation of radiation infringements in PbWO4 is to a big extent stipulated by the non-stoichiometry defects of the crystals, arising in the process of their growth and annealing. To refine the idea of characteristics of the non-stoichiometry defects and their effect on the radiation hardness of PbWO4, the current study is aimed at the melt composition infringements during its evaporation and at optical transmission of crystals obtained in these conditions after their irradiation ((CS)-C-137 source). In the optical transmission measurements along with traditional techniques a method "in situ" was used, which provided the measurements in fixed points of the spectrum (380, 470 and 535nm) directly in the process of the irradiation. X-ray phase and fluorescence analysis of condensation products of vapours over PbWO4 melt has found PbWO4 phase in their content as well as compounds rich in lead PbO, Pb2WO5 with overall ratio Pb/W (3.2). Correspondingly, the lack of lead and variations in the content of oxygen are pointed out as the major growth defects of nonstoichiometry of PbWO4 crystals. The oxygen variations are determined by the partial oxygen pressure in the atmosphere of growth or annealing of the crystals. The obtained results were compared with known conceptions of PbWO4 crystal colour centres. The possibilities of the formation of these centres accounting for the discovered loss of lead and oxygen exchange between the external medium and the crystal were considered. (C) 2002 Elsevier Science B.V. All rights reserved

Iron-related luminescence centers in ZnWO4 : Fe

A systematic spectroscopic study of single ZnWO4 :Fe crystals with different iron concentrations has been performed under excitation by ultraviolet light, by synchrotron radiation or under photostimulation by near-infrared light. The luminescence of Fe3+-related centres has been studied. It is shown that iron centres of different types efficiently promote the formation of crystal defects at low temperatures. Electrons and holes can be trapped near Fe2+ or Fe3+ ions, which is further revealed in phosphorescence, thermostimulated or photostimulated luminescence. At room temperature the main effect of iron impurity is to reduce the light yield of a ZnWO4 scintillator