No abstract

A region was identified on the methicillin resistance determinant (mec) isolated from Staphylococcus epidermidis and cloned into Staphylococcus carnosus which was responsible for a novel downregulation of the expression of methicillin resistance. The presence of this region reduced the overall expression of methicillin resistance and the synthesis of the mec-encoded penicillin-binding protein 2' (PBP 2') in S. carnosus. This region was located by Bal31 deletion mutagenesis upstream of the structural gene for PBP 2'. Deletions within this region resulted in higher levels of expression of methicillin resistance and increased levels of PBP 2' synthesis. We tentatively called this region mecR. Analysis of selected Mcr strains of Staphylococcus aureus and S. epidermidis by Southern hybridization suggested that the natural occurrence of two types of mec resistance determinants differ by the presence or absence of mecR-specific sequences.

A 6.2-kilobase chromosomal DNA fragment from a methicillin-resistant Staphylococcus epidermidis strain was cloned into Staphylococcus carnosus by using staphylococcal plasmid pCA44 as the vector. The recombinant plasmid obtained, pBBB21, conferred methicillin resistance on its host and was responsible for the synthesis of a low-affinity penicillin-binding protein (PBP), PBP 2'. PBP 2' determined by the S. epidermidis DNA and expressed as a membrane-bound PBP in S. carnosus reacted with monoclonal antibodies directed against PBP 2' of Staphylococcus aureus origin, and the cloned S. epidermidis DNA hybridized to the methicillin (mec)-specific DNA from S. aureus. These findings point to a common origin of the methicillin resistance determinant in staphylococci.

Ag-Ni/Cu alloys grown by electrodeposition in the organic solvent was been investigated. Know that phase diagram of Ag-Ni system is sample eutectic type with very small (<1wt%) mutual solubility and absence of intermediate compounds [1]. In our electrodeposition experiments single phase of solid solution Ag-Ni film alloys with any given compounds (10wt%Ag-90wt%Ni, 40wt%Ag-60wt%Ni, 70wt%Ag-30wt%Ni) are grown. Variations of alloy structure are possible by change of salts concentration in the solution and voltage between electrodes. Grain size was been determinate from broad of the x-ray diffraction pikes. For the different compounds the grain sizes are different (with 40-50 Å for alloys near 1:1 compound). Both Ag and Ni have bcc structures with very different parameters (15% difference). Unit cell parameters for intermediate alloys have volumes between unit cell parameters of the pour elements. Prepared mechanically alloying Ag50Ni50 is nanostructure of pour (Ag and Ni) elements [2]. Our electrodeposition Ag-Ni alloys produced the solid solution Ag-Ni alloys. We assume that growth of solid solutions compounds in Ag-Ni system by electrodeposition method is possible due the low (room) grown temperature.