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The problem of formation and spread of S.aureus isolates with reduced sensitivity to vancomycin (Vancomycin intermediate S.aureus, VISA) limits the use of this antibiotic for the treatment of infections caused by MRSA. The formation of such a phenotype is complex and is associated with the accumulation of mutations in the genes involved in the biosynthesis of the cell wall. Genomic sequencing of seven isolates with different sensitivity to vancomycin and belonging to the same genetic line was carried out in the study: ST8 - t008 - SCCmec IVc. PAP analysis of isolates with reduced sensitivity to vancomycin did not reveal hVISA/VISA phenotypes, while PAP/AUC was 0.53-0.7. Comparison of 83% of the core parts of isolates’ genomes with MIC = 1 mg/ml and 2 mg/ml, as well as control genomes (NCBI GenBank) with known sensitivity, revealed different clustering, the isolates with MIC=2 mg/ml were localized in one cluster. Comparison of the nucleotide concatenate composed of 44 genes involved in the assembly of the cell wall also showed that the isolates were assembled into one cluster. Unique mutations were identified for isolates with MIC=2 mg/ml in murZ (T353A), rpoB (Y946C), and fdh2 (G446S). Thus, isolates with reduced sensitivity to vancomycin did not have the hVISA or VISA phenotype. However, the identified mutations in the «key» genes of peptidoglycan biosynthesis may indicate the initial stage of selection of resistance to vancomycin with the formation of pre-hVISA.

Ceftaroline is a unique cephalosporin with activity against methicillin resistant Staphylococcus aureus (MRSA). It was approved for clinical use in the USA, Europe and Russian Federation since 2010 for the treatment of the skin and soft tissue infection and community-acquired pneumoniae. In the present study there was used molecular typing of 24 isolates of MRSA with reduced susceptibility to ceftaroline. For 8 isolates belonging to different genetic lines (ST8, ST239 and ST228) and requiring MICs there were determined antibiotic concentrations preventing formation of resistant mutants (mutant prevention concentration) and the ranges of the mutant selection window (MSW). The last majority of the isolates with reduced susceptibility to ceftaroline (MIC of 2 mcg/ml) belonged to the clonal line ST228. The whole genome sequencing of two isolates of ST228 showed that they belonged to the epidemic South Germany genetic line and were characterized by the presence of mutations in PBP2a (N146K) and PBP2 (C197Y) responsible for reduced susceptibility. The highest rates of MPC (32 mcg/ml) and MSW (2-16 mcg/ml) were observed in the clinical isolates belonging to the genetic line ST8. The isolates of ST239 and ST228 had the selection window within 2-4 mcg/ml. No dependence of the MIC and MPC/MSW levels was detected.

Coagulase-negative staphylococci (CoNS) are considered as a reservoir of mobile genetic elements and first of all of the staphylococcal cassette chromosome mec (SCCmec), defining staphylococci resistance to beta-lactams. Types II, IV, IVa, V, VII and VIII SCCmec were detected among 95 staphylococcal strains isolated in different regions of the Russian Federation. Subtypes Cla, Clb, Clc and Cl SCCmec were also identified (class B mec complex and two complexes of ccrl and ccr2 genes recombinases). Some other cassette types carrying A, C1 and C2 classes of the mec complexes in combination with various recombinase genes were detected. The S.epidermidis isolates mainly formed cassettes carrying mec complex B, while the S.haemolyticus isolates had cassettes carrying classes C1 and C2 mec complex. Out of 9 isolates of S.hominis 5 isolates carried a new type cassette: class A mec complex in combination with the complex of the recombinase ccrl genes. SCCmec was not identified in S.capitis and S.pasteuri. Their representatives carried either mec complex (1 isolate of S.pasteuri) or the recombinase complexes (2 isolates of S.capitis). The detected SCCmec variants in CoNS could be a source of emergence of new genetic lines of MRSA.