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Glycopeptides are the basis of the treatment of infections caused by MRSA (Methicillin-Resistant Staphylococcus aureus). Previously, it was demonstrated that antibiotic tolerant phenotypes are formed during selection of resistance under the influence of high concentrations of antibiotics. The present study uses a similar in vitro selection model with vancomycin. Clinical isolates of MRSA belonging to genetic lines ST8 and ST239, as well as the MSSA (ATCC29213) strain, were included in the experiment. Test isolates were incubated for five hours in a medium with a high concentration of vancomycin (50 μg/ml). Test cultures were grown on the medium without antibiotic for 18 hours after each exposure. A total of ten exposure cycles were performed. Vancomycin was characterized by bacteriostatic action; the proportion of surviving cells after exposure was 70–100%. After selection, there was a slight increase in the MIC to vancomycin (MIC 2 μg/ml), teicoplanin (MIC 1.5–3 μg/ml) and daptomycin (MIC 0.25–2 μg/ml). According to the results of PAP analysis, all strains showed an increase in the area under curve depending on the concentration of vancomycin after selection, while a heteroresistant phenotype (with PAP/AUC 0.9) was detected in three isolates. All isolates showed walK mutations (T188S, D235N, E261V, V380I, and G223D). Exposure to short-term shock concentrations of vancomycin promotes the formation of heteroresistance in both MRSA and MSSA. Formation of VISA phenotypes is possible during therapy with vancomycin.

Klebsiella pneumoniae is the most common cause of nosocomial infections. There are two main types of K.pneumoniae (Kp) - classical K.pneumoniae (cKp) and hypervirulent K.pneumoniae (hvKp). In 2015, an outbreak of nosocomial infections caused by Kp was recorded in China for the first time, showing signs of hypervirulence and multidrug resistance (production of blaKPC-2). The purpose of this work is to assess the frequency of rectal colonization of patients admitted to a planned treatment in a cancer hospital with virulent and multidrug resistant strains of Kp and Pseudomonas aeruginosa. The study included 168 patients, 156 isolates of gram-negative bacteria were isolated from their rectal samples. Only one P.aeruginosa isolate turned out to be a blaVIMproducer. 30 isolates of Klebsiella spp.: Kp n=25; K.oxytoca n=3; K.planticola n=1; K.variicola n=1. Producers of carbapenemases have not been identified among them. Hypervirulence markers were detected in two of the three K.oxytoca isolates: in one (string-test «-») - all 5 genes (iucA,prmpA,prmpA2, iroB,peg-344), as well as two additional virulence genes, terB and irp2; in the second (string-test «+») - rmpA and irp2. A hypermucoid phenotype was observed in six Kp isolates and one K.oxytoca. Markers of hypervirulence, presumably with plasmid localization, were found in the Kp isolates: iucA (aerobactin), n=3; prmpA (hypermucoid phenotype regulator), n=3; iroB (salmohelin), n=2; and also, peg-344 (inner membrane conveyor), n=4; virulence determinants of presumably chromosomal localization: terB, n=1 and irp2, n=8. TerB and irp2 were also found in the K.variicola isolate. It is obvious that rectal carriage of bacteria is a real problem as it may be a constant reservoir and source of virulence genes, along with resistance genes.