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|Issue Date: ||20-Feb-2012|
|Authors: ||Bertuccio, Taschia Giuseppina|
|Title: ||Modulating activity of vancomycin and daptomycin on the expression of gene involved in reduced glycopeptide susceptibility in Staphylococcus aureus|
|Abstract: ||In the last decade the increased use of vancomycin and teicoplanin (glycopeptides), as the first-line antibiotics for the therapy of infections due to Methicillin Resistant Staphylococcus aureus (MRSA), has led to the emergence of Vancomycin Intermediate Staphylococcus aureus i.e. heterogeneous Vancomycin-Intermediate-Staphylococcus aureus (hVISA) and homogeneous Vancomycin-Intermediate-Staphylococcus aureus (VISA). The genetic basis of reduced vancomycin susceptibility has been the subject of different papers: numerous genes (autolytic, cell-wall turnover and cell-envelope positive charge) and regulatory loci have been reported to be associated with glycopeptide intermediate resistance.
Moreover, some recent papers reported a positive correlation between vancomycin and daptomycin reduced susceptibility but the molecular machinery involved in this cross resistance, and the molecular and phenotypic changes of hVISA and VISA strains are not well understood.
The goal of our study was to investigate: the molecular basis of vancomycin reduced susceptibility, and the activity of vancomycin and daptomycin on the expression of the genes involved.
The study was performed on a sample of strains including VSSA, hVISA and VISA, grown with or without vancomycin or daptomycin, and carried out by phenotypic assay (autolysis in Triton x-100, ¿-haemolysin production on 5% sheep blood agar) and by quantitative relative real time RT-PCR on the genes involved in: autolysis (atl, lytM), cell-wall turnover (sceD), membrane charges (mprF, dltA) and regulatory mechanisms (agr locus, graRS, walRK).
Our results show that hVISA and VISA strains, with respect to VSSA, are characterized by an up-regulation of sceD, a down-regulation of rnaIII (agr locus) and an up-regulation of mprF in Mu3 (hVISA) and dltA in Mu50 (VISA). The VISA strain, in addition, is characterized by a down-regulation of atl and lytM genes versus hVISA and, obviously, VSSA.
At the light of these results we can conclude that hVISA and VISA strains possess an increased cell-wall turnover and positive charge, but a reduced agr locus functionality: these features are responsible for reduced vancomycin susceptibility and this distinguishes hVISA and VISA from VSSA. Furthermore, the VISA phenotype comes out from hVISA when it acquires a reduced both autolysis and net negative cell-envelope charge.
Another outcome is that vancomycin and daptomycin act in the same way, stimulating hVISA to acquire the VISA behaviour and increasing, in VISA, the cell-wall pathway at the basis of the intermediate vancomycin phenotype. Moreover, daptomycin induces a charge repulsion mechanism in hVISA and VISA due to mprF up-regulation.|
|Appears in Collections:||Area 06 - Scienze mediche|
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|BRTTCH75B57C351Q-Tesi dottorato sottomessa.pdf||Tesi di dottorato||1,7 MB||Adobe PDF||View/Open
|BRTTCH75B57C351Q-Frontespizio Interno.pdf||Frontespizio||434,69 kB||Adobe PDF||View/Open
|BRTTCH75B57C351Q-table of contents.pdf||Table of contents-Indice||343,04 kB||Adobe PDF||View/Open
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