L wall thickness of S. aureus [11]. Collectively, these observations are consistent with a previous report showing that vancomycin affects the expression of CWSSassociated genes [12]. Another differentially expressed protein, GpmA, functions in cellular metabolism. GpmA catalyzes the interconversion of 2phosphoglycerate and 3-phosphoglycerate and is therefore involved in the glycolytic pathway [31]. As a key enzyme in glycolysis and energy metabolism, GpmA is a potential target for novel antibiotics [31]. This study is the first to report that GpmA is up-regulated in hVISA. IsaA, which is involved in cell wall biogenesis, was also overexpressed in both hVISA isolates, as shown in our comparative proteomics results. IsaA cleaves peptidoglycan and thus plays a significant role in peptidoglycan turnover, cell wall crosslinking, and cell division [32]. Therefore, IsaA over-expression could be associated with the thickened cell walls of hVISA strains, which may be related to hVISA resistance. Another comparative proteomics study found that IsaA is up-regulated in the VISA strain Mu50, which is similar to our result [16]. The lack of RNAIII can lead to the over-expression of IsaA [33]. Several studies have indicated that VISA is characterized by agr dysfunction or RNAIII down-regulation [6,34,35]. A cDNA microarray study showed that IsaA is up-regulated in VRSA strains [36]. Therefore, the isaA gene may have an important function in S. aureus resistance to vancomycin.To validate the accuracy of the results of our comparative proteomics analysis, 6 pairs of isogenic VSSA and hVISA strains isolated from the same patient, unrelated VSSA (n = 30) and hVISA (n = 24) strains, and 15 pairs of persistent VSSA strains were selected for confirmation by qRT CR. Analysis of the isogenic strains showed that isaA, msrA2, gpmA, and ahpC were significantly up-regulated in most of the hVISA strains compared with the VSSA strains, which was partly consistent with the results of comparative proteomics. However, only isaA was significantly up-regulated in hVISA strains compared with the unrelated VSSA strains. Therefore, the over-expression of isaA may be related to hVISA resistance. Analysis of the 15 pairs of persistent VSSA strains showed no differences in the expression of the identified genes, 23148522 which indicates that these genes are not associated with persistent infection. The present study has several limitations. First, the functionality of the identified genes could not be assigned in the absence of gene knockout Xposure to the recombinant proteins, cells were fixed and stained to experiments or further studies. Furthermore, the gene expression Title Loaded From File changes observed may be a consequence of vancomycin resistance and not causal of this phenotype. For example, these changes may be necessary to compensate for increased cell wall thickness or a consequence of reduced growth rate. In summary, five differentially expressed proteins, IsaA, MsrA2, Asp23, GpmA, and AphC, were identified in two pairs of isogenic VSSA and hVISA strains via comparative proteomics analysis. The results of qRT-PCR showed that the isaA gene was significantly up-regulated in most of the clinical hVISA isolates, suggesting a relation between increased expression of isaA and hVISA resistance.AcknowledgmentsThe authors would like to thank International Science Editing for critically revising the manuscript.Author ContributionsConceived and designed the experiments: HW MC. Performed the experiments: HC YL CZ FZ. Analyzed the data: HC YL HW. Contributed reagents/mate.L wall thickness of S. aureus [11]. Collectively, these observations are consistent with a previous report showing that vancomycin affects the expression of CWSSassociated genes [12]. Another differentially expressed protein, GpmA, functions in cellular metabolism. GpmA catalyzes the interconversion of 2phosphoglycerate and 3-phosphoglycerate and is therefore involved in the glycolytic pathway [31]. As a key enzyme in glycolysis and energy metabolism, GpmA is a potential target for novel antibiotics [31]. This study is the first to report that GpmA is up-regulated in hVISA. IsaA, which is involved in cell wall biogenesis, was also overexpressed in both hVISA isolates, as shown in our comparative proteomics results. IsaA cleaves peptidoglycan and thus plays a significant role in peptidoglycan turnover, cell wall crosslinking, and cell division [32]. Therefore, IsaA over-expression could be associated with the thickened cell walls of hVISA strains, which may be related to hVISA resistance. Another comparative proteomics study found that IsaA is up-regulated in the VISA strain Mu50, which is similar to our result [16]. The lack of RNAIII can lead to the over-expression of IsaA [33]. Several studies have indicated that VISA is characterized by agr dysfunction or RNAIII down-regulation [6,34,35]. A cDNA microarray study showed that IsaA is up-regulated in VRSA strains [36]. Therefore, the isaA gene may have an important function in S. aureus resistance to vancomycin.To validate the accuracy of the results of our comparative proteomics analysis, 6 pairs of isogenic VSSA and hVISA strains isolated from the same patient, unrelated VSSA (n = 30) and hVISA (n = 24) strains, and 15 pairs of persistent VSSA strains were selected for confirmation by qRT CR. Analysis of the isogenic strains showed that isaA, msrA2, gpmA, and ahpC were significantly up-regulated in most of the hVISA strains compared with the VSSA strains, which was partly consistent with the results of comparative proteomics. However, only isaA was significantly up-regulated in hVISA strains compared with the unrelated VSSA strains. Therefore, the over-expression of isaA may be related to hVISA resistance. Analysis of the 15 pairs of persistent VSSA strains showed no differences in the expression of the identified genes, 23148522 which indicates that these genes are not associated with persistent infection. The present study has several limitations. First, the functionality of the identified genes could not be assigned in the absence of gene knockout experiments or further studies. Furthermore, the gene expression changes observed may be a consequence of vancomycin resistance and not causal of this phenotype. For example, these changes may be necessary to compensate for increased cell wall thickness or a consequence of reduced growth rate. In summary, five differentially expressed proteins, IsaA, MsrA2, Asp23, GpmA, and AphC, were identified in two pairs of isogenic VSSA and hVISA strains via comparative proteomics analysis. The results of qRT-PCR showed that the isaA gene was significantly up-regulated in most of the clinical hVISA isolates, suggesting a relation between increased expression of isaA and hVISA resistance.AcknowledgmentsThe authors would like to thank International Science Editing for critically revising the manuscript.Author ContributionsConceived and designed the experiments: HW MC. Performed the experiments: HC YL CZ FZ. Analyzed the data: HC YL HW. Contributed reagents/mate.
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