ABSTRACT
Aims: VraSR and GraSR were shown to be important in conferring intermediate vancomycin resistance in VISA. Nevertheless, the exact mechanism modulated by these systems leading to the development of VISA remains unclear. We employed a proteomic approach to determine the VraS and GraR regulons and subsequently derive the possible vancomycin resistance regulatory pathway(s) in the Mu50 lineage of Staphylococcus aureus. Methodology and results: Staphylococcus aureus strains Mu50Ω, Mu50Ω-vraSm and Mu50Ω-vraSm-graRm are isogenic strains with ascending levels of vancomycin resistance. Total proteins were extracted from the 3 strains and trypsin digested prior to protein isolation and identification by LC-ESI MS/MS and PLGS 2.4. Expression profiles of resulting proteins were analyzed using Progenesis LC/MS software. Differential expression profiles revealed 3 regulons, each controlled by VraS (Mu50Ω-vraSm vs Mu50Ω), GraR (Mu50Ω-vraSm-graRm vs Mu50Ω-vraSm) and VraS-GraR (Mu50Ω-vraSm-graRm vs Mu50Ω), respectively. The regulon down-regulated by VraS in Mu50Ω-vraSm were proteins associated with virulence (MgrA, Rot, and SarA), while GraR up-regulated resistance-associated proteins (TpiA, ArcB and IsaA) in Mu50Ω-vraSm-graRm. The VraS-GraR regulon mediated both up-regulation of resistance-associated proteins (ArgF, ArcB, VraR and SerS) and down-regulation of virulence-associated protein GapB. Conclusion, significance and impact of study: Down-regulation of virulence- in concert with up-regulation of resistance-associated proteins appears to be integral for development of intermediate-vancomycin resistance in the Mu50 lineage of S. aureus.
Subject(s)
Staphylococcus aureusABSTRACT
<p><b>OBJECTIVE</b>To genotypically characterize methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from medical and surgical wards in Universiti Kebangsaan Malaysia Medical Centre (UKMMC) in 2009.</p><p><b>METHODS</b>MRSA strains were collected and molecularly typed by pulsed-field gel electrophoresis (PFGE).</p><p><b>RESULTS</b>PFGE typing on 180 MRSA isolated in UKMMC identified 5 pulsotypes (A-E) and 6 singletons, where pulsotypes B and C were suspected to be divergent clones originating from a single ancestor. This study also showed that most MRSA strains were isolated from swab (119 isolates), followed by blood (22 isolates), tracheal aspirate (11 isolates) and sputum (10 isolates). On the other hand, urine and bone isolates were less, which were 4 and 1 isolates, respectively. The distribution of different pulsotypes of MRSA among wards suggested that MRSA was communicated in surgical and medical wards in UKMMC, with pulsotype B MRSA as the dominant strain. Besides, it was found that most deceased patients were infected by pulsotype B MRSA, however, no particular pulsotype could be associated with patient age, underlying disease, or ward of admittance.</p><p><b>CONCLUSIONS</b>Five pulsotypes of MRSA and 6 singletons were identified, with pulsotype B MRSA as the endemic strains circulating in these wards, which is useful in establishment of preventive measures against MRSA transmission.</p>