Comparative proteomic analysis of Staphylococcus aureus strains with differences in resistance to the cell wall-targeting antibiotic vancomycin

Three isogenic strains derived from a clinical vancomycin-intermediate Staphylococcus aureus isolate were examined by comparative protein abundance analysis. Subcellular fractionation was followed by protein separation in 2-DE gels and spot identification by MALDI-TOFTOF-MS and LC-MS/MS. Sixty-five significant protein abundance changes were determined. Numerous enzymes participating in the purine biosynthesis pathway were dramatically increased in abundance in strain VP32, which featured the highest minimal inhibitory concentration for vancomycin, compared to strains P100 and HIP5827. Peptidoglycan hydrolase LytM (LytM) and the SceD protein, a putative transglycosylase, were increased in abundance in the cell envelope fraction of strain VP32, whereas the enzyme D-Ala-D-Ala ligase was decreased in its cytosol fraction. Furthermore, penicillin-binding protein 2 (PBP2) had substantially higher activity in strain VP32 compared to that in strain HIP5827. LytM, PBP2 and D-Ala-D-Ala ligase catalyze reactions in the biosynthesis or the metabolism of cell wall peptidoglycan. It is plausible that expression and activity changes of these enzymes in strain VP32 are responsible for an altered cell wall turnover rate, which has been observed, and an altered peptidoglycan structure, which has yet to be elucidated for this highly vancomycin-resistant strain.