Proteomic analysis of the Enterococcus faecalis V583 strain and clinical isolate V309 under vancomycin treatment

To understand the molecular mechanisms of bacteria resistance to glycopeptides, we obtained proteomic profiles of vancomycin-resistant Enterococcus faecalis V583 (reference strain) and V309 (clinical isolate) passaged with and without the drug. The specificity and reversibility of vancomycin resistance genes induced in V583 and V309 were further studied over time. By semiquantitative RT-PCR of vancomycin-treated versus untreated samples of both strains, 28 (V583) or 20 (V309) up-regulated proteins, 8 (V583) or 6 (V309) down-regulated proteins, and 1 (V583) or 4 (V309) proteins with mobility changes in 2-DE gel analysis were identified. Some of these proteins have known vancomycin resistance functions or are related to virulent factors, stress, metabolism, translation, and conjunction, which would help Enterococcus survive under drug selection. Vancomycin induced specifically and reversibly VanA, VanX, VanB, and VanXB. Notably, 6 proteins (Pgm, Ldh, Gap-2, RpsB, EF2076, and sex pheromone cAD1 precursor lipoprotein) exhibited clear post-translational modifications. Vancomycin induced phosphorylation of Ser/Thr in Ldh, Gap-2, and sex pheromone cAD1 precursor lipoprotein (EF3256), newly identified here as enterococcal phosphoproteins. Our data suggest that phosphorylated EF3256 is normally active in E. faecelis, whereas EF3256-P together with oppA-like protein may play a key role in the regulation of pheromone and transmission of conjugation plasmids.