The current project investigates the proteomic profiles of essential genes, mass spectrometric analysis respectively, under impact of sub-inhibitory concentration of ampicillin (0.125 micro gm/ml), to elucidate the S. sanguinis stress response mechanisms on a temporal basis and define “pathogenesis signatures” as potential therapeutic targets. We further believe that the current findings will help characterize a bacterial model for studying the dynamics of essential genes under clinically relevant stress factors (antibiotic treatment) and assist in designing evidence-based guidelines for treatment in clinical settings.