STUDY ON THE RESPONSE TO OXIDATIVE STRESS IN STREPTOCOCCUS MUTANS

Abstract

This study was t:arricd out to examine the rcsponses of Streptococcus mUlans, a major etiological agent or dental caries, to oxidative strcss caused by oxidative-damaging agents including H20 2, 8-hydroxyquinoline (8HQ) and plumbagin. The changes in the activity of protective enzymes: superoxide dismutase (SOD), NADH oxidase (NOX) and glutathione reductase (GR) and protein pattern of S. mutan. in respone to oxidative stress were detected when the cells were submitted to different oxidative stress conditions. The oxidative stress induced significant increase in SOD activities by 134, 113, and 240% compared to that of the control level (100%) when the cells were exposed to H20 2, 8HQ and plumbagin at concentrations of 0.5 mM, 21 JlM and 10 J.lM, respectively. The rate of lipid peroxidation was enhanced (as indicated by increasing the malonaldehydc-MDA contents) when the agent concentrations were increased. Also, glutathione level was remarkably higher compared to that of control when the cells treated with the agents espccially, plumbagin. Electrophoresis bands of SOD, NOX and GR of S. mutans indicated the difference in relative concentrations due to oxidative stress, particulally, H20 r treated samples. The cell protein profile obtained by SDS-PAGE revealed some up-regulated, down-regulated and new proteins. Clearly, the response of the mutans to the oxidative conditions resulted in complex and severe alterations in protein synthesis to further cell survival. Our findings suggest that the increased SOD activity and aSH level could be general stress responses of S. mutans to oxidative stress caused by H20 2• 8HQ and plumbagin and that, the new protein bands could be used as biomarkers for study the oxidative stress in bacteria.