Exploration of Endothelial Cell Invasion and Responses to Nicotine and Arginine by Streptococcus Mutans Serotype K Strains in a Sucrose-Induced Biofilm Lifestyle

Abstract

Streptococcus mutans, an inhabitant of oral biofilm or dental plaque, adheres to the tooth surface via protein antigen I/II (PA I/II). Pathologic lesions of atherosclerosis (AT) and infective endocarditis (IE) harbor S. mutans. Serotypes f and k strains with collagen binding protein genes cbm and cnm are uncommon in the mouth, but these are the most prevalent S. mutans strains in AT and IE tissues and can invade endothelial cells (EC) in vitro. Tobacco use increases the risk for cardiovascular and oral diseases. Oral S. mutans encounter many substances including nicotine. Arginine is present in saliva and the EC glycocalyx that coats and protects ECs from shear forces of blood flow. Prior studies demonstrated arginine alters S. mutans biofilm. This work characterizes S. mutans serotype k strains and serotype c strains, the most prevalent in the mouth. The effects of nicotine and arginine on biofilm mass, metabolic activity and EC invasion were investigated. Biofilm production by serotypes c and k strains did not differ; there were no differences in responses to nicotine and arginine between these serotypes. Increased production of biofilm was associated with the cbm and cnm genes. Nicotine increased biofilm for all strains whereas arginine plus nicotine reduced bacteria and the extracellular polymeric substances. Previous EC invasion studies were performed with planktonic cultures of S. mutans; therefore, EC invasion by biofilm was evaluated. Significant factors for EC invasion by S. mutans are presence of the cbm gene and lack of PA I/II expression on the bacterial cell surface. Presence of the cnm gene increased EC invasion by biofilm but not planktonic cells. Planktonic cells of six strains invaded better than biofilm, whereas four strains showed increased invasion by biofilm cells. Neither nicotine nor arginine significantly altered the ability of S. mutans biofilm cells to invade ECs. Not all strains with cbm or cnm and no PA I/II expression invaded EC. A strain with PA I/II expression and without cbm and cnm genes invaded EC. While cbm, cnm and PA I/II expression are predictors of EC invasion, additional mechanisms for EC invasion by S. mutans remain to be revealed.