Arginine Effect on Acid Synthesis by Streptococcus mutans UA159

Objectives: Arginine is receiving attention as a dentifrice additive. The effect of arginine on the production of acid by Streptococcus mutans strain UA159 when metabolizing sucrose was examined. Acid production, as well as the synthesis of lactic acid (lactate) and the potential generation of ammonium ion, were monitored during pH drop experiments where sucrose served as the carbon source.
Methods: Streptococcus mutans UA159 was grown in an enriched medium containing sucrose, harvested, washed twice and resuspened in artificial saliva [weakly buffered medium containing 3 mM K₂HPO₄, NaCl, MgCl₂ and CaCl₂ to which sucrose (10 mM) was added]. pH drop experiments were conducted with control cells, lacking arginine, as well as cells containing 0.5% arginine (approximately 29 mM). The synthesis of acid was monitored over a 2 hour time period and samples were saved for lactic acid and ammonium ion determinations.
Results: Control resting cells lowered the pH more rapidly than resting cells that contained 0.5% arginine. Preliminary analyses indicated that the resting cells containing arginine produced more lactate than did the control resting cells while but not generating ammonium. Together, it is suggested that the arginine-containing artificial saliva was acting as a buffering agent for the lactic acid produced by the S. mutans UA159. Experiments are underway to confirm these results.
Conclusions: The presence of 0.5% arginine in a weakly buffered S. mutans UA159 medium containing sucrose resulted higher pH by than when compared to the same medium lacking arginine. As no evidence of ammonium ion production was observed while increased amounts of lactate were produced by the arginine-containing cultures, it was concluded that the arginine may be acting as a weak buffer.