Stevia rebaudiana is a plant grown primarily in South America and goes by such names as sweet grass, honey-leaf, sweet herb or sweet-leaf. The leaves contain steviol glycosides, which contribute to sweetness. Today, several non-caloric sweetener Stevia products are widely available for purchase. Steviol glycosides have proven antimicrobial properties pertaining to microbes specifically residing within biofilms in the human oral cavity. In addition, its anticancer and antifungal properties have also been investigated. Specifically, compound Rebausdioside A is a steviol glycoside that expresses antimicrobial properties. The purpose of this study was to test Rebaudioside A in an organic mixture of natural Stevia extract for its effectiveness at neutralizing Streptococcus mutans and Lactobacillus acidophilus. These microbes are known for causing dental caries in humans. Freeze-dried pellets were rehydrated in tomato juice for L. acidophilus and in Brain Heart Infusion (BHI) broth for S. mutans. After successful inoculation on Tryptic Soy Agar (TSA) with 5% sheep blood plates, S. mutans were inoculated on BHI agar plates and tested against Aqueous 99% Rebaudioside A, 70% Ethyl Alcohol with 99% Rebaudioside A Extract, and 4% Chlorhexidine Gluconate (standard control for susceptibility determination) using a well-plate method. The alcohol extracts were synthesized by adding solid extract into liquid alcohol and filtered using muslin cloth and Whatman No. 1 filter paper. After evaporation, alcohol extracts were diluted with DI water to 50% concentration. On the other hand, L. acidophilus did not rehydrate successfully and was replaced with a Human Saliva swab. Results from three trials showed that 4% Chlorhexidine Gluconate performed as expected with a mean zone of inhibition for S. mutans at 23.75mm and for Human Saliva at 32.25mm. Organic aqueous Stevia extract did not show the same effectiveness even when combined with 70% Ethyl Alcohol. A possible explanation could be that S. mutans converted the alcohol into acetaldehyde as it possesses alcohol dehydrogenase. In addition, other studies have shown that ethanol is not able to penetrate the gram-positive cell wall of S. mutans. Aqueous Stevia extract showed zones of inhibition ranging from 9-11mm for the Human Saliva inoculates but for Stevia in combination with 70% Ethyl Alcohol, again no bacterial growth was inhibited.

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