Inhibitory Effects of Mulberry (Morus alba) Ethanolic Extract on Streptococcus mutans Biofilm Formation

Objectives: To evaluate the susceptibility of S. mutans (ATCC 25175) and three S. mutans clinical isolates from Thai children to three concentration of mulberry extract and to analyze the inhibition effect on biofilm of each strain using confocal scanning electron microscopy (CLSM). Materials and Methods: Obtained S. mutans clinical isolates from children (aged 3.5-10-years) who came to the Pediatric Dental Clinic, Faculty of Dentistry, Chulalongkorn University, Bangkok. Three concentration of mulberry extract were tested (125, 250, 500 mg/ml). The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were carried out. Incubated all S. mutans strains for 5 and 10 hours to form biofilm suitable for the susceptibility tests. The biofilm inhibition effect of mulberry extract also further evaluated using CLSM. Data was expressed as mean ± standard deviation (SD). The Kruskal-Wallis Test was used to compare the experimental and control groups (significance at 95%). Results: The MIC of mulberry extract was not able to visualize due to the darkness of the solution and precipitations. The MBC were in the range of 125-500 mg/ml. All strains tested were sensitive to all mulberry extract concentrations (> 99.88%) when compared to the controls. All strains pre form biofilm at 5 and 10 hours were inhibited after 5 and 10 minutes exposure to the mulberry extract at the concentration of 500 mg/ml which showed the percentage of inhibition at > 99.96-100% and > 99.93-100% compared to the control, respectively. All concentrations of the mulberry extract inhibited biofilm formation of all strains visualized by CLSM. The effects were dose-dependent. The 500 mg/ml concentration exhibited a significant inhibitory effects on S. mutans (ATCC 25175) (p = 0.013), S. mutans clinical isolate N006, N029 and N113 (p = 0.016) when compared to the control group. Conclusions: Mulberry extract at the 500 mg/ml concentration showed excellent antibacterial activity