Evaluation of the Effect of Four Herbal Extracts on Growth of Streptococcus mutans and Lactobacillus

Background and aim: Reduction of oral pathogens is very important in the healing of oral ulcers and infections. The side effects of chemical drugs have attracted more attention to medicinal plants. The present study assessed the effect of clove, thyme, garlic, and cinnamon ethanolic extracts on the growth of Streptococcus mutans (S. mutans) and Lactobacillus by measuring the inhibition zone diameter. Materials and methods: In this in-vitro experimental study, suspensions of standard strains of S. mutans (PTCC5027) and Lactobacillus (PTCC1608) were inoculated on Müller-Hinton agar using a sterile swab. 10 g of crushed and dried plants was dissolved in 100 ml of ethanol, and an ethanolic extract was obtained after passing through a filter and evaporation. 10 μl of each extract was poured onto blank discs which were placed on plates containing bacteria. A disc containing the control groups, including 0.2% chlorhexidine and a blank disc, was also placed on the plates. The plates were placed in a jar for 24 hours at 37°C and then the inhibition zone diameter around each disc was measured. Ten replicates were performed for each herbal extract. Data were analyzed by analysis of variance (ANOVA) and post hoc tests. Results: All four ethanolic herbal extracts were able to inhibit the growth of S. mutans and Lactobacilli. For both bacteria, the largest inhibition zone was observed with chlorhexidine, followed by clove, thyme, garlic, and cinnamon, respectively. There was a significant difference between the inhibition zone diameters formed by the extracts (P<0.01). Conclusion: Ethanolic extract of clove showed more prominent antibacterial effects than ethanolic extracts of thyme, garlic, and cinnamon.