Inhibition effect of garlic (Allium sativum) extract on Streptococcus sanguinis biofilm formation involving bacterial motility mechanism

Introduction: Streptococcus sanguinis is a primary colonizer in oral biofilm formation, often implicated in infective endocarditis. Methods to control oral biofilm formation are yet to be developed. Garlic (Allium sativum) has shown antimicrobial activities against many pathogen species. We sought to observe the potential of garlic extract to inhibit bacterial adherence to hydroxyapatite (HA) discs as a model of the tooth surface. Methods: Susceptibility of S. sanguinis ATCC 10556 to garlic extract was examined by minimum inhibitory concentration (MIC) test using broth microdilution method. For bacterial adherence assay, saliva-coated HA discs were incubated with various concentrations of extract then stimulated with S. sanguinis ATCC 10556 suspension. Adherent bacteria were stained with 0.1% crystal violet and measured at 595 nm using a microplate reader. A qualitative method to test bacterial motility was performed using Motility Indole Ornithine (MIO) medium. Results: The result of minimum inhibitory concentration test showed that MIC value for garlic ethanolic extract was at a concentration of 625 μg/ml. Moreover, garlic extract inhibited bacterial adherence to HA discs starting at concentration of 62.5 μg/ml. The inhibition of bacterial motility can be observed, indicated as limited the diffused growth of bacteria closer to the inoculating line. Observation using SEM confirmed these results. Conclusion: This present study suggest that garlic extract has the ability to inhibit S. sanguinis adherence to HA discs involving inhibition of bacterial motility, with the optimal concentration being 500 μg/ml.