Background & Objectives: Dental caries is the most important disease caused by some bacteria specially Streptococcus Mutans from Viridans family. The aim of this study is to evaluate the inhibitory effect of Chlorella vulgaris extract on growth, proliferation, and biofilm formation of Streptococcus mutans.

Materials & Methods: Microalgae Chlorella vulgaris was extracted via maceration using chloroform, methanol, and acetone (2/1/1) as solvents. The antibacterial activities were evaluated through methods such as disk diffusion, well diffusion, minimal inhibitory concentration (MIC), and minimal bactericidal concentration (MBC) besides, the anti-biofilm formation of Chlorella vulgaris extract was indicated. In the present study, a method utilizing brine shrimp lethality was used to screen the toxicity of Chlorella vulgaris extract, and the mortality of brine shrimps was counted by Magnifying glass in a 24-hour period.

Results: The results of disc diffusion and well diffusion of Chlorella vulgaris extract revealed the averages of 16.5 and 23 mm zones of inhibition in Mueller-Hinton agar, respectively. The minimal inhibitory concentration was 25 mg/ml and the minimal bactericidal concentration was 50 mg/ml. The anti-biofilm formation concentration of Chlorella vulgaris extract was 50 mg/ml, and the concentration of brine shrimp toxicity was100 mg/ml.

Conclusion: The present study showed that Chlorella vulgaris extract has more significant antimicrobial properties than ampicillin and is able to eliminate Streptococcus mutans biofilm.