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Antimicrobial effect of coffee extract on Streptococcus mutans.

The objective of this study was to investigate the in vitro antimicrobial activity of coffee on Streptococcus mutans, which is the major causative agent of dental caries in humans. The influence of the extraction/brewing process, brand, and coffee chemical compounds in the presence or absence of the aqueous extract was evaluated. The method of diffusion in agar was used to investigate the antimicrobial activity. Sterile disks were soaked with 20 μL samples, added to Mueller Hinton agar previously seeded with 10 cfu 24 h S. mutans and incubated at 37oC/48 h, in the presence of 5% CO2. The diameters of the inhibition zones were measured and submitted to statistical analysis. Every extract tested showed antimicrobial activity. Significant difference was observed on the pH values of the extracts and also on the pH and color characteristics of aqueous extracts from coffees of different brands. However, no significant difference was observed on the antimicrobial activity among ethanolic, aqueous (100oC/3 min), and espresso extracts and also among brands analyzed. No significant difference was observed on the antimicrobial activity among tested substances (2 mg/mL) by themselves; however, when associated with coffee aqueous extract, there was higher antimicrobial activity, except for chlorogenic acid.