Dose-dependent Antimicrobial Activity of Grape Seed Extract Against Different Microorganisms

Objectives: The dentin bioactivity of proanthocyanidins-rich extracts (PACs), such as grape seed extract (GSE), has been successfully demonstrated. However, its antimicrobial effect is still not fully elucidated. Effective anti-microbial properties of GSE would increase the applications of plant-derived PACs in dentistry. Objectives: the aim of this study was to assess the antimicrobial activity of a GSE (Polyphenolics MegaNatural, CA, USA) against planktonic cells of Streptococcus mutans, Sm (ATCC 25175), Methicillin-resistant Staphylococcus aureus, MRSA (ATCC 33591) and Candida albicans, Ca (ATCC 90028).
Methods: for this purpose, a starting solution of GSE was prepared in HEPES buffer (0.02 M) at 6.5% (w/v) and pH 7.4. Cells of Sm, MRSA and Ca were incubated in 96-well microtiter plate for 24 h at 37 °C and exposed to serial 2-fold dilution of GSE (from 32.50 to 0.12 mg/mL) in BHI, TSB and RPMI-1640, respectively. After incubation, 100 μL-aliquots from each well were 10-fold serially diluted and inoculated, in duplicate, on culture media for each microorganism for 48 h at 37 °C. After incubation, the colony-forming units per milliliter (CFU/mL) were then calculated, and a log transformation was plotted. These experiments were performed in three different occasions.
Results: ANOVA and Tukey’s tests (p=0.05) showed that the GSE exhibited dose-dependent antimicrobial activity against Sm, MRSA and Ca. GSE showed bactericidal effects against Sm and MRSA at 32.25 mg/mL and 4.06 mg/mL, respectively, and fungicidal effect against Ca at 32.25 mg/mL. Additionally, a significant reduction in the number of CFU/mL (inhibitory effect) also was observed at 16.25 mg/mL for Sm, at 2.03 mg/mL and 1.02 mg/mL for MRSA and from 16.25 to 1.02 mg/mL for Ca.
Conclusions: the GSE evaluated exhibited dose-dependent antimicrobial activity against planktonic cells of Sm, MRSA and Ca and it had potential to be a natural antimicrobial agent for multiple applications.