Background: Sortase A is an enzyme responsible for the covalent attachment of Pac proteins to the cell wall in Streptococcus mutans. It has been shown to play a role in modulating the surface properties and the biofilm formation and influence the cariogenicity of S. mutans. Curcumin, an active ingredient of turmeric, was reported to be an inhibitor for Staphylococcus aureus sortase A. The aim of this study was to investigate the inhibitory ability of curcumin against S. mutans sortase A and the effect of curcumin for biofilm formation. Methods: The antimicrobial activity of the curcumin to the S. mutans and inhibitory ability of the curcumin against the purified sortase A in vitro were detected. Western-blot and real-time PCR were used to analysis the sortase A mediated Pac protein changes when the S. mutans was cultured with curcumin. The curcumin on the S. mutans biofilm formation was determined by biofilm formation analysis. Results: Curcumin can inhibit purified S. mutans sortase A with a half-maximal inhibitory concentration (IC50) of (10.2 +/- 0.7) mu mol/l, which is lower than minimum inhibitory concentration (MIC of 175 mu mol/l Curcumin (15 mu mol/l) was found to release the Pac protein to the supernatant and reduce S. mutans biofilm formation. Conclusions: These results indicated that curcumin is an S. mutans sortase A inhibitor and has promising anti-caries characteristics through an anti-adhesion-mediated mechanism. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.