Ursolic acid disrupts cariogenic biofilms with selective antibacterial activity against Streptococcus mutans and Streptococcus sobrinus

Abstract

Prevention of dental caries requires effective control of biofilm-forming Streptococcus spp. The present study evaluated the antimicrobial and antibiofilm properties of ursolic acid (UA) and beta-sitosterol against cariogenic bacteria. UA demonstrated selective antimicrobial activity, with MIC/MBC values of 8 and 16 μM against Streptococcus mutans and Streptococcus sobrinus, respectively. At 16 μM, UA reduced biofilm adherence by 95% and 90% in S. mutans and S. sobrinus, respectively. Confocal microscopy revealed a dose-dependent reduction in biofilm thickness, decreasing from 35.2 ± 2.3 μm to 17.3 ± 1.5 μm for S. mutans and from 64.3 ± 1.8 μm to 42.1 ± 1.2 μm for S. sobrinus following treatment with 64 μM UA. At this concentration, bacterial viability decreased to 40% and 62% for S. mutans and S. sobrinus, respectively. In comparison, 0.12% chlorhexidine (positive control) reduced biofilm thickness to 15.1 ± 2.5 μm and 32.5 ± 1.9 μm, with viability decreasing to 36% and 52% for S. mutans and S. sobrinus, respectively. Unlike UA, beta-sitosterol showed negligible antibacterial activity. These findings demonstrate the potential of UA as a promising natural therapeutic agent against cariogenic biofilms, although its efficacy remains lower than that of chlorhexidine.