Comparative Analysis of Chlorhexidine Derivatives and Alternative Agents on Streptococcus mutans Viability, Biofilm Formation, and Gene Expression.

This study evaluates the antimicrobial and antibiofilm effects of chlorhexidine and related compounds against S. mutans, focusing on bacterial viability, biofilm formation, and expression of key biofilm genes. Eight compounds were tested for their chemical properties, MICs, and interactions via FIC analyses. Time-kill assays assessed bactericidal activity over 24 h, while cytotoxicity was evaluated in human gingival fibroblasts. Gene expression of biofilm-related genes was analyzed to determine transcriptional modulation. Chlorhexidine gluconate and alexidine showed the strongest antimicrobial activity, with MICs of 2 μg/mL against the reference strain and 4 μg/mL for clinical isolates. Time-kill results demonstrated bacterial reductions from ~7.2 to < 1.0 log CFU/mL in the reference strain but less effect in clinical isolates. Chlorhexidine reduced biofilm biomass by nearly 19% at 48 h, whereas amoxicillin increased biofilm formation by over 12%. Cytotoxicity varied, with proguanil showing high cell viability (90%), while chlorhexidine and alexidine reduced viability to 50-70%. Gene expression analyzes revealed significant downregulation of gtfD and brpA by chlorhexidine and analogs, contrasting with mild upregulation by amoxicillin. These findings highlight chlorhexidine compounds as effective anti-biofilm agents, emphasizing the need for continued exploration of alternatives and combination therapies to enhance dental caries treatment.