Reduced Glutathione Effect on Antimicrobial Properties of Silver Diamine Fluoride

Objectives: Reduced glutathione (GSH) has been found to alleviate silver diamine fluoride (SDF)-induced tooth structure discoloration and toxicity to pulp cells. This present study aimed to investigate effects of GSH on the antimicrobial properties of SDF.
Methods: Single- and dual-species biofilms of Streptococcus mutans and Candida albicans were developed. Biofilms were treated for 5 minutes with either SDF or SDF+GSH. Metabolic activity and total biofilm biomass post treatment were determined using AlamarBlue and crystal violet assays, respectively. Microbial cell numbers and biofilm regrowth after treatment were also assessed. Additionally, the effect of preconditioning well surfaces with SDF or SDF+GSH on single- and dual-species biofilm formation and on non-adherent microbial cell counts was investigated. One-way ANOVA and Tukey post hoc tests were used for statistical analyses (α=0.05).
Results: SDF or SDF+GSH significantly reduced metabolic activities and recovered colony forming units (CFU) of biofilms compared to untreated controls. Both treatments also prevented regrowth of tested biofilms. GSH did not reduce antibiofilm effects of SDF. Crystal violet staining showed that biofilm treatment and preconditioning surfaces with SDF or SDF+GSH resulted in notable background staining compared with unconditioned controls. This was expected, as SDF is known to cause recalcitrant surface staining. However, this effect was significantly lower for SDF+GSH compared to SDF. Based on metabolic activity and recovered CFUs, surface preconditioning with SDF or SDF+GSH was found to significantly inhibit biofilm formation.
Conclusions: SDF exhibited potent antimicrobial effects towards biofilms. In addition, preconditioned surfaces with SDF displayed antimicrobial activity and inhibited biofilm formation. These findings were unaffected by the presence of GSH. GSH is a promising potential additive to ameliorate unfavorable effects of SDF while maintaining its desired antimicrobial properties.