Assessment of Oral Microbial Viability by 2,6-Dichlorophenolindophenol a Redox Agent

<b>Background/Objectives:</b> This investigation evaluated 2,6-Dichlorophenolindophenol (DCIP), a redox dye, as a colorimetric reagent for rapid quantification of oral bacteria and examined the antimicrobial effects of oral hygiene formulations. <b>Methods/Results:</b> Viable microbial cells reduce DCIP, resulting in a loss of its blue color which can be measured spectrophotometrically. Strains of <i>Actinomyces viscosus</i>, <i>Veillonella atypica</i>, <i>Aggregatibacter actinomycetemcomitans</i>, <i>Streptococcus mutans</i> and <i>Candida albicans</i> grown in the laboratory reduced DCIP. Significant correlations between increasing viable plate counts and DCIP reduction were noted for strains of oral organisms. Intact microbial cells reduced DCIP, with insignificant reductions observed by spent microbial media or bacteria free culture media. Organisms inactivated by either heat or cold demonstrated significantly lower DCIP reduction in comparison to metabolically intact organisms grown under optimal conditions. <b>Conclusions:</b> DCIP reduction provided a rapid and accurate method to evaluate antimicrobial effects of clinical proven mouthwashes formulated with cetylpyridinium chloride or chlorhexidine and toothpastes for a range of oral bacteria. Together, these results identify a rapid, low-cost method using common laboratory equipment to enumerate oral organisms with a visual outcome.