Effect of phototherapy on the metabolism of Streptococcus mutans biofilm based on a colorimetric tetrazolium assay

Grace F. Gomez, Ruijie Huang, George Eckert, Richard L. Gregory

Research output: Contribution to journalArticle

3 Scopus citations


The aim of this in vitro study was to determine the effect of violet-blue light on the metabolic activity of early Streptococcus mutans biofilm, reincubated at 0, 2, and 6 h after 5 min of violet-blue light treatment. S. mutans UA159 biofilm cells were cultured for 12 to 16 h in microtiter plates with Tryptic Soy broth (TSB) or TSB with 1% sucrose (TSBS) and irradiated with violet-blue light for 5 min. After irradiation, the plates were reincubated at 37°C for 0, 2, or 6 h in 5% CO2. Colorimetric tetrazolium salt reduction assay was used to investigate bacterial metabolic activity. Mixed model ANOVA was used to find the difference between the violet-blue light treated and nontreated groups. Bacterial metabolic activity was significantly lower in the violet-blue light group for TSB than in the nontreated group (P < 0.0001) regardless of recovery time. However, the differences between metabolic activity in the treated groups without sucrose decreased over time. For TSBS, metabolic activity was significantly lower with violet-blue light at 0 and 2 h. Violet-blue light inhibited the metabolic activity of S. mutans biofilm cells in the light-treated group. This finding may present a unique treatment method for patients with active caries.

Original languageEnglish (US)
Pages (from-to)242-246
Number of pages5
JournalJournal of Oral Science
Issue number2
StatePublished - Jun 2018



  • Biofilm
  • Streptococcus mutans
  • Violet-blue light
  • XTT assay

ASJC Scopus subject areas

  • Dentistry(all)

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