Effect of continuous exposure to chlorhexidine digluconate on competence and genetic transformation of Streptococcus mutans

• Grant number: 24/21471-6
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: January 05, 2026
• End date: March 04, 2026
• Field of knowledge: Health Sciences - Dentistry
• Principal Investigator: Antônio Pedro Ricomini Filho
• Grantee: Luiza Bittencourt de Borba
• Supervisor: Fernanda Cristina Petersen
• Host Institution: Faculdade de Odontologia de Piracicaba (FOP). Universidade Estadual de Campinas (UNICAMP). Piracicaba , SP, Brazil
• Institution abroad: University of Oslo (UiO), Norway
• Associated to the scholarship: 24/14419-8 - Effect of continuous exposure to chlorhexidine digluconate on competence and genetic transformation of Streptococcus mutans, BP.IC

Abstract

Streptococcus mutans is a naturally competent microorganism, meaning it has the ability to capture and incorporate extracellular DNA into its genome, a capability known as bacterial transformation. Competence is modulated by the expression of the sigma factor gene (sigX), which is activated by peptides such as CSP (competence-stimulating peptide) and XIP (sigX-inducing peptide). Sub-inhibitory concentrations of antimicrobials are stress factors that modulate these pathways, either increasing or decreasing competence capability. The objective of this study will be to evaluate the effect of continuous exposure to chlorhexidine digluconate (CHX) for 1, 7, and 14 days on competence activation and genetic transformation of S. mutans strains. Isogenic mutants of S. mutans containing a luciferase reporter in the promoter regions of the cipB (CSP activation) and sigX (XIP activation) genes will be used. Cultures will be evaluated after 1, 7, and 14 days of continuous exposure to CHX. Culture stocks will be prepared and frozen at optical density (OD600) 0.5. The cultures will then be diluted (1:10) and distributed in 96-well plates, followed by the addition of 1 mM D-luciferin, 250 nM CSP or 1 ¿M XIP, and increasing CHX concentrations (0, 0.25, 0.50, 1.0 ¿g CHX/mL). The plates will be incubated at 37 °C for 12 h in a multidetection microplate reader, during which growth (OD600) and cipB or sigX expression (luminescence) will be measured every 30 min. Luminescence data will be normalized by OD600 values and the area under the curve (AUC) calculated. Samples from the cultures will be evaluated by transmission electron microscopy. Data will be analyzed using one-way ANOVA and Tukey's test (¿ = 5%).