Competition between fluoride-resistant and fluoride-sensitive Streptococcus mutans in rat dental plaque

Area of Science:

• Microbiology
• Dental Research
• Fluoride Toxicology

Background:

• Streptococcus mutans (S. mutans) is a primary etiological agent of dental caries.
• Fluoride is widely used for caries prevention, but its effects on S. mutans strain competition are complex.
• The emergence of fluoride-resistant S. mutans strains is a potential concern for oral health.

Purpose of the Study:

• To investigate the impact of fluoride on the competitive dynamics between a fluoride-sensitive S. mutans strain (C180-2) and a fluoride-resistant mutant (C180-2FR) in a rat dental plaque model.
• To determine if fluoride confers a competitive advantage to resistant S. mutans strains under varying conditions.

Main Methods:

• Induction of competition by superinfecting rats or co-caging infected and non-infected rats.
• Administration of sodium fluoride (NaF) via diet, drinking water (60 ppm F), daily 1% F solution brushings, or combined methods.
• Analysis of S. mutans strain colonization and competition in rat dental plaque.

Main Results:

• Fluoride applications generally favored the fluoride-resistant S. mutans C180-2FR strain.
• Fluoride protected plaque harboring the resistant strain against colonization by the sensitive parent strain.
• The resistant strain successfully colonized plaque in naive rats under combined fluoride treatments, but not in pre-colonized plaque.

Conclusions:

• Fluoride pressure can provide an ecological advantage to fluoride-resistant S. mutans mutants.
• While fluoride can promote the establishment of resistant strains, it does not ensure their dominance over established sensitive strains.
• Findings suggest potential implications for human dental plaque colonization by resistant S. mutans strains under therapeutic fluoride use.