Tolerance and Persister Formation in Oral Streptococci

Area of Science:

• Microbiology
• Dental Science
• Antimicrobial Resistance

Background:

• Oral streptococci are key players in dental plaque formation and infections.
• Chlorhexidine is a widely used antiseptic in dentistry.
• Subinhibitory concentrations of antimicrobials can lead to the development of microbial tolerance.

Purpose of the Study:

• To investigate if long-term exposure to subinhibitory chlorhexidine concentrations influences the emergence of tolerant or persistent cells in oral streptococci.
• To determine if previously exposed oral streptococci exhibit increased tolerance to high chlorhexidine concentrations.

Main Methods:

• Two oral streptococcal strains, *S. mutans* and *S. sobrinus*, were exposed to subinhibitory concentrations of chlorhexidine over an extended period.
• Following exposure, bacterial cultures were incubated in media with high chlorhexidine concentrations.
• The emergence of tolerant and persistent cell subpopulations was assessed by comparing growth and survival rates.

Main Results:

• A distinct subpopulation of chlorhexidine-tolerant cells emerged in streptococci previously exposed to subinhibitory chlorhexidine.
• Control strains, not exposed to subinhibitory concentrations, did not show this increased tolerance.
• These findings suggest that prior low-level exposure can select for more resilient bacterial cells.

Conclusions:

• Long-term exposure to subinhibitory chlorhexidine can induce tolerance and persistence in oral streptococci.
• These tolerant subpopulations may develop *in vivo*, posing challenges for infection control.
• Rational and appropriate use of antimicrobials, particularly in long-term dental applications, is critical to mitigate resistance and tolerance development.