Cell density modulates acid adaptation in Streptococcus mutans: implications for survival in biofilms

Area of Science:

• Microbiology
• Oral Health
• Bacterial Physiology

Background:

• Streptococcus mutans colonizes dental biofilms and endures acidic conditions from dietary carbohydrates.
• Acid survival is a critical virulence factor in dental caries pathogenesis.
• Limited research exists on acid adaptation in high-cell-density S. mutans biofilms.

Purpose of the Study:

• To investigate the acid tolerance response (ATR) of S. mutans biofilm cells.
• To determine how cell density influences the induction of acid adaptation in S. mutans.
• To explore the role of quorum sensing in S. mutans acid adaptation.

Main Methods:

• S. mutans BM71 grown in broth and chemostat biofilm fermentors.
• Acid adaptation assessed via low pH (pH 3.5) exposure.
• Survival rates of biofilm and planktonic cells quantified.
• Analysis of quorum sensing mutants (comC, comD, comE) and competence stimulating peptide (CSP).

Main Results:

• S. mutans exhibits log-phase ATR induced by low pH and stationary-phase resistance via carbon starvation.
• Higher cell density and dense biofilms significantly increase S. mutans acid resistance.
• Extracellular factors in culture filtrate induce ATR; quorum sensing mutants show diminished ATR, restored by CSP.

Conclusions:

• Cell density and biofilm growth modulate S. mutans acid adaptation.
• Optimal acid adaptation involves both low pH induction and cell-cell communication via quorum sensing.
• Findings provide insights into S. mutans virulence in dental caries.