Relationship between cell-bound dextransucrase and the agglutination of Streptococcus mutans

Area of Science:

• Microbiology
• Oral Health
• Biochemistry

Background:

• Streptococcus mutans is a key bacterium in dental caries development.
• Bacterial cell agglutination is a significant factor in biofilm formation.
• The role of dextran and cell surface interactions in S. mutans agglutination requires clarification.

Purpose of the Study:

• To investigate the relationship between dextransucrase activity and dextran-induced agglutination in Streptococcus mutans.
• To determine the influence of cell treatments and metal ions on bacterial agglutination.
• To elucidate the mechanism of dextran-mediated cell aggregation in S. mutans.

Main Methods:

• Enzymatic and chemical treatments to modify cell-bound dextransucrase activity.
• Induction of cell agglutination using dextrans of varying structures and molecular weights.
• Assessment of agglutination in the presence and absence of divalent metal ions, including calcium.
• Treatment of cells with enzymes (trypsin) and chelating agents (EDTA).

Main Results:

• Dextran-induced agglutination of S. mutans is independent of cell-bound dextransucrase activity.
• Treatments that abolish dextransucrase activity (e.g., toluene, Hg2+, Cu2+, heat) do not inhibit dextran-induced agglutination.
• Branched dextrans are more effective inducers of agglutination than linear dextrans of similar molecular weight.
• Divalent metal ions are essential for agglutination; heat- or EDTA-treated cells specifically require Ca2+.

Conclusions:

• The agglutination mechanism of Streptococcus mutans by dextrans is primarily mediated by cell surface receptors, not dextransucrase activity.
• Calcium ions play a critical role in facilitating S. mutans cell agglutination, potentially by activating receptors or forming bridges.
• Dextran structure, specifically branching, influences its efficacy in inducing bacterial cell aggregation.