Dextran-induced aggregation in a mutant of Streptococcus sobrinus 6715-13

Area of Science:

• Microbiology
• Oral Health Research
• Biochemistry

Background:

• Streptococcus sobrinus plays a key role in dental caries formation.
• Bacterial aggregation and plaque formation are critical steps in cariogenesis.
• Previous studies identified Streptococcus sobrinus mutants with altered aggregation or plaque formation.

Purpose of the Study:

• To characterize a novel Streptococcus sobrinus mutant resistant to dextran-induced aggregation.
• To investigate the roles of dextranase and glucosyltransferase in bacterial aggregation and plaque formation.
• To elucidate the mechanisms underlying dextran-mediated aggregation in Streptococcus sobrinus.

Main Methods:

• Isolation and characterization of a Streptococcus sobrinus mutant resistant to exogenous dextran.
• In vitro assays measuring plaque formation in the presence of sucrose.
• Enzymatic activity assays (glucosyltransferase, dextranase) and analysis of glucose incorporation into glucan.
• Thermal stability studies of catalytic and receptor functions.
• Binding assays for labeled dextrans to bacterial cells.
• Immunological cross-reactivity studies using anti-sera against glucosyltransferase and dextranase.

Main Results:

• A mutant Streptococcus sobrinus strain was isolated that resists dextran aggregation but forms adherent plaque in vitro.
• This variant possesses dextranase activity, complementing previously studied isolates.
• Evidence suggests that neither dextranase nor glucosyltransferase directly acts as the receptor for dextran-induced aggregation.
• Anti-glucosyltransferase and anti-dextranase sera blocked bacterial aggregation, indicating antigenic cross-reactivity related to alpha(1-6) glucan linkages.
• A model proposes that enzymatic function precedes dextran receptor activity during cell emergence.

Conclusions:

• Dextran-induced aggregation in Streptococcus sobrinus involves distinct receptors separate from the primary enzymatic functions of glucosyltransferase and dextranase.
• Antigenic similarities between these enzymes suggest a shared evolutionary or structural basis for recognizing glucan structures.
• The findings provide insights into the complex mechanisms of bacterial adhesion and plaque formation relevant to oral microbiology.