Streptococcus mutans dextransucrase: stimulation by phospholipids from human sera and oral fluids

Area of Science:

• Microbiology
• Biochemistry
• Oral Biology

Background:

• Streptococcus mutans is a primary etiological agent in dental caries.
• Dextransucrase (EC 2.4.1.5) from S. mutans synthesizes glucans, contributing to biofilm formation and cariogenicity.
• Oral fluids contain various components that may influence bacterial enzyme activity.

Purpose of the Study:

• To investigate the effect of human oral fluids on Streptococcus mutans dextransucrase activity.
• To determine if phospholipids in oral fluids stimulate glucan formation.
• To assess the role of oral fluid components in the cariogenic potential of S. mutans.

Main Methods:

• Collected serum, gingival crevicular fluid, and parotid, submandibular, and labial saliva from four individuals.
• Assayed dextransucrase activity using crude enzyme preparations and purified enzyme forms in the presence of oral fluids.
• Investigated the role of lysophosphatidylcholine (LPC) by comparing stimulation from purified oral fluid LPC and egg yolk LPC.

Main Results:

• All tested oral fluids significantly stimulated glucan formation by crude dextransucrase (approx. 1.8-fold) and purified enzyme forms (water-insoluble: approx. 3.2-fold; water-soluble: approx. 2.4-fold).
• Stimulatory effects were potent, requiring dilutions greater than 1:1,000 to become undetectable.
• Lysophosphatidylcholine purified from oral fluids stimulated dextransucrase as effectively as egg yolk LPC, indicating phospholipids enhance enzyme activity.

Conclusions:

• Human oral fluids contain potent stimulators of Streptococcus mutans dextransucrase activity.
• Phospholipids present in oral fluids play a key role in enhancing dextransucrase function.
• These findings suggest a mechanism by which oral fluid components may contribute to the cariogenic potential of S. mutans.