A peroxidase-mediated, streptococcus mitis-dependent antimicrobial system in saliva

Area of Science:

• Microbiology
• Oral Biology
• Biochemistry

Background:

• Saliva contains a natural antimicrobial system.
• This system relies on peroxidase enzymes and microbial hydrogen peroxide (H2O2) production.
• Streptococcus mitis is a common oral bacterium.

Purpose of the Study:

• To investigate the H2O2 production by Streptococcus mitis.
• To evaluate the antimicrobial potential of S. mitis-derived H2O2 in conjunction with salivary components.
• To understand the role of this system in host defense.

Main Methods:

• Measured H2O2 formation by S. mitis via [(14)C]formate conversion to (14)CO2.
• Assessed antimicrobial activity using viable cell counts and [(14)C]valine uptake assays.
• Tested systems with lactoperoxidase (LPO), iodide, thiocyanate, and saliva.

Main Results:

• H2O2 production by S. mitis was optimal at pH 6.0-6.5 and required glucose.
• The S. mitis-H2O2 system, with LPO and iodide/thiocyanate, inhibited growth of E. coli, S. aureus, and C. tropicalis.
• Saliva could substitute for LPO and thiocyanate, demonstrating a natural antimicrobial mechanism.

Conclusions:

• Streptococcus mitis contributes to the oral antimicrobial defense through H2O2 production.
• The lactoperoxidase system in saliva, enhanced by microbial H2O2, plays a role in controlling oral pathogens.
• This study highlights a microbial-dependent host defense mechanism in saliva.