Antagonistic interactions by a high H₂ O₂ -producing commensal streptococcus modulate caries development by...

Area of Science:

• Microbiology
• Oral Health
• Bacterial Interactions

Background:

• Dental caries result from polymicrobial biofilms on teeth, with Streptococcus mutans linked to childhood cavities.
• Commensal bacteria can produce antimicrobials like hydrogen peroxide (H2O2) to inhibit S. mutans, but sugar-rich diets disrupt this balance.
• Streptococcus oralis subsp. tigurinus strain J22 is a newly identified, highly potent H2O2 producer.

Purpose of the Study:

• To investigate if a high H2O2-producing commensal streptococcus can alter the spatial organization and virulence of S. mutans within biofilms.
• To assess the efficacy of S. oralis J22 in preventing enamel demineralization and caries development.
• To explore the role of H2O2 production by S. oralis J22 in inhibiting S. mutans growth.

Main Methods:

• Utilized an experimental biofilm model to study S. oralis J22 and S. mutans interactions on ex vivo human tooth surfaces.
• Employed an in vivo rodent caries model under a sugar-rich diet to evaluate coinfection effects.
• Analyzed the H2O2 generation mechanism in S. oralis J22, specifically the role of pyruvate oxidase (SpxB), and its sugar-repression resistance.

Main Results:

• S. oralis J22 significantly inhibited S. mutans clustering, accumulation, and spatial organization in biofilms, reducing enamel demineralization.
• H2O2 generation by S. oralis J22 was not repressed by sugars, leading to enhanced S. mutans growth inhibition compared to S. gordonii.
• Coinfection with S. oralis in the rodent model reduced caries development, unlike coinfection with S. gordonii.

Conclusions:

• Oral bacteria with high H2O2 production capabilities, like S. oralis J22, can modulate biofilm cariogenicity in vivo.
• Bacterial antagonistic interactions within oral polymicrobial communities are crucial for maintaining oral health and preventing disease.
• Harnessing potent H2O2-producing commensals presents a potential therapeutic strategy against dental caries.