Biology of Oral Streptococci Original paper

What was reviewed?

This paper is a comprehensive review of the biology of oral streptococci, focusing on their ecological roles, metabolic traits, and interactions within the oral microbiome and with the human host. The authors synthesized microbiological, genetic, and clinical evidence to explain how oral streptococci function as early colonizers of the oral cavity, organizers of dental biofilms, and key modulators of oral health and disease. The review framed oral streptococci not as a single functional group but as a diverse collection of species whose behavior depends on niche, community context, and host factors.

Who was reviewed?

The review drew on studies involving human oral ecosystems across the lifespan, including healthy individuals, children during tooth eruption, and patients with dental caries, periodontal disease, endocarditis, and respiratory complications linked to oral bacteria. It integrated data from saliva, dental plaque, and mucosal surfaces, supported by in vitro biofilm models, genomic analyses, and animal studies. These sources allowed the authors to connect species-level traits with clinically relevant outcomes.

What were the most important findings?

The review established that oral streptococci dominate the early stages of oral biofilm formation and act as ecological gatekeepers for subsequent microbial colonization. Major microbial associations included Streptococcus mitis, Streptococcus sanguinis, Streptococcus gordonii, Streptococcus salivarius, Streptococcus mutans, and Streptococcus sobrinus, each occupying distinct niches on teeth or mucosal surfaces. Health-associated streptococci such as S. mitis, S. sanguinis, and S. gordonii promoted microbial balance by producing hydrogen peroxide, bacteriocins, and alkali-generating enzymes that suppressed acidogenic and pathogenic competitors. These species also interacted closely with host tissues, contributing to immune tolerance and epithelial homeostasis.

In contrast, cariogenic streptococci such as S. mutans displayed specialized adaptations for acid production, acid tolerance, and extracellular polysaccharide synthesis, enabling persistent biofilm growth under low pH conditions. The review highlighted how shifts in carbohydrate availability and salivary flow selectively favored these aciduric species, driving enamel demineralization and caries development. Importantly, oral streptococci were shown to engage in extensive metabolic cross-feeding and signaling with other oral microbes, shaping community structure through adhesion molecules, quorum sensing, and competitive exclusion. Beyond the oral cavity, the authors emphasized that streptococci can translocate or seed distant sites, contributing to infective endocarditis and respiratory infections when host barriers are compromised, underscoring their dual commensal–pathogenic potential.

What are the greatest implications of this review?

For clinicians, this review reinforces that oral streptococci are central regulators of oral ecosystem stability rather than incidental flora. It supports prevention strategies that preserve health-associated streptococcal communities while limiting ecological conditions that favor acidogenic and invasive strains, highlighting the microbiome as a modifiable factor in oral and systemic disease risk.