Introduction

Streptococcus australis is a member of the diverse streptococcal group found within the human microbiome. Primarily recognized as a commensal inhabitant of the oral cavity, this microbe plays a nuanced role in maintaining the balance of the gut-oral axis and respiratory niches. Understanding its functional potential is key to grasping how certain bacteria can be associated with health-promoting outcomes, particularly in the prevention of dental caries and the maintenance of mucosal integrity.

Location of Microbe

Oral Ecosystem

In the oral ecosystem, S. australis is commonly found within dental biofilms and saliva, often colonizing sound tooth surfaces where it contributes to the overall microbial diversity of the mouth.

Nasal Ecosystem

Within the nasal ecosystem, this microbe exists as part of the commensal flora, contributing to the protective microbial barrier of the upper respiratory tract.

Respiratory Ecosystem

In the respiratory ecosystem, S. australis can be detected in the lower respiratory tract and associated mucosal surfaces, often mirroring the colonization patterns found in the oral cavity.

Behavior During Dysbiosis

Oral Ecosystem

During oral dysbiosis, S. australis is typically more abundant on sound surfaces rather than those with active white spot lesions, suggesting its presence is associated with a healthier biofilm state.

Nasal Ecosystem

In the nasal niche, shifts in abundance may occur during inflammatory responses, where a loss of commensal diversity can lead to an environment more susceptible to opportunistic pathogens.

Respiratory Ecosystem

Within the respiratory tract, dysbiosis is characterized by a shift in the host-microbe interaction, where the reduction of commensals like S. australis may correlate with increased inflammatory signaling.

Disease Associations

Oral Ecosystem

In the oral ecosystem, Streptococcus australis is predominantly associated with sound tooth surfaces and a lack of active white spot lesions. Unlike cariogenic species such as S. mutans, S. australis is identified as a non-cariogenic species. It is positively associated with Veillonella rogosae, which is considered a biomarker for a non-cariogenic oral microbiome. Furthermore, in patients with severe periodontitis, the presence of S. australis has been associated with therapeutic success, meaning its abundance is higher in individuals who respond well to periodontal therapy compared to those with refractory periodontitis.

Nasal and Respiratory Ecosystems

In the nasal and respiratory ecosystems, S. australis generally functions as a commensal. While specific disease-causing roles are not highlighted, its absence or displacement by opportunistic pathogens is often associated with a breakdown in the mucosal barrier, which may increase susceptibility to upper respiratory tract infections. Its presence typically reflects a stable, balanced microbial community within these niches.

Foods Supporting Healthy Balance

Maintaining a healthy abundance of beneficial streptococci like S. australis involves managing the oral and systemic environment to prevent the overgrowth of acid-producing bacteria. Reducing the frequency of fermentable carbohydrates (such as sugary snacks and soft drinks) between meals is critical, as high carbohydrate consumption is associated with reduced bacterial diversity and a shift toward cariogenic species. Incorporating a diet rich in fiber and prebiotic-rich vegetables can support a diverse microbial ecosystem. Additionally, foods that promote a neutral or slightly alkaline salivary pH may help inhibit the growth of caries-initiators while supporting the survival of arginolytic and commensal species like S. australis. Proper hydration and the consumption of water help clear sugars and maintain the gut barrier integrity through systemic health.

Actionable Insights

Oral Health Management

• Reduce intake of fermentable carbohydrates to prevent dysbiosis and support the prevalence of non-cariogenic bacteria like S. australis.
• Maintain regular dental hygiene to support a diverse biofilm, as higher microbial diversity is associated with sound tooth surfaces.
• Consult with a provider about the potential of arginolytic probiotics to inhibit the growth of dental plaque.

Nasal and Respiratory Care

• Practice gentle nasal hygiene to maintain the commensal microbial balance of the nasal ecosystem.
• Ensure adequate humidity in living spaces to protect the respiratory mucosal barrier and support commensal host-microbe interactions.

General Wellness

• Prioritize a balanced diet to support the enteromammary route and general microbiome health, which can influence microbial distribution across different niches.

Conclusion

The impact of Streptococcus australis on human health is highly dependent on its strain and the specific niche context in which it resides. In the oral ecosystem, it serves as a protective commensal associated with sound tooth surfaces and successful periodontal recovery. In the nasal and respiratory ecosystems, it contributes to the baseline microbial diversity necessary for mucosal health. By focusing on the reduction of fermentable sugars and maintaining overall microbial diversity, individuals can support the presence of such beneficial species, promoting a balanced ecosystem and reducing the risk of dysbiosis across multiple biological sites.