Introduction

Actinomycetota (formerly known as Actinobacteria) represents a diverse phylum of Gram-positive bacteria that serve as integral components of the human microbiome. These microorganisms are widely distributed across various anatomical sites, most notably within the oral cavity and on the skin, where they contribute to the overall microbial diversity and stability of the host's ecosystems. By engaging in complex host-microbe interactions, Actinomycetota help maintain the balance of these niches, though their role can shift significantly during states of dysbiosis.

Location of Microbe

Oral Ecosystem

In the oral cavity, Actinomycetota are prevalent across multiple niches, including supragingival plaque, saliva, and the tongue. Specifically, the genus Actinomyces is a common resident of the subgingival microbiome, where it typically functions as a commensal member of the community.

Skin Ecosystem

Actinomycetota are among the most prevalent and diverse phyla found on healthy human skin. They contribute to the baseline microbial landscape, though their abundance can be significantly altered in diseased skin, such as in psoriatic lesions.

Behavior During Dysbiosis

Oral Ecosystem

In the oral environment, dysbiosis is characterized by a significant reduction in the relative abundance of Actinomycetota, particularly the genus Actinomyces. This depletion is notably observed in patients with type 2 diabetes mellitus (T2DM), where the diabetic microenvironment exerts selective pressure that favors the expansion of other groups while reducing these commensals.

Skin Ecosystem

Cutaneous dysbiosis involves a marked underrepresentation of Actinomycetota in psoriatic lesions compared to uninvolved skin or healthy controls. This shift is often accompanied by an increase in the phylum Firmicutes, contributing to a loss of the protective microbial balance and promoting a pro-inflammatory state.

Disease Associations

Oral Ecosystem Associations

Within the oral niche, Actinomycetota are associated with the progression of periodontal disease and systemic metabolic conditions. In patients with severe periodontitis and well-controlled type 2 diabetes mellitus (T2DM), there is a significant reduction in the phylum Actinomycetota, specifically the genus Actinomyces. This reduction is linked to the altered nutrient profile of the gingival crevicular fluid in diabetic patients, which may favor the growth of 'inflammophilic' bacteria over commensal Actinomycetota. Furthermore, oral dysbiosis is associated with the systemic onset of rheumatoid arthritis (RA), where the imbalance of oral microbiota may act as a trigger for systemic autoimmune responses and the generation of anti-citrullinated protein antibodies (ACPAs).

Skin Ecosystem Associations

In the skin ecosystem, a depletion of Actinomycetota is strongly associated with psoriatic lesions. Healthy skin is typically characterized by a high prevalence of this phylum, but in psoriasis, they are significantly underrepresented. This loss of microbial balance is associated with the disruption of the local barrier and the amplification of the IL-23/Th17 inflammatory axis. Additionally, alterations in the gut microbiome—which can include shifts in Actinomycetota-related abundances—are associated with the active spreading phase of vitiligo, an autoimmune skin disease, suggesting a complex gut-skin axis interaction that drives systemic inflammation and melanocyte destruction.

Foods Supporting Healthy Balance

Maintaining a diverse and balanced microbiome across the oral and skin ecosystems is closely linked to dietary patterns that reduce systemic inflammation and support gut barrier integrity. A Mediterranean-style diet—rich in whole grains, legumes, nuts, fruits, vegetables, and olive oil—is associated with lower levels of circulating advanced glycation end products (AGEs) and reduced oxidative stress, which helps prevent the systemic inflammation that can trigger dysbiosis in distal niches like the skin and mouth.

The consumption of fermented foods, such as kefir, kimchi, and yogurt, introduces beneficial probiotics like Lactobacillus and Bifidobacteria. These microbes can influence brain health and systemic immunity, potentially mitigating the inflammatory triggers that lead to skin and oral imbalances. Furthermore, a high intake of dietary fibers and prebiotics (such as those found in seaweeds and microalgae) promotes the production of short-chain fatty acids (SCFAs). SCFAs are critical for maintaining the gut ecosystem and reducing the translocation of pro-inflammatory markers, which in turn protects the skin and oral mucosal surfaces from exaggerated immune responses.

Actionable Insights

• Prioritize Fiber-Rich Diets: Focus on whole grains and legumes to support the production of SCFAs, which help regulate systemic inflammatory signaling and maintain the integrity of mucosal barriers.
• Incorporate Fermented Foods: Regularly consume probiotic-rich foods to support a diverse microbial community, which is associated with better immune regulation and mental well-being.
• Limit Ultra-Processed Foods: Reduce the intake of foods high in added sugars and saturated fats, as these are linked to the production of glycotoxins and a higher risk of systemic dysbiosis.
• Maintain Oral Hygiene: Practice consistent oral care to prevent the overgrowth of pathogens and protect commensal populations like Actinomyces, especially for individuals with metabolic conditions such as diabetes.
• Support Skin Health: Utilize antioxidants from a variety of colorful vegetables and fruits to counteract the oxidative stress that often accompanies the depletion of protective skin microbes.

Conclusion

Actinomycetota plays a vital role as a commensal stabilizer in both the oral and skin ecosystems. Its presence is typically associated with health and barrier stability, while its depletion is often a marker of dysbiosis in conditions such as psoriasis and diabetic periodontitis. Because these microbes are linked to the broader gut-skin axis and systemic inflammatory pathways, maintaining a balanced microbiome requires a holistic approach. The impact of Actinomycetota depends heavily on the specific niche context and the overall microbial balance; therefore, fostering a high-diversity ecosystem through nutrition and hygiene is key to preventing the transition from commensalism to disease-associated dysbiosis.