Introduction

The genus Staphylococcus represents a diverse group of Gram-positive bacteria that are integral components of the human microbiome. While often discussed in the context of opportunistic infections, many staphylococcal species act as essential commensals that help maintain the structural and immunological integrity of various body sites. Understanding the balance between these beneficial commensals and potential pathobionts is key to managing overall microbial diversity and preventing the onset of dysbiosis.

Location of the Microbe

Skin

Staphylococcus is a dominant genus across various skin niches, including dry, moist, and sebaceous areas. It is frequently detected in the axilla, extremities, and facial skin, where it interacts with other commensals like Cutibacterium to shape the cutaneous ecosystem.

Nasal

The nasal cavity serves as a primary colonization site for Staphylococcus. It is a critical niche where species like S. lugdunensis and S. aureus compete for dominance, influencing the overall resilience of the respiratory tract microbiome.

Oral

In the oral cavity, Staphylococcus exists as part of a complex community. While typically less dominant than in skin or nasal sites, it can be detected in saliva and the oropharynx, particularly in critically ill patients or those with specific oral health conditions.

Behavior During Dysbiosis

Skin

In the skin, dysbiosis is often characterized by a loss of microbial diversity and the overabundance of S. aureus. This shift is associated with the breakdown of the epidermal barrier and the suppression of beneficial commensals, creating a self-sustaining inflammatory loop.

Nasal

Nasal dysbiosis involves the displacement of protective commensals by pathobionts. An increase in S. aureus abundance, often coinciding with a decrease in S. lugdunensis, can increase the risk of subsequent respiratory or systemic infections.

Oral

Oral dysbiosis may manifest as a shift toward biofilm-forming bacteria. In severely ill patients, an increase in Gram-positive bacteria, including Staphylococcus, is associated with a more vulnerable community structure and decreased modularity.

Disease Associations

Skin Ecosystem

Atopic Dermatitis (AD)

The overgrowth of S. aureus is strongly associated with the pathogenesis of Atopic Dermatitis. Pathogenic strains utilize the Agr quorum-sensing system to express toxins that exacerbate type 2 inflammation and impair gut barrier integrity. Colonization in early life with such strains is associated with an increased risk of developing AD.

Psoriasis

Cutaneous dysbiosis featuring S. aureus dominance is associated with psoriatic lesions. These bacteria produce proteases that degrade corneodesmosomes, impairing epidermal cohesion and triggering the IL-23/Th17 inflammatory axis.

Actinic Keratosis (AK) and SCC

An overabundance of Staphylococcus is a feature of AK and squamous cell carcinoma (SCC). S. aureus may promote tumor progression by stimulating the production of beta-defensins, which can increase keratinocyte proliferation.

Chronic Wounds and Diabetic Foot Ulcers (DFUs)

S. aureus is highly prevalent (up to 70%) in hard-to-heal wounds. Its presence, often in biofilms, is associated with increased infection severity and prolonged treatment duration.

Nasal Ecosystem

Chronic Maxillary Sinusitis

S. lugdunensis has been identified as a potential etiological factor in chronic maxillary sinusitis. Its ability to produce biofilms allows it to persist in the sinuses, contributing to the chronicity of the disease.

Respiratory Infections

Nasal carriage of S. aureus serves as a reservoir for subsequent invasive infections. In the context of COVID-19, the prominence of Staphylococcus in the lower respiratory tract is associated with increased disease severity in intubated patients.

Oral Ecosystem

Severe Early Childhood Caries

Spearman correlation analyses have associated the presence of Staphylococcus in saliva with altered metabolic profiles in children with severe dental caries.

ICU-Acquired Infections

In critically ill patients, a significant increase in S. aureus (including MRSA) within the oropharyngeal microbiota is associated with severe dysbiosis and poor clinical outcomes.

Foods Supporting Healthy Balance

Dietary patterns significantly influence the systemic environment that supports a balanced microbiome. A high-fiber, low-fat diet is associated with a reduction in the abundance of antimicrobial resistance (AMR) genes within pathogenic genera, including Staphylococcus. Fiber-rich foods support the growth of SCFA-producing bacteria, which help maintain the integrity of the gut barrier, thereby reducing the risk of microbial translocation into the bloodstream.

Additionally, the intake of flavonoids, specifically anthocyanidins and flavanones found in red fruits and citrus, has been linked to a reduction in the prevalence of Staphylococcus in blood bacterial DNA, suggesting a protective effect on intestinal permeability. For infants, exclusive breastfeeding (mothers' own milk) promotes the colonization of beneficial staphylococcal species while reducing the abundance of potentially inflammatory Proteobacteria, supporting early immune development.

Actionable Insights

• Prioritize Fiber Intake: Transitioning to a high-fiber, low-fat diet may help reduce the burden of antimicrobial resistance genes associated with staphylococcal populations.
• Support Skin Barrier Health: The use of early emollients in high-risk infants can reduce the abundance of S. aureus and S. epidermidis, potentially delaying the onset of atopic dermatitis.
• Consider Probiotic Support: Certain probiotic mixtures, such as those containing Lactobacillus rhamnosus or B. subtilis, have demonstrated the potential to competitively inhibit S. aureus colonization.
• Nasal Hygiene: Since the nasal cavity acts as a reservoir for S. aureus, maintaining nasal hygiene and monitoring for colonization can be a preventive measure for respiratory health.
• Breastfeeding: Encourage exclusive breastfeeding in neonates to foster a healthy early-life microbiome and support metabolic homeostasis.

Conclusion

Staphylococcus is a complex genus whose impact on human health depends heavily on the specific strain and the ecological niche it occupies. In a state of balance, commensal staphylococci such as S. epidermidis and S. lugdunensis provide essential colonization resistance and immune modulation. However, in the presence of barrier defects or immune dysregulation, the ecosystem can shift toward an overabundance of S. aureus, which is associated with a range of inflammatory and infectious conditions across the skin, nasal, and oral environments. Managing this balance through diet, skincare, and targeted probiotics represents a promising path toward preventive health.

Commensal Staphylococci attenuate Staphylococcus aureus skin colonization and inflammation via AHR-dependent signaling

Psoriasis: microbiome dysbiosis and pathogenic mechanisms

Comparative analysis of the postadmission and antemortem oropharyngeal and rectal swab microbiota of ICU patients

Dysbiosis in the Pathogenesis of Atopic Dermatitis