A Staphylococcus epidermidis strain inhibits the uptake of Staphylococcus aureus derived from atopic dermatitis skin into the keratinocytes.

BACKGROUND: Various bacterial species form a microbiome in the skin. In the past, dead Staphylococcus aureus derived from atopic dermatitis (AD) are taken up by keratinocytes; however, whether live S. aureus can be taken up by keratinocytes is unknown. OBJECTIVE: This study aimed to examine whether live AD strains of S. aureus internalize into the keratinocytes and how the internalization changes under conditions in which other bacterial species including S. epidermidis are present. METHODS: HaCaT cells were cultured with live S. aureus and S. epidermidis (live or heat-treated) or their culture supernatants. After coculture, the change in the amount of S. aureus in the cytoplasm of HaCaT cells was analyzed using, a high-throughput imaging system, Opera Phenix™. RESULTS: Live S. aureus were taken up in the cytoplasm of HaCaT cells. Coculturing live S. aureus with live S. epidermidis or the culture supernatants decreased the abundance of S. aureus in the cytoplasm. The heat-treated culture supernatants of live S. epidermidis or culture supernatants of other S. strains did not decrease the abundance of S. aureus in the cytoplasm. CONCLUSION: Live S. aureus was internalized into the cytoplasm of HaCaT cells as does heat-treated S. aureus. In addition, the heat-sensitive substances secreted by coculture with S. epidermidis and keratinocytes inhibited the uptake of S. aureus by keratinocytes.

Uptake of Staphylococcus aureus by keratinocytes is reduced by interferon-fibronectin pathway and filaggrin expression.

Staphylococcus aureus (S. aureus) is frequently detected in the skin of patients with atopic dermatitis (AD). AD skin-derived strains of S. aureus (AD strain) are selectively internalized into keratinocytes (HaCaT cells) compared to standard strains. However, the mechanism of AD strain internalization by keratinocytes and effect of the skin environment on internalization remain unclear. HaCaT cells were exposed to heat-killed AD or standard strains of fluorescently labeled S. aureus, with or without interferon (IFN)-γ, interleukin (IL)-4, and IL-13 cytokines, for 24 h. Filaggrin and fibronectin expression in HaCaT cells was knocked down using small interfering RNA. The amount of internalized S. aureus was evaluated using a cell imaging system. The effects of INF-γ, IL-4, and S. aureus exposure on mRNA expression in HaCaT cells were analyzed using single-cell RNA sequencing. AD strains adhered to HaCaT cells in approximately 15 min and were increasingly internalized for up to 3 h (2361 ± 467 spots/100 cells, mean ± SD), whereas the standard strain was not (991 ± 71 spots/100 cells). In the presence of IFN-γ, both the number of internalized strains and fibronectin expression significantly decreased compared to in the control, whereas Th2 cytokines had no significant effects. The number of internalized AD strains was significantly higher in filaggrin knockdown and lower in fibronectin knockdown HaCaT cells compared to in the control. RNA sequencing revealed that IFN-γ decreased both fibronectin and filaggrin expression. Keratinocyte internalization of the AD strain may be predominantly mediated by the INF-γ-fibronectin pathway and partially regulated by filaggrin expression.

Staphylococcus aureus in atopic dermatitis: Strain-specific cell wall proteins and skin immunity.

Atopic dermatitis (AD) is a common chronic skin disease. The presence of the bacterium Staphylococcus aureus (S. aureus) is frequently detected on skin affected with AD. In this review, we focused on the characteristics of S. aureus strains isolated from AD skin, particularly the proteins on the cell surface that modulates the interactions between Langerhans cell, keratinocyte, and S. aureus. The skin microbiome plays an important role in maintaining homeostasis of the skin, and colonization of S. aureus in AD is considered to be deeply involved in the clinical manifestation and pathogenesis of skin flares. Colonizing S. aureus strains in AD harbor different surface proteins at the strain level, which are indicated as clonal complexes. Moreover, the cell wall proteins of S. aureus affect skin adhesion and induce altered immune responses. S. aureus from AD skin (AD strain) exhibits internalization into keratinocytes and induces imbalanced Th1/Th2 adaptive immune responses via Langerhans cells. AD strain-derived cell wall proteins and secreted virulence factors are expected to represent therapeutic targets. In addition, the microbiome on the AD skin surface is associated with skin immunity; thus, microbiome-based immunotherapy, whose mechanism of action completely differs from that of typical steroid ointments, are expected to be developed in the future.