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Published on: February 19, 2019
Effect of filaggrin breakdown products on growth of and protein expression by Staphylococcus aureus
Helen Miajlovic1, Padraic G Fallon, Alan D Irvine
1Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland.
Background:
Colonization of the skin by Staphylococcus aureus in individuals with atopic dermatitis exacerbates inflammation. Atopic dermatitis is associated with loss-of-function mutations in the filaggrin (FLG) gene, accompanied by reduced levels of filaggrin breakdown products on the skin.
Objective:
To assess the affect of growth in the presence of the filaggrin breakdown products urocanic acid (UCA) and pyrrolidone carboxylic acid (PCA) on fitness of and protein expression by S aureus.
Methods:
S aureus was grown for 24 hours in the presence of UCA and PCA, and the density of the cultures was monitored by recording OD(600) values. Cell wall extracts and secreted proteins of S aureus were isolated and analyzed by SDS-PAGE. Cell wall-associated proteins known to be involved in colonization and immune evasion including clumping factor B, fibronectin binding proteins, protein A, iron-regulated surface determinant A, and the serine-aspartate repeat proteins were examined by Western immunoblotting.
Results:
Acidification of growth media caused by the presence of UCA and PCA resulted in reduced growth rates and reduced final cell density of S aureus. At the lower pH, reduced expression of secreted and cell wall-associated proteins, including proteins involved in colonization (clumping factor B, fibronectin binding protein A) and immune evasion (protein A), was observed. Decreased expression of iron-regulated surface determinant A due to growth with filaggrin breakdown products appeared to be independent of the decreased pH.
Conclusion:
S aureus grown under mildly acidic conditions such as those observed on healthy skin expresses reduced levels of proteins that are known to be involved in immune evasion.
Insights
Staphylococcus aureus growth is reduced by filaggrin breakdown products found on healthy skin. These products decrease S. aureus expression of proteins crucial for colonization and immune evasion.
Area of Science:
- Microbiology
- Dermatology
- Biochemistry
Background:
- Atopic dermatitis is linked to Staphylococcus aureus skin colonization, which worsens inflammation.
- Filaggrin (FLG) gene mutations in atopic dermatitis reduce skin filaggrin breakdown products.
Purpose of the Study:
- To determine how urocanic acid (UCA) and pyrrolidone carboxylic acid (PCA) affect Staphylococcus aureus growth and protein expression.
- Investigate the impact of filaggrin breakdown products on S. aureus fitness.
Main Methods:
- S. aureus cultures were grown with UCA and PCA, monitoring optical density (OD600).
- Proteins from cell walls and secreted fractions were analyzed using SDS-PAGE and Western immunoblotting.
- Specific proteins involved in colonization and immune evasion were examined.
Main Results:
- UCA and PCA lowered S. aureus growth rates and final cell density due to media acidification.
- Reduced expression of secreted and cell wall proteins, including clumping factor B and protein A, was observed at lower pH.
- Decreased expression of iron-regulated surface determinant A was independent of pH.
Conclusions:
- Mildly acidic conditions, similar to healthy skin, reduce S. aureus expression of immune evasion proteins.
- Filaggrin breakdown products may influence S. aureus virulence factors on the skin.
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