Effect of filaggrin breakdown products on growth of and protein expression by Staphylococcus aureus

Helen Miajlovic,Padraic G Fallon,Alan D Irvine,Timothy J Foster

doi:10.1016/j.jaci.2010.09.015

Abstract

BackgroundColonization 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.ObjectiveTo 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.MethodsS aureus was grown for 24 hours in the presence of UCA and PCA, and the density of the cultures was monitored by recording OD600 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.ResultsAcidification 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.ConclusionS 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.

Highlights

Colonization of the skin by Staphylococcus aureus in individuals with atopic dermatitis exacerbates inflammation
S aureus strain SH1000 was used in this study because it expresses the majority of surface-associated proteins involved in colonization
Growth in the presence of urocanic acid (UCA) and pyrrolidone carboxylic acid (PCA) resulted in an increased doubling time (49 minutes), and the final yield of cells was reduced by 38% (OD600 nm, 3.7.) Neutralizing the pH after addition of UCA and PCA resulted in growth rates and cell densities (OD600 nm, 5.7) similar to those seen when SH1000 was grown in tryptone soy broth (TSB)

Summary

Introduction

Colonization of the skin by Staphylococcus aureus in individuals with atopic dermatitis exacerbates inflammation. 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. 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. 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. 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. 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. (J Allergy Clin Immunol 2010;126:1184-90.)

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