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Human skin is covered with bacteria, especially Staphylococcus epidermidis. For the most part, these bacteria live on us in peace. The colonization has traditionally been considered to be beneficial in crowding out more pathogenic bacteria, such as S. aureus, but the mechanism may not be that simple.
Investigators have discovered that, in vitro, a small (<10 kDa), nontoxic molecule elaborated by S. epidermidis enhanced the mRNA expression of human β-defensins (HBDs) 2 and 3 in undifferentiated keratinocytes. This upregulation was associated with increased capacity of cell lysates to inhibit the growth of pathogenic bacteria, including S. aureus and group A streptococci. In mice, these effects seemed to be mediated by Toll-like receptor-2: A …