Proteolytic activity of Staphylococcus aureus strains isolated from the colonized skin of patients with acute-phase atopic dermatitis

Abstract

Staphylococcus aureus strains isolated from the colonized skin lesions of 26 patients with acute-phase atopic dermatitis were reported to produce various extracellular proteolytic enzymes. Using the skim-milk-agar culture plating method, it was shown that 97% of the strains (65 of 67 examined) produced proteolytic activity, with 61% (42 strains) producing activity comparable to that of the proteolytically hyperactive reference strain Staphylococcus aureus V8. This observation was confirmed by azocasein degradation with culture supernatants, which indicated that 91% of the strains produced extracellular proteinases and 43% exceeded the 2% activity threshold of the reference strain. Control strains were isolated from the nose vestibules of 18 healthy carriers; the proteolytic activity of these strains never exceeded 2.5% of the activity of the reference strain. In 54% of the patients examined (n=14), the activity of the strains was higher than that determined for the isolates from the control group. The combined use of assays incorporating azocasein and a synthetic chromogenic substrate, N-CBZ-Phe-Leu-Glu-pNA, showed that two staphylococcal enzymes, Staphylococcus aureus metalloproteinase (SAMP) and Staphylococcus aureus serine proteinase (SASP), contributed to the total proteolytic activity released by the strains examined. The contribution of each of the two enzymes varied greatly between different isolates. The undamaged skin of the patients was not colonized with Staphylococcus aureus. The presence of several strains with atypical proteinase characteristics was also reported, suggesting the possible involvement of enzymes other than serine- and metalloproteinases in the proteolytic activity of Staphylococcus aureus. Taken together, the results of the study imply that staphylococcal proteinases may contribute to the pathogenicity of atopic dermatitis.