Staphylococci may play key role in environmental mechanism of Atopic Dermatitis

Recent study data have found that the environmental component of atopic dermatitis may be related to biofilm-producing staphylococci, which obstruct sweat ducts.

In the university hospital-based, dermatologic clinic study, researchers collected tissue samples from 40 patients who presented with AD to the Drexel University College of Medicine Dermatology Clinic in Philadelphia. The study population included 21 males and 19 females aged 3 months to 85 years.

Samples were acquired from lesions, which were not affected by impetigo, in various locations based on the presentation of the AD. In flexural AD, for example, the samples were taken from the antecubitals, and in facial-extensor AD, they were taken from the face. Skin scrapings and biopsy specimens were obtained from the AD lesions, as well as from non-lesional locations. The researchers then assembled microbial cultures using conventional methods. The samples were exposed to Gram’s staining, bright-field microscopy, hematoxylin and eosin, periodic acid–Schiff, Congo red agar, and light microscopy.

Additionally, the researchers collected samples from 20 control patients, including 10 samples of skin inflammation and 10 samples of non-inflamed, non-atopic skin.

The researchers found that in all samples of AD, there were multidrug-resistant staphylococci. The most prevalent species seen wereStaphylococcus aureus(42%) and S. epidermidis (20%). Extracellular polysaccharide and biofilm were found in all isolates (85% strong biofilm producers and 15% moderately to weak biofilm producers). The biofilm-mediating genes icaD and aap were found in the isolates using PCR (93% and 12.5%, respectively); some isolates contained both genes. The skin tissues also were evaluated for microbial identification, extracellular biomass formation, biofilm formation and staphylococcal biofilm.

Upon microscopic tissue analysis, the researchers confirmed occlusion of sweat ducts with periodic acid–Schiff-positive and Congo red-positive agar. Additionally, they found that toll-like receptor 2 was activated in AD lesions proximal to the sweat ducts, which may have triggered proteinase-activated, receptor-2 mediated itching and MyD88-mediated intercellular edema.

The researchers said discussions of possible therapies based on these findings are premature, but oral antibiotics would seem to be a poor choice for these MDR bacteria.

“Topical antibacterial measures, such as bleach baths or bleach gels, seem more reasonable,” the researchers wrote. “While the stratum corneum is compromised, assiduous skin care, including aggressive moisturization, seems appropriate. Further studies are underway.”