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Title: Colonization of epidermal tissue by Staphylococcus aureus produces localized hypoxia and stimulates secretion of antioxidant and caspase-14 proteins

Author
item LONE, ABDUL - Washington State University
item ATCI, ERHAN - Washington State University
item RENSLOW, RYAN - Pacific Northwest National Laboratory
item BEYENAL, HALUK - Washington State University
item Noh, Susan
item FRANSSON, BOEL - Washington State University
item ABU-LAIL, NEHAL - Washington State University
item PARK, JEONG-JIN - Washington State University
item GANG, DAVID - Washington State University
item CALL, DOUGLAS - Washington State University

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2015
Publication Date: 8/18/2015
Citation: Lone, A., Atci, E., Renslow, R., Beyenal, H., Noh, S.M., Fransson, B., Abu-Lail, N., Park, J., Gang, D.R., Call, D. 2015. Colonization of epidermal tissue by Staphylococcus aureus produces localized hypoxia and stimulates secretion of antioxidant and caspase-14 proteins. Infection and Immunity. 83(8):3026-34.

Interpretive Summary: Multidrug resistant Staphylococcus aureus biofilms are a major problem in acute and chronic wounds, but the mechanisms responsible for impaired healing are not well defined. The epidermis is a robust physical and immunological barrier against most pathogens. Keratinocytes, which form the bulk of the epidermis, differentiate into the outer-most protective keratinized barrier of skin and serve as the first line of defense at body surfaces. Oxygen is essential for growth of many bacterial pathogens and large numbers of bacteria growing within a biofilm quickly consume oxygen. Consequently, we hypothesized that colonization of epidermis with S. aureus leads to formation of localized biofilm communities that subsequently deplete oxygen from the underlying epidermis. We found that S. aureus biofilm grows predominantly in sebum-rich areas around hair follicles and associated skin folds. Dissolved oxygen was selectively depleted (2-3 fold) in these locations. Additionally, there is necrosis of all layers of the epidermis by day four post bacterial colonization as determined by histopathology. The colonized epidermal tissue released increased amounts of anti-oxidant proteins and caspase-14. These results indicate the epidermis responds to S. aureus colonization through increased keratinocyte differentiation and shedding.

Technical Abstract: A partial-thickness epidermal explant model was colonized with GFP-expressing S. aureus and the pattern of S. aureus biofilm growth was characterized using electron and confocal laser scanning microscopy. Oxygen concentration in explants and H2O2 in media was quantified using microelectrodes. The relative effective diffusivity and porosity of the epidermis were determined using magnetic resonance imaging. Secreted proteins were identified and quantified using MSE mass spectrometry. We found that S. aureus biofilms grow predominantly in sebum-rich areas around hair follicles and associated skin folds. Dissolved oxygen was selectively depleted (2-3 fold) in these locations, but the relative effective diffusivity and porosity did not change between colonized and control epidermis. Histological analysis revealed keratinocyte damage across all the layers of colonized epidermis after four days of culture. The colonized explants released significantly (P< 0.01) more anti-oxidant proteins of both epidermal and S. aureus origin, consistent with elevated H2O2 concentration found in the media from the colonized explants (P< 0.001). Caspase-14 was also elevated significantly in media from infected explants. While H2O2 induces primary keratinocyte differentiation, caspase-14 is required for terminal keratinocyte differentiation and desquamation. These results are consistent with a localized biological impact from S. aureus in response to simple colonization of the skin surface.