Graduation Date

Summer 8-14-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pathology & Microbiology

First Advisor

Paul D. Fey

Abstract

Skin-dwelling coagulase-negative staphylococci (CoNS), a group of bacteria that includes Staphylococcus epidermidis, has been implicated to promote skin immunity and antimicrobial defense and prohibit colonization of skin by pathogens like S. aureus. As a skin inhabitant, S. epidermidis lives in tight association with corneocytes, the cells that constitute the uppermost layer of the skin epidermis. Yet the molecular mechanism responsible for adhesion of S. epidermidis to corneocytes remains poorly understood. Our study indicated that Accumulation-associated protein (Aap), a cell-wall anchored, fibrillar adhesin mediates bacterial-host interaction, demonstrated by significantly higher corneocyte binding by Aap-positive 1457 mutants as compared to isogenic Aap-negative mutants. Aap is composed of two distinct domains; the A-domain comprises a repeat region and a conserved L-type lectin domain and the fibrillar B-domain is linked to the cell-wall. Our experiments revealed that Aap-mediated binding of S. epidermidis1457 to the skin involved the A-domain, primarily the lectin subdomain. Moreover, isogenic mutants expressing truncated variants of Aap were generated to add rigor and confirm the significance of the individual domains of Aap in adherence to corneocytes. Interestingly, significant corneocyte binding was observed when the lectin subdomain was expressed with the B domain, compared to the mutants expressing the individual domains (A, B, A-lectin or A-repeat). However, expression of the B domain with the full-length A domain resulted in significantly more corneocyte binding than when the B domain was expressed with the lectin subdomain alone. These data suggested that while the A domain lectin subdomain functions to mediate corneocyte binding, the A domain repeat region and the B-domain are also required to provide Aap with enhanced corneocyte binding function. Furthermore, deglycosylation treatments, blocking experiment with sugars and glycan array screening suggested that the glycans expressed in the host stratum-corneum serve as potential binding partners for the Aap-mediated adhesion of S. epidermidis to the corneocytes. In agreement with our results, genome analysis of the predominant commensal strains of CoNS revealed that these staphylococcal species also contain ORFs homologous to the gene aap, thus suggesting that Aap orthologues containing lectin-like domain might provide the basis for staphylococcal colonization of the skin.

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