Adaptation of Staphylococcus aureus to the Human Skin Environment Identified Using an ex vivo Tissue Model

Abstract

The healthy human epidermis provides physical protection and is impenetrable for pathogenic microbes. Nevertheless, commensal and pathogen bacteria such as Staphylococcus aureus are able to colonize the skin surface, which may subsequently lead to infection. To identify and characterize regulatory elements facilitating adaptation of S. aureus to the human skin environment we used ex vivo tissue explants and quantified S. aureus gene transcription during co-culture. This analysis provided evidence for a significant downregulation of the global virulence regulator agr upon initial contact with skin, regardless of the growth phase of S. aureus prior to co-culture. In contrast, the alternative sigma factor B (sigB) and the antimicrobial peptide-sensing system (graRS) were expressed during early colonization. Consistently, sigB target genes such as the clumping factor A (clfA) and fibrinogen and fibronectin binding protein A (fnbA) were strongly upregulated upon skin contact. At later timepoints of the adhesion process, wall teichoic acid (WTA) synthesis was induced. Besides the expression of adhesive molecules, transcription of molecules involved in immune evasion were increased during late colonization (staphylococcal complement inhibitor and staphylokinase). Similar to nasal colonization, enzymes involved in cell wall metabolism (sceD and atlA) were highly transcribed. Finally, we detected a strong expression of proteases from all three catalytic classes during the entire colonization process. Taken together, we here present an ex vivo skin colonization model that allows the detailed characterization of the bacterial adaptation to the skin environment.

The Staphylococcus epidermidis Transcriptional Profile During Carriage

“…Given the low abundance of fibrinogen on human skin, the high expression in toe web spaces could indicate additional, so far uncharacterized functions of s dr G. The high expression of WTA was also demonstrated during nasal colonization of S. aureus ( Burian et al, 2010a , b ). Again, similar to persistent colonization of the human nose ( Burian et al, 2010b ) and early colonization of the skin ( Burian et al, 2021 ) by S. aureus , we observed a strong expression of the autolysin sce D. Interestingly, although sce D was expressed in both niches, it was clearly overrepresented in the nose. This high sce D transcription in both species underscore the importance of the lytic transglycosylase and may therefore be a useful candidate for developing a targeted therapy by inhibition of sce D. Such therapy could play a role especially in atopic dermatitis when massive colonization with S. aureus is responsible for the severity of the disease ( Totte et al, 2016 ) and S. epidermidis also has a deleterious effect by expressing, for example, the protease ecp A ( Cau et al, 2021 ).…”

“…Besides PGA, resistance to AMPs is mediated by the expression of dlt A, which leads to the d-alanylation of teichoic acids, thereby reducing the anionic charge of the bacterial surface ( Simanski et al, 2013 ). Since the putative chitinase B (SE0760) is selectively expressed on skin and it is known to mediate skin invasion ( Zhang et al, 2003 ), it would be interesting to investigate in further studies whether a SE0760 mutant is less able to colonize and persist on skin using, for example, our newly established human colonization model ( Burian et al, 2021 ).…”

“…Relative quantification of S. epidermidis transcripts by qPCR was performed as described previously ( Burian et al, 2021 ). Briefly, qPCR was carried out using the 7300 Real-Time PCR instrument (Applied Biosystems) in combination with the KAPA SYBR® FAST qPCR Master Mix (2×) ABI Prism (Merck).…”

Rapid Aggregation of Staphylococcus aureus in Synovial Fluid Is Influenced by Synovial Fluid Concentration, Viscosity, and Fluid Dynamics, with Evidence of Polymer Bridging

“…It has been reported that, within 30 min of gentamicin exposure (100× the MIC), there is a significant elevation in the expression of SigB, a stress-responsive alternative sigma factor ( 26 , 27 ). SigB activity positively influences the expression of clumping factors and fibronectin-binding proteins, which could explain the increase in aggregation observed with the gentamicin-treated bacteria ( 28 – 30 ). Taken together, these findings confirm our speculation that bridging aggregation does occur through the rapid interaction of bacterial adhesins with fibrinogen, but they suggest that it is not the only contributor to the aggregate phenotype.…”

Rapid aggregation of Staphylococcus aureus in synovial fluid is influenced by synovial fluid concentration, viscosity, and fluid dynamics-with evidence of polymer bridging

“…It has been reported that within 30 minutes of gentamicin exposure (100x the MIC), there is a significant elevation in the expression of SigB- a stress-responsive alternative sigma factor (26),(27). SigB activity positively influences the expression of clumping factors and fibronectin-binding proteins, which could explain the increase in aggregation observed with the gentamicin-treated bacteria (28),(29),(30). Taken together, these findings confirm our speculation that bridging aggregation does occur through the rapid interaction of bacterial adhesins with fibrinogen but suggest that it alone is not the only contributor to the aggregate phenotype.…”