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Functional blocking of Staphylococcus aureus adhesins following growth in ex vivo media
Ruth C Massey1, Shobana R Dissanayeke, Brian Cameron
1Nuffield Department of Clinical Laboratory Sciences, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.
Abstract:
Defining the role of Staphylococcus aureus adhesins in disease pathogenesis may depend on the use of bacteria grown in culture media that more closely reflect the human milieu than conventional broth. This study examined the functional effect on S. aureus adhesins following growth in an ex vivo medium containing a complex mixture of human proteins (used peritoneal dialysate) relative to growth in Todd-Hewitt broth. The adherence of S. aureus, cultured in dialysate, to fibronectin and fibrinogen was markedly reduced despite the expresion of full-length ClfA, ClfB, and fibronectin-binding proteins. Growth in dialysate resulted in the acquisition of a surface coat, as visualized by transmission electron microscopy, which was shown to contain fibronectin, fibrinogen, and immunoglobulins. Adherence of S. aureus to fibrinogen following growth in dialysate was significantly reduced by expression of protein A but was restored following growth in immunoglobulin-depleted dialysate. We conclude that bacterial adherence to solid-phase protein is critically dependent on the culture medium, that S. aureus adhesins may become saturated with target protein prior to contact with solid surfaces, and that there is an interaction between fibrinogen-binding proteins and immunoglobulin bound to protein A following contact with host proteins. These findings have important implications for future studies of S. aureus adhesins.
Insights
Bacterial adhesin function in Staphylococcus aureus is altered by human protein exposure. Growth in dialysate reduced adherence, suggesting proteins saturate adhesins before surface contact.
Area of Science:
- Microbiology
- Pathogenesis
- Bacterial Adherence
Background:
- Staphylococcus aureus adhesins are crucial for disease development.
- Conventional bacterial culture media may not accurately mimic the human environment.
- Understanding adhesin function requires culture conditions closer to in vivo settings.
Purpose of the Study:
- To investigate the impact of ex vivo human protein exposure on S. aureus adhesin function.
- To compare bacterial adherence after growth in used peritoneal dialysate versus Todd-Hewitt broth.
- To elucidate the mechanisms behind altered adhesin activity in a human-like milieu.
Main Methods:
- Culturing S. aureus in used peritoneal dialysate and Todd-Hewitt broth.
- Assessing bacterial adherence to fibronectin and fibrinogen.
- Utilizing transmission electron microscopy to visualize bacterial surface changes.
- Analyzing the effect of protein A expression and immunoglobulin depletion on adherence.
Main Results:
- S. aureus grown in dialysate showed reduced adherence to fibronectin and fibrinogen, despite expressing adhesins.
- A surface coat containing fibronectin, fibrinogen, and immunoglobulins formed on bacteria grown in dialysate.
- Protein A expression reduced adherence to fibrinogen, which was reversed by immunoglobulin depletion.
- Adherence was significantly impacted by the culture medium composition.
Conclusions:
- Bacterial adherence to proteins is highly dependent on the culture medium.
- S. aureus adhesins may become saturated with host proteins in the culture medium, limiting surface adherence.
- Interactions between bacterial adhesins (like fibrinogen-binding proteins) and host proteins (immunoglobulins bound to Protein A) influence adherence.