Understanding How Staphylococcal Autolysin Domains Interact With Polystyrene Surfaces.

Radha P Somarathne,Joo Youn Park,Rahul Yadav,Emily R Chappell,Y Randika Perera,Nicholas C Fitzkee

doi:10.3389/fmicb.2021.658373

Radha P Somarathne, Joo Youn Park + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2021.658373

Copy DOI

Abstract

Biofilms, when formed on medical devices, can cause malfunctions and reduce the efficiency of these devices, thus complicating treatments and serving as a source of infection. The autolysin protein of Staphylococcus epidermidis contributes to its biofilm forming ability, especially on polystyrene surfaces. R2ab and amidase are autolysin protein domains thought to have high affinity to polystyrene surfaces, and they are involved in initial bacterial attachment in S. epidermidis biofilm formation. However, the structural details of R2ab and amidase binding to surfaces are poorly understood. In this study, we have investigated how R2ab and amidase influence biofilm formation on polystyrene surfaces. We have also studied how these proteins interact with polystyrene nanoparticles (PSNPs) using biophysical techniques. Pretreating polystyrene plates with R2ab and amidase domains inhibits biofilm growth relative to a control protein, indicating that these domains bind tightly to polystyrene surfaces and can block bacterial attachment. Correspondingly, we find that both domains interact strongly with anionic, carboxylate-functionalized as well as neutral, non-functionalized PSNPs, suggesting a similar binding interaction for nanoparticles and macroscopic surfaces. Both anionic and neutral PSNPs induce changes to the secondary structure of both R2ab and amidase as monitored by circular dichroism (CD) spectroscopy. These changes are very similar, though not identical, for both types of PSNPs, suggesting that carboxylate functionalization is only a small perturbation for R2ab and amidase binding. This structural change is also seen in limited proteolysis experiments, which exhibit substantial differences for both proteins when in the presence of carboxylate PSNPs. Overall, our results demonstrate that the R2ab and amidase domains strongly favor adsorption to polystyrene surfaces, and that surface adsorption destabilizes the secondary structure of these domains. Bacterial attachment to polystyrene surfaces during the initial phases of biofilm formation, therefore, may be mediated by aromatic residues, since these residues are known to drive adsorption to PSNPs. Together, these experiments can be used to develop new strategies for biofilm eradication, ensuring the proper long-lived functioning of medical devices.

Highlights

Staphylococcus epidermidis is a very common pathogen known to cause a variety of infections, including those involving medical implants and devices (McCann et al, 2008; Büttner et al, 2015; Zheng et al, 2018)
Our bacterial growth experiments show no consistent effect on cell division for concentrations of protein in solution up to 10 μM. These results strongly suggest a mechanism whereby biofilm formation is blocked by adsorption of R2ab and amidase to the polystyrene surface, and not a mechanism where cell density is reduced by the presence of these domains in solution
circular dichroism (CD) is sensitive to scattering in the far-UV range, and we found that the neutral polystyrene nanoparticles (PSNPs) would aggregate and give poor signal at high protein concentrations

Summary

Introduction

Staphylococcus epidermidis is a very common pathogen known to cause a variety of infections, including those involving medical implants and devices (McCann et al, 2008; Büttner et al, 2015; Zheng et al, 2018). The cell wall of S. epidermidis contains protein, nucleic acid, and peptidoglycan components (Büttner et al, 2015), and a major protein component of the cell wall is the peptidoglycan hydrolase, autolysin (AtlE). The protein is non-covalently associated with the cell wall through interactions between the R1 and R2 repeats and lipoteichoic acid (LTA) (Zoll et al, 2012). AtlE is known to take part in its primary attachment to surfaces, especially to polystyrene surfaces (Houston et al, 2011). Both amidase and R2ab are required for S. epidermidis to be biofilm positive on polystyrene surfaces (Heilmann et al, 1997; Zoll et al, 2012)

Objectives

Methods

Findings

Discussion

Conclusion