A combination of force spectroscopic experiments and theoretical simulations reveals the molecular processes responsible for the adhesion of S. aureus.

No abstract

Bacterial adhesion to nanostructured surfaces can be quantified by surface morphometry: the surface area that is accessible in a certain depth for tethering cell wall molecules equals the fraction of adhesion force as compared to a smooth surface.

Bacterial adhesion is a crucial step during the development of infections as well as the formation of biofilms. Hence, fundamental research of bacterial adhesion mechanisms is of utmost importance. So far, less is known about the size of the contact area between bacterial cells and a surface. This gap will be filled by this study using a single-cell force spectroscopy-based method to investigate the contact area between a single bacterial cell of Staphylococcus aureus and a solid substrate. The technique relies on the strong influence of the hydrophobic interaction on bacterial adhesion: by incrementally crossing a very sharp hydrophobic/hydrophilic interface while performing force-distance curves with a single bacterial probe, the bacterial contact area can be determined. Assuming circular contact areas, their radii - determined in our experiments - are in the range from tens of nanometers to a few hundred nanometers. The contact area can be slightly enlarged by a larger load force, yet does not resemble a Hertzian contact, rather, the enlargement is a property of the individual bacterial cell. Additionally, Staphylococcus carnosus has been probed, which is less adherent than S. aureus, yet both bacteria exhibit a similar contact area size. This corroborates the notion that the adhesive strength of bacteria is not a matter of contact area, but rather a matter of which and how many molecules of the bacterial species' cell wall form the contact. Moreover, our method of determining the contact area can be applied to other microorganisms and the results might also be useful for studies using nanoparticles covered with soft, macromolecular coatings.

Hydroxyapatite substrates are common biomaterials, yet samples of natural teeth do not meet the demands for well-defined, highly reproducible properties. Pellets of hydroxyapatite were produced via the field assisted sintering technology (FAST) as well as via pressureless sintering (PLS). The applied synthesis routes provide samples of very high density (95%-99% of the crystallographic density) and of very low surface roughness (lower than 1 nm when averaged per 1 μm). The chemical composition of the raw material (commercial HAP powder) as well as the crystalline structure is maintained by the sintering processes. These specimens can therefore be considered as promising model surfaces for studies on the interactions of biomaterial with surfaces of biological relevance, as demonstrated for the adsorption of BSA proteins.

Surface patterning in the micro- and nanometer-range by means of pulsed laser interference has repeatedly proven to be a versatile tool for surface functionalization. With these techniques, however, the surface is often changed not only in terms of morphology but also in terms of surface chemistry. In this study, we present an in-depth investigation of the chemical surface modification occurring during surface patterning of copper by ultrashort pulsed direct laser interference patterning (USP-DLIP). A multimethod approach of parallel analysis using visualizing, topography-sensitive, and spectroscopic techniques allowed a detailed quantification of surface morphology as well as composition and distribution of surface chemistry related to both processing and atmospheric aging. The investigations revealed a heterogeneous surface composition separated in peak and valley regions predominantly consisting of Cu2O, as well as superficial agglomerations of CuO and carbon species. The evaluation was supported by a modeling approach for the quantification of XPS results in relation to heterogeneous surface composition, which was observed by means of a combination of different spectroscopic techniques. The overall results provide a detailed understanding of the chemical and topographical surface modification during USP-DLIP, which allows a more targeted use of this technology for surface functionalization.

The atomic force microscope (AFM) evolved as a standard device in modern microbiological research. However, its capability as a sophisticated force sensor is not used to its full capacity. The AFM turns into a unique tool for quantitative adhesion research in bacteriology by using "bacterial probes". Thereby, bacterial probes are AFM cantilevers that provide a single bacterium or a cluster of bacteria as the contact-forming object. We present a step-by-step protocol for preparing bacterial probes, performing force spectroscopy experiments and processing force spectroscopy data. Additionally, we provide a general insight into the field of bacterial cell force spectroscopy.

Data presented in this article describe bacterial and fungal repellent properties of 2D-films and 3D-hydrogels made of different recombinantly produced spider silk proteins based on consensus sequences of Araneus diadematus dragline silk proteins (fibroin 3 and 4). Here, the attachment, growth, and microbial colonization of Streptococcus mutans (S. mutans) as well as Candida albicans (C. albicans) on plane and micro-patterned films were visualized by scanning electron microscopy (SEM). Also, microbial viability data are provided of Escherichia coli (E. coli) and Pichia pastoris (P. pastoris) on hydrogels made of eADF4(C16) and eADF4(C16)-RGD, quantified using the Alamar blue assay. Experimental results, design of a post-operative contamination model of microbes with mammalian cells, and methods in the data article refer to the research paper “Engineered spider silk-based 2D and 3D materials prevent microbial infestation” published recently [1] .