Editorial: In Focus Issue on Bacterial-Surface Interactions

The In Focus issue of Biointerphases on Bacterial-Surface Interactions highlights the quantitative techniques and analysis systems being developed to understand the interactions that occur when bacteria come in contact with biological and synthetic interfaces. Bacterial–surface interactions affect a diverse range of health and medical, energy, and infrastructure systems including wound repair, the gut microbiome, microbial fuel cells, and marine biofouling. We received submissions detailing research addressing challenges from across the field that were seeking to address both fundamental and applied questions.

The immobilization and incorporation of active ingredients at surfaces is well established, and while antibiotics have been incorporated in polymers as antibacterials for some time, treatment strategies for fungal pathogens are not as common. Michl et al. have demonstrated that surface immobilized antifungal agents can reduce fungal biofilms by >4 log units to below the threshold of the tests. Critically, the presence of these agents was shown to not affect mammalian cells, suggesting that these films could be suitable for antifungal medical device coatings.¹ The creation of antimicrobial systems from different metallic micro- and nanomaterials were explored in two studies that investigated both the efficacy and the mechanisms of anti-microbial action. Interestingly, the emphasis on high volume applications in each case presented specific challenges, with Tanasic et al.² focusing on the properties of additives for surface paints and coatings in hospitals while Heiss et al.³ focused on the stability and long term activity of AgRu coatings on microparticles for water purification systems.

The increased introduction of metal containing nanomaterials into industrial processes means that their influence can reach into a far wider range of ecosystems, including our soil microbiome. Lewis and Unrine⁴ have developed a respiration-based assay for evaluating the toxicity of engineering nanomaterials (ENMs) and metals to isolated bacterial species/strains found in soils and other plant biomass. Their work demonstrated that the surface and structure of the nanomaterials influenced behavior, and that biological species specific information is also required. This approach can give quantitative insight into the mechanisms of metabolic responses of bacteria to ENMs, metal ions, and antibiotics.

Antimicrobial peptides continue to be a central theme in our community, and the need to provide quantitative insights into the mechanisms of their different actions has been highlighted in two studies on both native⁵ and synthetic environments.⁶ Both studies demonstrated the central role of biophysical techniques to both engineer and characterize biomaterials interfaces with quartz crystal microbalance, circular dichroism, XPS, and electrical impedance spectroscopy used to quantify the surface interactions and properties of the systems. The work of Raman et al.⁶ shows how antimicrobial peptides can be engineered into device coatings as capture agents for intact bacterial cells and the endotoxins associated with sepsis. Shahmiri et al.⁵ in turn created new insight into the design of surface-acting antimicrobial peptides, demonstrating that aromatic residues provide a membrane anchor for peptides which can provide a downstream effect.

Finally, important insights gained from fundamental quantitative studies in bacterial–surface interactions were highlighted in two very different technique-focused articles exploring the adhesion properties of bacteria on metallic surfaces⁷ and the surface interactions associated with direct interspecies electron transfer that occurs in biofilms.⁸ Davoudi et al.⁷ explored the role of surface nanostructure and adhesion processes in sea-water bacteria, with key insights showing the change in adhesion that occurred when pH and ionic strength were varied, two key parameters in studying water associated biofilms. Wei et al.⁸ used ToF-SIMS to explore the syntrophic Geobacter aggregates and electron transfer events that occur in these complex biofilms. Their studies demonstrated that ToF-SIMS could help identify the different bacterial populations, and excitingly, could be used to monitor quorum sensing molecules within the biofilms and aggregates, enabling the interplay of signaling and community formation to be examined.

This In Focus issue adds breadth and further depth to the longstanding emphasis Biointerphases has placed on all aspects of bacterial-surface interactions. In addition to the issue, the Editors have created a collection of our top articles in antimicrobial surfaces which can provide more insight into this field.