The ability of bacteria to adhere to solid surfaces, proliferate and make a biofilm is the primary cause of food contamination, hospital infections and failures of long-term biomedical implants. Consequently, there is an increasing interest in developing surfaces with antibacterial properties in many areas such as food processing and health-related fields like medicine and dentistry.
In order to design antibacterial surfaces it is necessary to understand the physical and molecular interactions governing the bacterial adhesion to a surface, which is the first crucial step of biofilm formation. Several methods have been developed to evaluate these mechanisms and to identify the main influencing parameters. Static adhesion assays can provide experimental samples suitable for the qualitative or semi-quantitative measurements of bacterial adhesion. Fluid shear systems have been used to simulate the in vivo dynamic mechanical stress and to obtain global probabilistic measurements of the bacterial adhesion strength [1].
Nevertheless, the physical interactions involved in bacterial adhesion have not been understood in detail and the development of experimental procedures for further investigations is essential.
For a more focused investigation on the adhesion mechanisms, techniques comprising the manipulation of single bacteria are more appropriate.
Atomic Force Microscopy (AFM) can be used to obtain local information about the first physicochemical interaction phase of bacterial attachment to a surface, by the measurement of force-distance curves. The process can be studied by two different experimental approaches: i) by measuring the interaction forces between bacterial cells and a standard AFM tip [1] or ii) by measuring the interaction forces between bacteria on AFM tip and different surfaces [2].
In this work we develop an experimental procedure to obtain quantitative measurements of bacterial adhesion to different surfaces, by recording force-distance curves using probes coated with different bacterial species. Force-distance curves measurements are carried out, in air and in liquid, on substrates with different properties (chemical composition, hydrophobicity, charge)
The influence of the experimental conditions on the results is analyzed with the aim of assessing the most appropriate procedure.
Also, the results are discussed focusing on the influence of different physicochemical properties of bacteria and surfaces in the adhesion mechanism.
Overall, this work represents a preliminary study on the capability of AFM force distance curves measurements to investigate the physicochemical mechanism involved in the bacterial adhesion to abiotic surfaces.
[1] M. Katsikogianni et al., Eur Cell Mater 8 (2004) 37-57
[2] Y.J. Oh et al., Ultramicroscopy 109 (2009) 874–880