Force measurements of bacterial adhesion on metals using a cell probe atomic force microscope

The adhesion of microbial cells to metal surfaces in aqueous media is an important phenomenon in both the natural environment and engineering systems. The adhesion of two anaerobic sulfate-reducing bacteria ( Desulfovibrio desulfuricans and a local marine isolate) and an aerobe ( Pseudomonas sp.) to four polished metal surfaces (i.e., stainless steel 316, mild steel, aluminum, and copper) was examined using a force spectroscopy technique with an atomic force microscope (AFM). Using a modified bacterial tip, the attraction and repulsion forces (in the nano-Newton range) between the bacterial cell and the metal surface in aqueous media were quantified. Results show that the bacterial adhesion force to aluminum is the highest among the metals investigated, whereas the one to copper is the lowest. The bacterial adhesion forces to metals are influenced by both the electrostatic force and metal surface hydrophobicity. It is also found that the physiological properties of the bacterium, namely the bacterial surface charges and hydrophobicity, also have influence on the bacteria–metal interaction. The adhesion to the metals by Pseudomonas sp. and D. desulfuricans was greater than by the marine SRB isolate. The cell–cell interactions show that there are strong electrostatic repulsion forces between bacterial cells. Cell probe atomic force microscopy has provided some useful insight into the interactions of bacterial cells with the metal surfaces. The adhesion forces for initial biofilm formation to the metal surfaces can be quantified by using AFM force measurement with a cell probe.