Title: Quantification of bacterial adhesion forces using atomic force microscopy (AFM)

Journal: Journal of Microbiological Methods

Authors: Herbert H. P. Fanga, Kwong-Yu Chanb and Li-Chong Xua

Institute:
a Centre for Environmental Engineering Research, Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
b Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong

The original and creativity of paper: 
 High resolution of topographical image was illustrated using atomic force microscopy. Moreover, the tip-cell interaction forces as well as surface elasticity were quantified.

Summary:
In this study, the tip-cell interaction forces of a bacterial cell surface and elasticity were quantified to provide the deeper understanding of biofilm formation. The results revealed that atomic force microscopy has ability to measure the adhesion forces on a single bacterium cell surface, on cell?cell interface, and on the periphery of the cell?substratum contact surface. Moreover, it provides high resolution topographic images couple with quantitative information about surface force and elasticity.
In order to measure interaction force, sample will be extended upward approaching the tip from A to B, and then because of attractive force the tip is pulled down and jump-to-contact with the surface at B. Since the sample continues to extend, the cantilever bends up. After that, tip will be retracted from the sample when the tip reaches position C. Finally, because of the adhesion force, the cantilever begins to bend downward (CD) until reaching the break point (D) at which the cantilever rebounds sharply upward to E. Fig. 1 shows a typical force?distance curve between the tip and the cell surface.
 
Fig. 1 typical force?distance curve between the AFM tip and bacterium surface.

In addition, this force?distance curve can be provided the information about elasticity of the sample surface. The elasticity of the sample surface can be observed from the slope of the BC section (see Fig. 1).

Contribution: 
The methodology mentioned in this paper can be applied to determined interaction force and elasticity of fouled membrane sample which will be provided better understanding of the fouling mechanism.

By Monruedee Moonkhum
Email: moon@gist.ac.kr