Quantification of the lateral detachment force for bacterial cells using atomic force microscope and centrifugation

• Published in: Ultramicroscopy 2011, Vol.111 (2), p.131-139
• Main Authors: Zhang, Tong, Chao, Yuanqing, Shih, Kaimin, Li, Xiao-Yan, Fang, Herbert H.P.
• Format: Article
• Language: English
• Subjects: Atomic force microscope; Bacterial Adhesion; Centrifugation; Centrifugation - methods; Escherichia coli; Escherichia coli K12 - physiology; Glass; Hardness; Lateral detachment force; Mechanics; Microscopy, Atomic Force - methods; Reproducibility of Results
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2010.10.005

To determine the lateral detachment force for individual bacterial cells, a quantitative method using the contact mode of an atomic force microscope (AFM) was developed in this study. Three key factors for the proposed method, i.e. scan size, scan rate and cantilever choice, were evaluated and optimized. The scan size of 40×40 μm 2 was optimal for capturing sufficient number of adhered cells in a microscopic field and provide adequate information for cell identification and detachment force measurement. The scan rate affected the measurement results significantly, and was optimized at 40 μm/s considering both force measurement accuracy and experimental efficiency. The hardness of applied cantilevers also influenced force determination. The proposed protocol for cantilever selection is to use those with the lowest spring constant first and then step up to a harder cantilever until all cells are detached. The lateral detachment force of Escherichia coli cells on polished stainless steel and a glass-slide coated with poly- l-lysine were measured as 0.763±0.167 and 0.639±0.136 nN, respectively. The results showed that the established method had good repeatability and sensitivity to various bacteria/substrata combinations. The detachment force quantified by AFM (0.639±0.136 nN) was comparable to that measured by the centrifugation method (1.12 nN). ► A quantitative method via AFM is developed to measure the lateral detachment force of an attached cell. ► The parameters of AFM operation for this method are optimized. ► The tests using E. coli on different substrata show that the method has good repeatability and sensitivity. ► The method could obtain reliable results that are comparable to those using the centrifugation approach.