Single-Cell Force Spectroscopy of Bacteria Enabled by Naturally Derived Proteins

Bringing the study of bacterial adhesion down to a single-cell level is critical for understanding the molecular mechanisms involved in initial bacterial attachment. We have developed a simple and versatile method for making single-cell bacterial probes to study the adhesion of single bacterial cells by atomic force microscopy (AFM). A single-cell probe was made by picking up a bacterial cell from a glass surface using a tipless AFM cantilever coated with a commercial cell adhesive Cell-Tak. The method was applied to four different bacterial strains, and single-cell adhesion was measured on three surfaces (fresh glass, hydrophilic glass, and mica). Attachment to the cantilever was stable during the AFM force measurements that were conducted for 2 h, and viability was confirmed by Live/Dead fluorescence staining at the end of each experiment. The adhesion force and final rupture length were dependent on bacterial strains, surfaces properties, and contact time. The single-cell probe offers control of cell immobilization and thus holds advantages over the commonly used multicell probes with which random immobilization is obtained by submerging the cantilever in a bacterial suspension. The reported method provides a general platform for investigating single-cell interactions of bacteria with different surfaces and other cells by AFM force spectroscopy, thus improving our understanding of the mechanisms of bacterial attachment.