Measuring Cell Surface Elasticity on Enteroaggregative Escherichia coli 042 Wild Type and Dispersin Mutant by Atomic Force Microscopy

Enteroaggregative Escherichi coli (EAEC) 042 is a pathogenic strain of E.coli that produces a severe diarrhea in humans. A mutant of EAEC 042 that does not produce dispersin, a cell surface protein, is not pathogenic. It has been proposed that dispersin imparts a positive charge to the bacterial cell surface allowing the bacteria to colonize on the negatively charged intestinal mucosa. However, physical properties of the bacterial cell surface, such as rigidity, may be influenced by the presence of dispersin and may contribute to pathogenicity. Using the system developed in our laboratory for mounting and imaging bacterial cells by atomic force microscopy (AFM), in liquid, on gelatin coated mica surfaces, studies were initiated to measure cell surface elasticity of both wild type EAEC 042 that produces dispersin, and the mutant that does not produce dispersin. This was accomplished using AFM force distance (FD) spectroscopy on the wild type and mutant grown in liquid or on solid medium. Images in liquid and in air of both the wild type and mutant grown in liquid and on solid media are presented. This work was done to establish a baseline for future AFM force interaction studies to determine the pathogenic role of the dispersin protein in the wild type bacteria.