Investigation of Adhesion Forces on the Surface of Borrelia burgdorferi Using AFM*

The Lyme disease spirochete, Borrelia burgdorferi (Bb), is the leading cause of arthropod-borne disease in the USA. Adhesion is important to the establishment of infection and contributes to dissemination, persistence, and immune evasion. Therefore, understanding bacterial adhesion at the molecular level is crucial. Atomic Force Microscopy (AFM) can provide both the topography and mechanical properties of biological samples. With AFM, we measured adhesive forces between non-functionalized AFM tips and adhesins on the surface of live Bb. Using contact-mode force spectroscopy we extracted the tip-bacteria adhesion characteristics of three different B. burgdorferi cell lines (Wild,  AD3BLKO, HPJ) with progressively higher mutations. From over 6000 total measurements, probability density functions for each mutant line were extracted. Results of the experiment show significant adhesion forces between non-functionalized AFM cantilevers and B. burgdorferi, exhibiting a linear decrease in maximum adhesion with an increase in genes removed. Similarly, binding probability from successful vs unsuccessful adhesion events exhibits a linear decrease as a function of increased mutation. Current work is being done to characterize the adhesion force between fibronectin functionalized cantilevers and proteins isolated from B. burgdorferi.