Interfacial nanomechanical heterogeneity of the E. coli biofilm matrix.

The interface between bacterial biofilms and their environment plays a vital role in the recalcitrance of biofilms to biological, chemical, and mechanical threats. Nonetheless, we know little about the physical parameters that dictate the interfacial morphology and nanomechanics of biofilms. Here, we present a robust, reproducible, and quantitative platform based on atomic force microscopy (AFM) that allows for correlated high-resolution imaging of the morphology and nanomechanical properties of an intact E. coli biofilm-under physiological conditions. We developed analysis algorithms based on linearized Hertzian contact mechanics to discriminate, at the nanoscale, the elasticity of the extracellular polymeric substances (EPS) from bacteria within the biofilm. We were able to identify two distinct EPS populations with approximately 10-fold difference in their elastic properties. A correlation between EPS' elasticity and morphology points to different functions of the EPS populations within a mature E. coli biofilm. Thus, beyond high-resolution nanomechanical maps of a complex biological sample, we provide direct evidence of nanoscale heterogeneities at the biofilm interface. As interactions between biofilms and various antimicrobial agents occur at the nanoscale, understanding the physico-mechanical properties at the interface-with nanometer resolution-is imperative in devising targeted strategies against bacterial biofilms. We anticipate that in conjunction with other existing approaches, our quantitative imaging platform will provide mechanistic insights into the action and effectiveness of antimicrobials and antibiofilm agents.