(197f) Establishing Relationships between Local pH and Mechanics in Staphylococcus Epidermidis Biofilms

Bacterial biofilms are complex, structured communities of microbial cells encased within self-produced extracellular polymeric matrix materials. Staphylococcus epidermidis biofilms frequently cause infections on catheters and implanted medical devices, and are responsible for nearly 120,000 infections annually¹. As S. epidermidis biofilms grow, acidic waste products such as lactic acid, acetic acid, and formic acid can accumulate within their structures. Additionally, S. epidermidis biofilm matrix materials have been shown to be unstable and more rigid at lower pH values and stable and softer at higher pH values². We hypothesized that local pH gradients and heterogenous local mechanics exist within S. epidermidis biofilms due to the structural heterogeneity and nonuniform distribution of acidic waste products in biofilms. To test this hypothesis, we used confocal laser scanning microscopy (CLSM) and image analysis techniques to quantitatively map local pH gradients and determine local biofilm mechanical properties. The most acidic microenvironments were found to be at the biofilm-substrate interface during biofilm growth in both static culture and at physiological shear stresses. Local mechanical properties were more heterogeneous in biofilms grown at physiological shear stresses than in static culture. S. epidermidis biofilm mechanics varied locally with pH in both static growth environments and at physiological shear stresses, where local pH > 6.9 within biofilms resulted in softer mechanics than in biofilm regions with lower average pH. This work advances how variations in the local microenvironment can shift biofilm mechanics and has implications for the development of biofilm disruption techniques targeting local biofilm mechanical properties.

¹Kourtis, A. P. et. al. (2019). Morbidity and mortality weekly report, 68(9), 214–219.

²Stewart, E. J., Ganesan, M., Younger, J. G., & Solomon, M. J. (2015). Scientific reports, 5, 13081.