(142d) Impact of NaCl Stress On the Mechanical and Material Properties of Staphylococcus Epidermidis Biofilms

Biofilms are aggregates of bacteria encapsulated with a protective layer of extracellular polysaccharide (EPS). Staphylococcus epidermidis biofilms are frequent in hospital-related infections associated with contaminated medical devices.  Studies have shown that NaCl can contribute to the overexpression of the ica operon, which plays a role in the production of EPS (Conlon, K.M., J. Bacteriology, 2002).   This study determined the effect of osmotic stress imparted by high concentrations of NaCl on material and mechanical properties of S. epidermidis RP62A bacterial biofilms. 

We probed the intercellular microstructure by analysis of 3D image volumes acquired by confocal laser scanning microscopy.  We observed that increasing NaCl concentration significantly decreased the cellular density of biofilms grown in a 0.011 Pa shear environment.  Parallel plate rheology was used to determine the mechanical properties of S. epidermidis biofilms under conditions of both linear and non-linear deformations.  A non-monotonic effect of NaCl on the magnitude of the elastic and vicsous moduli of the biofilms was observed.  Size-exclusion chromatography coupled with multi-angle laser light scattering and refractive index detection was used to measure the molar mass distribution of the EPS from biofilms grown under different NaCl concentrations.  The relationship among the EPS molar mass, the intercellular structure, and the biofilm rheology is discussed so as to determine the structural and polymeric origins of the observed salt stress effects on biofilm mechanical properties.