Screening the mechanical stability of Escherichia coli biofilms through exposure to external, hydrodynamic shear forces

The desire to attain a deeper understanding of the fundamental aspects governing the mechanical properties of biofilms has become more prominent in recent years. This has largely been due to the realization that these sessile microbial communities often withstand environments where hydrodynamic turbulence and shearing forces are considerable. In the present study, Escherichia coli K-12 was used as a model system to develop a laboratory technique that can be used to quickly screen the mechanical integrity or stability of laboratory cultivated bacterial biofilms when exposed to such external, hydrodynamic shear forces. The screening method utilizes a custom-built, automated water jetting apparatus to generate and precisely apply a pressurized stream of water directly to biofilms cultured in multi-well plates. An optimized set of water jetting parameters was determined to resolve subtle to moderate differences in the mechanical stability of isogenic strains of E. coli K-12 as a function of percent biofilm removal. Mutations in both flagella biosynthesis (fliA) and acetate metabolism (ackA and ackA pta) were shown to impair the mechanical integrity of 24-h biofilms, while a "housekeeping" strain deficient in arginine metabolism (argD) exhibited a mechanical stability profile comparable to the parent strain.