Impact of sodium nitroprusside concentration added to batch cultures of Escherichia coli biofilms on the c-di-GMP levels, morphologies and adhesion of biofilm-dispersed cells

Biofilm dispersion can be triggered by the application of dispersing agents such as nitric oxide (NO)-donors, resulting in the release of biofilm-dispersed cells into the environment. In this work, biofilm-dispersed cells were obtained by adding different concentrations of NO-donor sodium nitroprusside (0.5, 5, 50 mu M, and 2.5 mM of SNP) to batch cultures of pre-formed Escherichia coli biofilms. Except for those dispersed by 5 mu M of SNP, biofilm-dispersed cells were found to be wider and longer than the planktonic cells and to have higher c-di-GMP levels and greater adhesion forces to silicon nitride surfaces in water as measured by atomic force microscope. Consequently, the optimum concentration of SNP to disperse E. coli biofilms was found to be 5 mu M of SNP, whose addition to batch cultures resulted in a significant biofilm dispersion and the dispersed cells having c-di-GMP levels, morphologies and adhesion strengths similar to their planktonic counterparts.