Ferumoxytol Treatment of Biofilms

The biofilms were topically treated twice daily by placing them in 2.8 ml of ferumoxytol (1 mg ml⁻¹) in 0.1 M NaOAc (pH 4.5) or vehicle-control (buffer only) for 10 min as described in Supplementary Fig. 4a. At the end of the experimental period (43 h), the ferumoxytol and vehicle treated biofilms were placed in 2.8 ml of 1% H₂O₂ or buffer for 5 min. After H₂O₂ exposure, the biofilms were removed and homogenized by sonication as described above; the sonication procedure provides optimum dispersal and maximum recoverable counts in our biofilm model without killing bacterial cells^{19 (link)}. The homogenized suspension was subjected to microbiological and biochemical methods^{19 (link),27 (link)}. The total number of viable cells in each of the treated biofilms was determined by colony forming units (CFU), while insoluble extracellular polysaccharides was extracted and quantified using colorimetric assays^{19 (link),27 (link)}.