Western blot analyses for LasB were performed using standard protocols as previously described [37 (link)]. Briefly, equal concentration of protein samples (from bacterial culture supernatants) were resolved by SDS-PAGE and electro-blotted onto Immobilon P polyvinylidene difluoride membranes (Millipore, Burlington, MA, USA). The membranes were then incubated for 60 min at room temperature in blocking solution (3% bovine serum albumin in PBS), followed by a 4-h incubation with polyclonal antibody against P. aeruginosa LasB (a gift from Professor Dennis Ohman, Virginia Commonwealth University). The membranes were hybridized with horseradish peroxidase-conjugated goat anti-rabbit IgG secondary antibody. The immune complexes were visualized using the Amersham ECL Western Blotting Detection System (Danaher Corporation, Washington, D.C., USA) on HyBlot CL autoradiography films (Denville Scientific, InC, Metuchen, NJ, USA). In order to assure reproducibility, western blotting was performed twice with similar results. Protein expression levels were quantified by densitometry normalized to the number of bacteria within each sample by using the ImageJ software.