Quantitative assessment of biofilm development by clinical pneumococcal isolates. Fig. 2A. Biofilm development by clinical isolates at days 1, 3 and 6 of culture on polystyrene plates as shown by viable adherent cells (CFUs/cm2). Points represent an average of three duplicate wells per time point in two independent experiments. Error bars represent SD. Fig. 2B. Biofilm development (initial attachment) assayed by crystal violet absorbance comparing 6 clinical pneumococcal isolates on polystyrene over 24 hours. Bars show average triplicate samples of 5 independent experiments. Bars represent SD. Fig. 2C. COMSTAT assessment of pneumococcal biofilm development after 6 days of culture. Two parameters of surface attached pneumococci are shown: maximum thickness (biofilm towers) (left axis) and biomass (biofilm volume) (right axis). Bars represent an average of 3–5 images taken from duplicate plates in 2 independent experiments (minimum n = 12). Error bars represent standard error of the mean. Fig. 2D. Biofilm forming index (BFI) of the 6 pneumococcal clinical strains (serotype in parentheses) combining statistical analyses from the widely used biofilm assays: CFU/cm2, CV assay and COMSTAT analysis. The index ranks each strain according to biofilm formation.