FIG 3 .

Polymicrobial biofilm formation protects H. influenzae and M. catarrhalis from antibiotic treatment. Single-species or polymicrobial stationary biofilms were established for 4 h and treated with 60 µg/ml trimethoprim-sulfamethoxazole (TS) (A) or 6 µg/ml clarithromycin (B) for 24 h. Biofilms were resuspended in sterile PBS, serially diluted, and plated on sBHI medium plus clarithromycin or BHI medium for enumeration of viable H. influenzae and M. catarrhalis bacteria, respectively. Data are represented as the mean results from three combined experiments, with two replicates per experiment. Error bars represent SEM. *, P < 0.05.