ΔkatA biofilms exhibit increased antibiotic susceptibility. (A to C) Growth at 37°C was assessed by measurement of OD600 at hourly intervals for 18 h for the WT (black symbols) and ΔkatA mutant (white symbols) in the presence of increasing concentrations (micrograms per milliliter) of ampicillin (A), ceftriaxone (B), or ciprofloxacin (C). Error bars represent means ± SD for 6 technical replicates, and graphs are representative of at least 3 independent experiments. Data were analyzed by two-way ANOVA with Tukey’s test for multiple comparisons. (D to I) Biofilms were established by the WT and ΔkatA mutant for 20 h (D to F) or 4 h (G to I), followed by treatment with increasing concentrations of ampicillin (D and G), ceftriaxone (E and H), or ciprofloxacin (F and I) for an additional 20-h period. Each black (WT), white (ΔkatA mutant), and light gray (ΔkatA mutant plus bovine catalase) circle represents the number of CFU per milliliter recovered from an individual biofilm, and box and whisker plots display combined results from at least 3 independent experiments with at least 3 technical replicates each. *, P < 0.05; **, P < 0.01; ***, P < 0.001 (by two-way ANOVA with Sidak’s test for multiple comparisons).