FIG 6.

Antibiotic sensitivity varies by antibiotic and medium type. (A, B, and C) Relative CFU of 6-day-old biofilms and planktonic cells from the same wells after 48 h of treatment with a range of antibiotic concentrations in 3 media. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; n.s., P > 0.05 by Student's t test. (D) LD₉₀ (dose required to kill 90% of the cells) analysis of the data from panels A, B, and C. Bars with hatched lines indicate that we were unable to observe killing of 90% of the population at any concentration used, and so the LD₉₀ is >200 μg/ml. The LD₉₀ was calculated for each replicate, and the bars indicate means and standard deviations.