FIG 4.

Mutants deficient in Psl biosynthesis (ΔpslA), the stringent response (ΔrelA ΔspoT), the membrane stress response (amgR), stationary-phase sigma factor regulation (ΔrpoS), and the glyoxylate shunt pathway (aceA) exhibit differential susceptibilities to ciprofloxacin in biofilms. The killing of wild-type (WT) and mutant P. aeruginosa strains in 3-day-old biofilms by ciprofloxacin was determined by viable plate counts. The dashed line delineates the killing of the WT bacteria, which resulted in a log reduction of 1.79 ± 0.43 (n = 15). Mutations that gave statistically significantly different log reductions are marked with asterisks (**, P < 0.01; *, P < 0.05).