FIG 4.

Susceptibility phenotype of dispersed cells obtained in response to exposure of P. aeruginosa PAO1 biofilms to NO. (A) Absorbance of biofilm tube reactor effluents after the induction of dispersion by sodium nitroprusside, with sodium nitroprusside serving as a source of nitric oxide (NO). Cells that were collected for subsequent experiments and referred to as “NO-induced dispersed cells” are indicated by shaded boxes. Effluents of untreated biofilms were used as a control. (B) Susceptibility of biofilm cells, NO-induced dispersed cells, and planktonic cells grown to exponential and stationary phases to colistin (20 μg/ml) after exposure for 1 h at 37°C. Colistin susceptibility is expressed as log₁₀ reduction in CFU. All experiments were repeated at least 3 times. Error bars indicate standard deviations. *, Significantly different from biofilms (P < 0.01 as determined by ANOVA and SigmaStat). Exp, exponential phase; Stat, stationary phase.