Fig 3.

The MexAB-OprM or MexEF-OprN efflux pumps contribute to the tolerance of P. aeruginosa biofilms to antimicrobial agents. P. aeruginosa PAO1, the ΔbrlR mutant, and PAO255 (inactivated in mexAB-oprM and mexEF-oprN) were grown for 1 day as biofilms and subsequently treated for 1 h with tobramycin (150 μg/ml; Tob), kanamycin (150 μg/ml; Km), trimethoprim (150 μg/ml; Trim), tetracycline (100 μg/ml; Tet), and norfloxacin (450 μg/ml; Nor). *, significantly different from the values for the P. aeruginosa ΔbrlR mutant (P ≤ 0.01). Experiments were carried out at least three times. Error bars denote standard deviations.