The MerR-Like Transcriptional Regulator BrlR Contributes to Pseudomonas aeruginosa Biofilm Tolerance

Abstract

ABSTRACTBiofilms are composed of surface-attached microbial communities. A hallmark of biofilms is their profound tolerance of antimicrobial agents. While biofilm drug tolerance has been considered to be multifactorial, our findings indicate, instead, that bacteria within biofilms employ a classical regulatory mechanism to resist the action of antimicrobial agents. Here we report that the transcriptional regulator BrlR, a member of the MerR family of multidrug transport activators, plays a role in the high-level drug tolerance of biofilms formed byPseudomonas aeruginosa. Expression ofbrlRwas found to be biofilm specific, withbrlRinactivation not affecting biofilm formation, motility, orpslAexpression but increasingndvBexpression. Inactivation ofbrlRrendered biofilms but not planktonic cells grown to exponential or stationary phase significantly more susceptible to hydrogen peroxide and five different classes of antibiotics by affecting the MICs and the recalcitrance of biofilms to killing by microbicidal antimicrobial agents. In contrast, overexpression ofbrlRrendered both biofilms and planktonic cells more tolerant to the same compounds.brlRexpression in three cystic fibrosis (CF) isolates was elevated regardless of the mode of growth, suggesting a selection for constitutivebrlRexpression uponin vivobiofilm formation associated with chronic infections. Despite increasedbrlRexpression, however, isolate CF1-8 was as susceptible to tobramycin as was a ΔbrlRmutant because of a nonsense mutation inbrlR. Our results indicate for the first time that biofilms employ a specific regulatory mechanism to resist the action of antimicrobial agents in a BrlR-dependent manner which affects MIC and recalcitrance to killing by microbicidal antimicrobial agents.