Secondary multidrug efflux pump mutants alter Escherichia coli biofilm growth in the presence of cationic antimicrobial compounds

Escherichia coli possesses many secondary active multidrug resistance transporters (MDTs) that confer overlapping substrate resistance to a broad range of antimicrobials via proton and/or sodium motive force. It is uncertain whether redundant MDTs uniquely alter cell survival when cultures grow planktonically or as biofilms. In this study, the planktonic and biofilm growth and antimicrobial resistance of 13 E. coli K-12 single MDT gene deletion strains in minimal and rich media were determined. Antimicrobial tolerance to tetracycline, tobramycin and benzalkonium were also compared for each Delta MDT strain. Four E. coli MDT families were represented in this study: resistance nodulation and cell division members acrA, acrB, acrD, acrE, acrF and to1C; multidrug and toxin extruder mdtK; major facilitator superfamily emrA and emrB; and small multidrug resistance members emrE, sugE, nicht and mdtJ. Deletions of multipartite efflux system genes acrB, acrE and to/C resulted in significant reductions in both planktonic and biofilm growth phenotypes and enhanced antimicrobial susceptibilities. The loss of remaining MDT genes produced similar or enhanced (acrD, acrE, emrA, emrB, mdtK, emrE and mdtJ) biofilm growth and antimicrobial resistance. Delta MDT strains with enhanced antimicrobial tolerance also enhanced biofilm biomass. These findings suggest that many redundant MDTs regulate biofilm formation and drug tolerance. (C) 2016 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.