The hydrophobic uptake pathway across the outer membrane of the antibiotic supersusceptible Pseudomonas aeruginosa mutant Z61

Abstract The Pseudomonas aeruginosa antibiotic supersusceptible mutant Z61 was 50–400-fold more susceptible than its wild-type parent K799 to 5 hydrophobic antibiotics. The strain Z61 outer membrane also demonstrated enhanced permeability towards a hydrophobic fluorescent probe. Strain Z61 cells had an altered cell surface, as revealed by phase-partitioning experiments, a lower amount of Lipid A phosphate, and a reduction in the number of Mg²⁺ binding sites in Lipid A, as demonstrated by dansyl polymyxin competition experiments. An antibiotic permation pathway directly through the outer membrane bilayer, rather than through porin proteins, is proposed for strain Z61.