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Role of the outer membrane of Pseudomonas aeruginosa in antibiotic resistance Nicas, Thalia Ioanna


It was demonstrated that induction of a major outer protein, HI, was associated with increased resistance to chelators of divalent cations such as EDTA and to the cationic antibiotics polymyxins and aminoglycosides. Outer membrane protein HI was the major cellular protein in cells grown in Mg²⁺-deficient medium (0.02 mM Mg²⁺) and in mutants selected for resistance to polymyxin. Increase in protein HI was associated with decrease in cell envelope Mg²⁺. Induction of protein HI was prevented by supplementation of Mg²⁺-deficient medium with 0.5 mM Mg²⁺, Ca²⁺, Mn²⁺ or Sr²⁺, but not by Zn²⁺, Ba²⁺, or Sn²⁺. Cells grown in Ca²⁺, Mn²⁺ or Zn²⁺ showed enhanced levels of these cations as main major cell envelope associated cation. Only cells grown in the presence of those cations which failed to prevent HI induction were resistant to chelators, polymyxin B and gentamicin. Protein HI overproducing cells also demonstrated altered streptomycin uptake. It was further demonstrated that aminoglycosides could interact with the outer membrane so as to make it more permeable to other substances. Mg²⁺ inhibited aminoglycoside-mediated permeabilization. Both aminoglycosides and polymyxin B could be shown to displace a small amount of Mg²⁺ from the cell envelope.

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