Compounds which increase the permeability of the Pseudomonas aeruginosa outer membrane

Hydrolysis of the chromogenic beta-lactam nitrocefin by periplasmic beta-lactamase in intact Pseudomonas aeruginosa cells was used to assess the influence of various compounds on the permeability of the P. aeruginosa outer membrane. In addition to the five previously described outer membrane-active compounds EDTA, polymyxin B, gentamicin, poly-L-lysine, and Tris, seven other compounds were shown to increase outer membrane permeability to nitrocefin by 14- to 63-fold. These other compounds included poly-L-ornithine, neomycin, cetyltrimethylammonium bromide, nitrilotriacetate, L-ascorbate, and acetylsalicylate. In each case, Mg2+ ions antagonized, to different extents, the enhancement of outer membrane permeability. The same compounds increased the permeability of the outer membrane to the protein lysozyme and to the hydrophobic fluorescent probe 1-N-phenylnaphthylamine, although L-ascorbate and acetylsalicylate showed only very weak enhancement of uptake in these assays. In this report, we discuss the possibility that these compounds act at a common outer membrane site at which divalent cations noncovalently cross-bridge adjacent lipopolysaccharide molecules.