Mechanism of uptake of deglucoteicoplanin amide derivatives across outer membranes of Escherichia coli and Pseudomonas aeruginosa

Abstract

Teicoplanin is a glycopeptide antibiotic which is ineffective against gram-negative bacteria because of its inability to penetrate the outer membrane. Removal of the sugar residues and attachment of polyamines to carbon 63 yielded two dibasic deglucoteicoplanin amides, MDL 62,766 (766) coli and P. aeruginosa outer membrane permeability to the hydrophobic fluorescent probe 1-N-phenylnaphthylamine (NPN), whereas the parent compounds teicoplanin aglycone and teicoplanin and the 13-lactam ceftazidime were totally ineffective. Addition of 1 mM Mg2+ blocked the increase in outer membrane permeability. Compound 766 had a lower MIC than 934 for both bacteria tested, bound to LPS with a higher affinity, and permeabilized outer membranes to NPN at lower concentrations. We propose that both deglucoteicoplanin amides exhibit increased gram-negative activity by virtue of their ability to access the self-promoted uptake pathway across the outer membrane.

Mechanism of Uptake of a Cationic Water-Soluble Pyridinium Zinc Phthalocyanine across the Outer Membrane of Escherichia coli

“…Since previous work revealed that it is the cell-bound PPC which is involved in the cell-killing process, the addition of Mg 2ϩ to the medium caused the observed "protective" effect by reducing the amount of the important cell-bound PPC (18). This protective effect also prevents the killing and alterations in outer membrane permeabilities of cells treated with many compounds, including polymyxin B, and causes increases in the MICs of some deglucoteicoplanin amide derivatives (11,13,31). The concentration of Mg 2ϩ required to antagonize the action of PPC appears to be slightly high at 10 to 20 mM, but there is no obvious explanation for this.…”

“…Since ampicillin and tetracycline (as the magnesium complex) are thought to enter the cell through the porins (5), any compound which crosses the outer membrane via the selfpromoted uptake pathway will have only slight effects upon the uptake of these compounds. Hancock and coworkers (7,(9)(10)(11)13) have shown extensively that many cationic compounds cause an increase in the level of uptake of a hydrophobic fluorophore, 1-N-phenylnaphthylamine. Crystal violet uptake and the detergent action of SDS are also enhanced by cationic compounds which are thought to enter the cell by the selfpromoted uptake pathway (12,33,35).…”

“…Little effect is seen on the sensitivity of the cells to hydrophilic compounds which cross the outer membrane via the porin pathway (9,24,31). This increase in outer membrane permeability also allows an increase in the uptake of the interacting compound itself (7,(9)(10)(11). Since the self-promoted uptake pathway involves interaction of the compounds at divalent cation binding sites, the presence of excess divalent cations, such as Mg 2ϩ , causes a competitive inhibition of binding and subsequent activity of the compounds (9-11, 13, 24, 31).…”

“…Compounds which interact at these sites by either chelating or displacing the divalent cation profoundly affect the structure and function of the outer membrane (7, 9-11, 24, 31). The size of the interacting compounds causes disorganization of the outer membrane and an increase in outer membrane permeability (7,(9)(10)(11). This increase in outer membrane permeability renders the bacterial cells more sensitive to compounds, generally hydrophobic in nature, such as various antibacterial agents, detergents, dyes, and steroid probes (7, 9-11, 13, 24, 31, 33-36).…”

“…An alternative mechanism postulated for the uptake of some compounds, many of which are cationic in nature, is the self-promoted uptake pathway (7,(9)(10)(11). Passage across the outer membrane via the self-promoted uptake pathway involves interaction of the compounds at the sites at which divalent cations cross-link adjacent LPS molecules (7,(9)(10)(11). Compounds which interact at these sites by either chelating or displacing the divalent cation profoundly affect the structure and function of the outer membrane (7, 9-11, 24, 31).…”