Disrupting the spatio-temporal symmetry of the electron dynamics in atmospheric pressure plasmas by voltage waveform tailoring.

Single frequency, geometrically symmetric Radio-Frequency (rf) driven atmospheric pressure plasmas exhibit temporally and spatially symmetric patterns of electron heating, and consequently, charged particle densities and fluxes. Using a combination of phase-resolved optical emission spectroscopy and kinetic plasma simulations, we demonstrate that tailored voltage waveforms consisting of multiple rf harmonics induce targeted disruption of these symmetries. This confines the electron heating to small regions of time and space and enables the electron energy distribution function to be tailored.

Propyl paraben induces potassium efflux in Escherichia coli.

Objectives: Parabens are currently used as antibacterial preservatives in pharmaceutical, cosmetic and food products but there are no precise data concerning their activity on bacterial membranes.

Methods: We analysed the cytoplasmic potassium release during propyl paraben addition by using a selective electrode. Various conditions were assayed to investigate the bacterial paraben susceptibility.

Beta-lactam screening by specific residues of the OmpF eyelet.

Beta-lactams use aqueous channels of porins to penetrate Gram-negative bacteria. The L3 loop of Escherichia coli OmpF porin is a key feature that actively contributes to both channel size and electrostatic properties. Acid residues D113, E117, and D121 are responsible for the negative part of the local electrostatic field on this loop.

Inhibitors of antibiotic efflux in resistant Enterobacter aerogenes and Klebsiella pneumoniae strains.

In Enterobacter aerogenes and Klebsiella pneumoniae, efflux provides efficient extrusion of antibiotics and contributes to the multidrug resistance phenotype. One of the alkoxyquinoline derivatives studied here, 2,8-dimethyl-4-(2'-pyrrolidinoethyl)-oxyquinoline, restores noticeable drug susceptibility to resistant clinical strains. Analyses of energy-dependent chloramphenicol efflux indicate that this compound inhibits the efflux pump mechanism and improves the activity of structurally unrelated antibiotics on multidrug-resistant E.

Colicins, spermine and cephalosporins: a competitive interaction with the OmpF eyelet.

The L3 loop is an important feature of the OmpF porin structure, contributing to both channel size and electrostatic properties. Colicins A and N, spermine, and antibiotics that use OmpF to penetrate the cell, were used to investigate the structure-function relationships of L3. Spermine was found to protect efficiently cells expressing wild-type OmpF from colicin action.

Alteration of pore properties of Escherichia coli OmpF induced by mutation of key residues in anti-loop 3 region.

The Escherichia coli OmpF pore is governed by an internal constriction consisting of the negatively charged loop 3 folded into the lumen and the positively charged barrel wall located on the opposite side across the pore, 'anti-loop 3'. To investigate the role of anti-loop 3 in solute diffusion, four site-directed mutations, K16A, K16D, R132A and R132D, were introduced into this eyelet region. The mutant porins were expressed efficiently and inserted into the outer membrane, and the thermal stabilities of the resulting trimers were determined.