The permeability of the outer membrane of Escherichia coli to hydrophilic compounds is controlled by porin channels. Electrophysiological experiments showed that polyamines inhibit ionic flux through cationic porins when applied to either side of the membrane. Externally added polyamines, such as cadaverine, decrease porin-mediated fluxes of beta-lactam antibiotics in live cells. Here we tested...

BACKGROUND AND PURPOSE In addition to beta-lactamase production, loss of porins confers resistance to extended-spectrum beta-lactams in Klebsiella pneumoniae and Escherichia coli infection. This study describes the detection of SHV-12 extended-spectrum beta-lactamase (ESBL) subtype and the loss of OmpK35 porin in 4 strains of K. pneumoniae and E. coli. METHODS Isoelectric focusing was perform...

Carbapenems such as imipenem and meropenem are not rapidly hydrolyzed by commonly occurring beta-lactamases. Nevertheless, it was possible, by mutagenesis and selection, to isolate mutant strains of Enterobacter cloacae and Proteus rettgeri that are highly resistant to meropenem and imipenem. Two alterations were noted in the E. cloacae mutants. First, the mutant strains appeared to be strongly...

Two clinical isolates of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae were noted to be less susceptible than expected to imipenem. Both were missing outer membrane proteins that serve as channels for antibiotic entry. The role of beta-lactamase in resistance was investigated by eliminating the original ESBL and introducing plasmids encoding various ESBLs and AmpC beta...

Clinical isolates of Klebsiella pneumoniae resistant to carbapenems are being isolated with increasing frequency. Loss of the expression of the major nonspecific porins OmpK35/36 is a frequent feature in these isolates. In this study, we looked for porins that could compensate for the loss of the major porins in carbapenem-resistant organisms. Comparison of the outer membrane proteins from two ...

Helicobacter pylori is a causative agent of gastritis in humans and is correlated with gastric ulcer formation. Infections with this bacterium have proven difficult to treat with antimicrobial agents. To better understand how this bacterium transports compounds such as antimicrobial agents across its outer membrane, identification of porin proteins is important. We have recently identified a fa...

The mitochondrial porin or VDAC (Voltage-Dependent Anion Channel), the pore-forming structure responsible for the high permeability of the outer mitochondrial membrane, was found to be one of only three mitochondrial proteins bound by [14C]dicyclohexylcarbodiimide (DCCD) at low dosages (1.5 nmol/mg of mitochondrial porin) (De Pinto, V., Tommasino, M., Benz, R., and Palmieri, F. (1985) Biochim. ...

The outer membrane (OM) of Gram-negative bacteria is an unusual asymmetric bilayer with an external monolayer of lipopolysaccharide (LPS) and inner layer of phospholipids. The LPS layer is rigid and stabilized by divalent cation crosslinks between phosphate groups on the core oligosaccharide regions. This means that the OM is robust and highly impermeable to toxins and antibiotics. During their...

The neisserial porin P.I is a GTP binding protein that forms a voltage-gated channel that translocates into mammalian cell membranes and modulates host cell signaling events. Here, we report that P.I confers invasion of the bacterial pathogen Neisseria gonorrhoeae into Chang epithelial cells and that this event is controlled by GTP, as well as other phosphorus-containing compounds. Bacterial in...

OmpF and OmpC porins were differentially regulated by nutrient limitation and growth rate in glucose- or nitrogen-limited chemostat cultures of Escherichia coli. Transcriptional and translational ompF fusions showed a sharp peak of expression under glucose limitation at D = 0.3 h-1, with lower amounts at lower and higher growth rates. The peak of OmpR-dependent transcriptional stimulation of om...