We have characterized a nonlethal selection for mutations that allow Escherichia coli to grow on large maltodextrins (Dex+) in the absence of the lamB encoded maltoporin LamB. These Dex+ mutations occur before and after imposition of the selection and the selection does not result in a general increase in mutagenesis. The recovered Dex+ mutations are almost exclusively mutations that alter the ...

Bacterial resistance is a critical public health issue and the development of alternative antibiotics to counteract this problem is an urgent matter. Fluoroquinolones are widely used antibiotics and numerous cases of bacterial resistance to these drugs have already been reported. One important mechanism of resistance is the decrease of the permeability of the bacterial membrane to antibiotics b...

We performed transposon mutagenesis of a two-color fluorescent reporter strain to identify new regulators of the porin genes ompF and ompC in Escherichia coli. Screening of colonies by fluorescence microscopy revealed numerous mutants that exhibited interesting patterns of porin expression. One mutant harbored an insertion in the gene encoding the histidine kinase CpxA, the sensor for a two-com...

We investigated the mechanism of imipenem resistance in Enterobacter aerogenes strain 810, a clinical isolate from the United States for which the imipenem MIC was 16 micro g/ml and the meropenem MIC was 8 micro g/ml. An imipenem-susceptible revertant, strain 810-REV, was obtained after multiple passages of the strain on nonselective media. For the revertant, the imipenem MIC was </=1 micro g/m...

We have generated a mutant form of the OmpR regulatory protein, OmpRD55E, that is active independent of the EnvZ kinase. Notably, the pattern of OmpF and OmpC expression can be altered simply by changing the level of this mutant protein in the cell. This result supports a key prediction of the current model of porin regulation, which states that the differential regulation of OmpF and OmpC is a...

Escherichia coli cells lacking the histone-like protein HU form filaments and have an abnormal number of anucleate cells. Furthermore, their phenotype resembles that of rfa mutants, the well-characterized deep-rough phenotype, as they show an enhanced permeability that renders them hypersensitive to chloramphenicol, novobiocin, and detergents. We show that, unlike rfa mutants, hupAB mutants do ...

Structure and function of many transmembrane proteins are affected by their environment. In this respect, reconstitution of a membrane protein into a biomimetic polymer membrane can alter its function. To overcome this problem we used membranes formed by poly(1,4-isoprene-block-ethylene oxide) block copolymers blended with 1,2-diphytanoyl-sn-glycero-3-phosphocholine. By reconstituting the outer...

Avian pathogenic Escherichia coli is an important pathogen causes systemic infections in avian species and large economic losses in poultry industry worldwide. The functional role of porins during the infection and their mechanisms of interaction with host tissues for adhesion to and invasion are poorly understood. However, whether porins play a role in infection remains unclear. In this study ...

Many Gram-negative bacterial pathogens express contact-dependent growth inhibition (CDI) systems that promote cell-cell interaction. CDI+ bacteria express surface CdiA effector proteins, which transfer their C-terminal toxin domains into susceptible target cells upon binding to specific receptors. CDI+ cells also produce immunity proteins that neutralize the toxin domains delivered from neighbo...