Outer membrane permeability of non-typable Haemophilus influenzae

Preliminary studies of the 2D crystallization of Omp1 of Serratia marcescens: observation by atomic force microscopy in native membranes environment and reconstituted in proteolipid sheets

In this work the porin Omp1 of Serratia marcescens was expressed in a porin deficient mutant (Escherichia coli UH302) and its functionality studied following the accumulation of ciprofloxacin in bacteria. The protein was extracted, purified and reconstituted in proteoliposomes of different composition (lipopolysaccharide (LPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)). Maximum extraction of the detergent was achieved applying different steps of dialysis and centrifugation. Proteolipid sheets with different composition were spread onto mica and observed by atomic force microscopy. Two-dimensional crystal of Omp1 was not observed in any case due to low resolution achieved. Judging from the images features POPC is the most suitable phospholipid to enhance 2D lattice formation for Omp1.

The role of Serratia marcescens porins in antibiotic resistance

The outer membrane permeability of Serratia marcescens was studied by comparing porin-deficient mutants with their parental strains. Omp1-deficient strains were selected by moxalactam resistance, whereas mutants lacking the Omp2 porin were obtained by experimental infection with the SMP2 phage, whose primary receptor is the Omp2 porin. The role of porins was demonstrated in quinolone accumulation assays, where semiquantitative differences in accumulation were observed. Permeability coefficients to cephaloridine of Omp1 mutants were determined and compared with those of the parental strain. The clinical isolates S. marcescens HCPR1 and 866 showed 30- to 200-fold reduced permeability coefficients when Omp1 porin was absent.

The acrAB homolog of Haemophilus influenzae codes for a functional multidrug efflux pump

Disruption of gene HI0894 or HI0895 in Haemophilus influenzae Rd, homologs of Escherichia coli acrAB multidrug efflux genes, caused hypersusceptibility to erythromycin, rifampin, novobiocin, and dyes such as ethidium bromide and crystal violet and increased accumulation of radioactive erythromycin, showing that these genes are expressed and contribute to the baseline level resistance of this organism through active drug efflux. The gene disruption did not produce detectable changes in susceptibility to several other antibiotics, possibly because rapid influx of small antibiotic molecules through the large H. influenzae porin channels counterbalances their efflux.