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  • 1
    ISSN: 1617-4623
    Keywords: Key words ABC transporter ; Fluoroquinolone ; Multidrug resistance ; Mycobacteria ; Phosphate-specific transporter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phosphate-specific transporter (Pst) in bacteria is a multi-subunit system which belongs to the ABC family of transporters. The gene forms part of an operon and it is involved in phosphate uptake in prokaryotes. Its import function is known to be operative only under conditions of phosphate starvation. However, we found overexpression of this transporter in a Mycobacterium smegmatis strain selected for ciprofloxacin resistance (CIPr) which was grown under conditions in which the phosphate-scavenging function of this operon was inoperative. In CIPr cells, active efflux of the drug plays a predominant role in conferring high levels of fluoroquinolone resistance. We therefore investigated the role of this transporter in the process of efflux-mediated drug resistance by inactivating the pst operon in the CIPr strain. Phenotypic characterization of the resulting strain, CIPrd, showed a striking reduction in the minimal inhibitory concentration (MIC) of ciprofloxacin and in the drug extrusion profile as well. Genotype analysis, on the other hand, revealed partial disruption of the pst operon in CIPrd as a consequence of transporter gene amplification. Furthermore, disruption of this operon in wild-type cells resulted in hypersensitivity to ciprofloxacin and other xenobiotics to which CIPr cells exhibited cross-resistance. Thus our results provide strong evidence that Pst is a natural membrane transport system that has the ability to promote drug efflux in addition to its phosphate-scavenging function in the CIPr strain.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-3725
    Keywords: 12.38.-t ; 13.85.-t ; 13.87.Ce ; 13.87.Fh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of correlations between D and $${\overline D}$$ mesons produced in 500 GeV/cπ−-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed 791 ± 44 charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for different types of D meson pairs. We see slight correlations between the longitudinal momenta of the D and the $${\bar D}$$ , and significant correlations between the azimuthal angle of the D and the $${\bar D}$$ . The experimental distributions are compared to a next-to-leading-order QCD calculation and to predictions of the PYTHIA/JETSET Monte Carlo event generator. We observe less correlation between transverse momenta and different correlations between longitudinal momenta than these models predict for the default values of the model parameters. Better agreement between data and theory might be achieved by tuning the model parameters or by adding higher order perturbative terms, thus contributing to a better understanding of charm production. The relative production rates for the four sets of charm pairs, $$D^0{{\overline D}^0}, D^0 D^{-}, D^+{{\overline D}^0}, D^+ D^{-}$$ as calculated in the PYTHIA/JETSET event generator with the default parameters, agree with data as far as the relative ordering, but predict too many $$D^+ {{\overline D}^0}$$ pairs and too few $$D^+ D^{-}$$ pairs.
    Type of Medium: Electronic Resource
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