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  • 1
    Electronic Resource
    Electronic Resource
    A novel assembly process of the multicomponent xenobiotic efflux pump in Pseudomonas aeruginosa (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 46 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nfxC-type cells of Pseudomonas aeruginosa show resistance to a wide range of structurally and functionally diverse antibiotics, which is a phenomenon that is mainly attributable to the expression of the MexEF-OprN xenobiotic transporter. The MexF, MexE and OprN subunits of this transporter are located on the inner membrane, the periplasm and the outer membrane, respectively, and are assumed to function as an energy-dependent transporter, a bridge connecting the inner and outer membranes and outer membrane channel respectively. The nfxC-type cells showed a single protein band of MexF and OprN, whereas MexE appeared as three distinct bands in an SDS-polyacrylamide gel electrophoretogram. The mutant cells lacking MexF produced undetectable OprN and only a full-size of MexE even though the cells had unimpaired oprN and mexE. Expression of the plasmid-borne MexF in this mutant fully restored OprN and three MexE bands. Another class of mutants producing a full amount of MexF yielded undetectable OprN and two MexE bands lacking the smallest protein species suggesting that the presence of the smallest MexE subunit is required for stabilization of OprN. To identify which part of MexE was needed for stabilization and assembly of OprN, the carboxyl-terminal-truncated MexE tagged with polyhistidine was constructed and protein bands were visualized in the presence of MexF with an antibody raised against polyhistidine or MexE. The results revealed that the proteolytic processing of MexE would occur at carboxyl terminal amino acids between 11 and 16, thereby suggesting that the presence of the C-terminal truncated MexE is essential for stabilization and the proper assembly of OprN. Nucleotide sequencing of mutant mexFs, which produce a wild-type level of MexF but are unable to support the production of the smallest MexE, thereby destabilizing OprN, revealed that all the mutations were located within two large periplasmic domains of MexF between transmembrane segments 1–2 and 7–8. Taking these findings together, we concluded that two large periplasmic domains of MexF interact with MexE thereby promoting programmed processing of MexE, and this complex eventually assists the correct assembly and sorting of OprN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03197.x
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  • 2
    Electronic Resource
    Electronic Resource
    MexZ-mediated regulation of mexXY multidrug efflux pump expression in Pseudomonas aeruginosa by binding on the mexZ-mexX intergenic DNA (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 238 (2004), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: MexZ is a transcriptional regulator of the mexXY multidrug transporter operon, which confers aminoglycoside resistance on Pseudomonas aeruginosa. Highly purified MexZ showed direct binding with a specific site of the mexZ-mexX intergenic DNA when probed by a gel retardation assay. Both in vitro chemical cross-linking experiments and an in vivo two-hybrid expression system showed that the active form of MexZ, which is capable of binding the intergenic DNA, appeared to be a dimer. These results explain the mechanism by which MexZ represses transcription of the mexXY operon, but do not explain the substrate-induced hyperproduction of MexXY. The presence of inducer antibiotic in the gel-retardation assay mixture failed to detect altered MexZ-probe DNA interaction suggesting the possible involvement of an additional regulator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2004.tb09732.x
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular mechanism of MexR-mediated regulation of MexAB–OprM efflux pump expression in Pseudomonas aeruginosa (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 195 (2001), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: To elucidate the molecular mechanism by which the MexR repressor regulates expression of the MexAB–OprM efflux pump, we investigated MexR and the mexR–mexA intergenic DNA (mexOP) interaction, and transcription of the mexA–lacZ reporter gene containing different lengths of mexOP. Homogeneously purified MexR bound specifically to mexOP proximal to mexR. The mexOP–lacZ fusion gene lacking the region immediately proximal to mexR showed minimum enzyme activity, thereby suggesting that a promoter element is located between mexR and the MexR-binding sites. These observations explain the mechanism of self-regulation of mexR expression as well as low and elevated expression of MexAB–OprM in the wild-type strain and nalB-type mutant, respectively, of Pseudomonas aeruginosa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2001.tb10492.x
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  • 4
    Electronic Resource
    Electronic Resource
    Variation of the mexT gene, a regulator of the MexEF-OprN efflux pump expression in wild-type strains of Pseudomonas aeruginosa (2000)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 192 (2000), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We found three variations of wild-type strains in terms of mexT-mediated regulation of the MexEF-OprN efflux pump, in which overexpression of the pump results in nfxC-type antibiotic resistance in Pseudomonas aeruginosa. Type-I: the mexT gene of the wild-type strain encoded inactive MexT and the nfxC-type mutants derived from this parent had an additional mutation in mexT converting MexT from the inactive to the active form. Type-II: The mexT gene in the wild-type strain had an 8-bp insert producing inactive MexT and the nfxC-type mutants from this parent had a deletion of the 8-bp insert converting inactive MexT to the active form. Type-III: Both the wild-type strain and its nfxC-type derivative produced identical and active MexT. The nfxC mutant from this parent must have an additional mutation. The original nfxC mutant isolated in 1990 might be derived from the Type-I parent strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2000.tb09367.x
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  • 5
    Electronic Resource
    Electronic Resource
    Antibiotic stress induces a large amount of outer membrane protein in Pseudomonas aeruginosa (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 165 (1998), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: To investigate the bacterial response to antibiotic stress, we analyzed the outer membrane proteins of Pseudomonas aeruginosa grown in the presence of a sub-minimum inhibitory concentration of antibiotics. Among the antibiotics tested, fluoroquinolones and streptonigrin induced a large amount of outer membrane protein with a molecular mass of 43 kDa. This protein is most likely the stress-responsive protein, since the quinolone-resistant mutants with a higher minimum inhibitory concentration of antibiotic than the wild-type strain produced a large amount of 43-kDa protein only in the presence of sub-minimum inhibitory concentration of the mutants itself, but not that of the antibiotic-susceptible wild-type strain. The sequence of N-terminal 15 amino acids of the 43-kDa protein was identical to that of pyocin R1. However, purified pyocin R1 failed to accumulate in the outer membrane. Thus, we concluded that the 43-kDa protein (pyocin R1) is the antibiotic-stress-induced outer membrane protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1998.tb13155.x
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  • 6
    Electronic Resource
    Electronic Resource
    El Tor hemolysin of Vibrio cholerae O1 forms channels in planar lipid bilayer membranes (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 150 (1997), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We investigated the channel formation by El Tor hemolysin (molecular mass, 65 kDa) of Vibrio cholerae O1 biotype El Tor in planar lipid bilayers. The El Tor hemolysin channel exhibited asymmetric and hyperbolic membrane current with increasing membrane potential, meaning that the channel is voltage dependent. The zero-current membrane potential measured in KCl solution showed that permeability ratio PK+/PCl− was 0.16, indicating that the channel is 6-fold more anion selective over cation. The hemolysin channel frequently flickered in the presence of divalent cations, suggesting that the channel spontaneously opens and closes. These data imply that the El Tor hemolysin damages target cells by the formation of transmembrane channels and, consequently, is the cause of osmotic cytolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1997.tb10377.x
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  • 7
    Electronic Resource
    Electronic Resource
    nalB-type mutations causing the overexpression of the MexAB-OprM efflux pump are located in the mexR gene of the Pseudomonas aeruginosa chromosome (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 179 (1999), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Two mutations, one at the nalB and the other at the mexR locus, in the Pseudomonas aeruginosa chromosome are known to cause overexpression of the MexAB-OprM efflux pump. Based on the following results, we concluded that nalB is the mutation that has occurred within the mexR gene of the P. aeruginosa chromosome. (i) Nucleotide sequencing of the mex operon upstream region of 21 independent nalB-type mutants including the original nalB9 revealed that all the mutations were located within the mexR gene. The mutations were classified into three different groups and nine types including single base substitutions, single base deletions and base insertions. (ii) Substitution of the mutant mexR with the wild-type mexR and replacement of the wild-type mexR with a defined mexR mutation resulted in the expression of wild-type and nalB-type MexAB-OprM respectively, which was confirmed by testing the antibiotic susceptibility and β-galactosidase activity of the mexA-lacZ translational fusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1999.tb08709.x
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  • 8
    Electronic Resource
    Electronic Resource
    The barrier function of the outer membrane of Pseudomonas maltophilia in the diffusion of saccharides and β-lactam antibiotics (1989)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 60 (1989), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract This paper reports that the efficiency of solute diffusion throgh the outer membrane of Pseudomonas maltophilia is roughly 3 to 5% of that of Escherichia coli. This is despite the fact that the outer membrane pore(s) is only a little smaller than that of E. coli. These results suggest that P. maltophilia has a low copy number of porin(s). The outer membrane of antibiotic resistant clinical isolates showed even less efficient permeability towards saccharides and antibiotics than the laboratory strains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1989.tb03424.x
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  • 9
    Electronic Resource
    Electronic Resource
    Outer membrane permeability of β-lactamase inhibitors in Pseudomonas aeruginosa (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 129 (1995), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Evaluation of four β-lactamase inhibitors in terms of their outer membrane permeability in Pseudomonas aeruginosa revealed that sulbactam and tazobactam diffused most efficiently and equally well. That of BRL42715 appeared to be a factor of ten lower than that of the above two, but it showed the strongest β-lactamase inhibitory activity. This is most likely due to its better β-lactamase inactivating activity. BRL42715 at 1.56 μg ml−1 lowered the minimum inhibitory concentrations of ceftazidime and imipenem in a strain producing fully derepressed β-lactamase and an undetectable level of the outer membrane protein OprD2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1995.tb07588.x
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  • 10
    Electronic Resource
    Electronic Resource
    Factors that influence the permeability assay of the outer membrane of Pseudomonas aeruginosa (1991)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 80 (1991), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: Brief exposure of Pseudomonas aeruginosa to a temperature of 10°C or lower caused a significant leakage of the periplasmic β-lactamase into the medium. The extent of leakage increased as the incubation temperature was lowered to 4°C and reached a maximum at 0°C. Cells grown in the presence of β-lactamase inducers were unsuitable for the permeability assay. It was found that the diffusion rates of β-lactams through the outer membrane of P. aeruginosa were much lower than those previously reported, as assayed under refined conditions. The diffusion rates of β-lactams in one of the mutants tested were an order of magnitude lower than those of the other strains, despite the fact that the outer membrane protein profile of the strain appeared to be indistinguishable from those of the others. These results suggest that β-lactam antibiotics diffuse through the outer membrane of P. aeruginosa, at least partly, through a non-porin pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1991.tb04686.x
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