Reviving Antibiotics: Efflux Pump Inhibitors That Interact with AcrA, a Membrane Fusion Protein of the AcrAB-TolC Multidrug Efflux Pump

To understand better the mechanisms of fluoroquinolone resistance in Enterococcus faecalis, fluoroquinolone-resistant mutants isolated from Ent. faecalis ATCC 29212 by stepwise selection with sparfloxacin (SPX) and norfloxacin (NOR) were analysed. The results showed the following. (i) In general, fluoroquinolone-resistance mechanisms in Ent. faecalis are similar to those in other Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus pneumoniae, namely, mutants with amino acid changes in both GyrA and ParC exhibited high fluoroquinolone resistance, and single GyrA mutants and a single ParC mutant were more resistant to SPX and NOR, respectively, than the parent strain, indicating that the primary targets of SPX and NOR in Ent. faecalis are DNA gyrase and topoisomerase IV, respectively. (ii) Alterations in GyrB (ΔKGA, residues 395–397) and ParE (Glu-459 to Lys) were associated with fluoroquinolone resistance in some mutants. Moreover, the facts that the NOR MIC, but not the SPX MIC, decreased in the presence of multidrug efflux pump inhibitors, that NOR accumulation decreased in the cells, and that the EmeA mRNA expression level did not change, strongly suggested that a NorA-like efflux pump, rather than EmeA, was involved in resistance to NOR.

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Substrate-Dependent Utilization of OprM or OpmH by the Pseudomonas aeruginosa MexJK Efflux Pump

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.49.5.2133-2136.2005 ◽

2005 ◽

Vol 49 (5) ◽

pp. 2133-2136 ◽

Cited By ~ 30

Author(s):

Rungtip Chuanchuen ◽

Takeshi Murata ◽

Naomasa Gotoh ◽

Herbert P. Schweizer

Keyword(s):

Pseudomonas Aeruginosa ◽

Cell Division ◽

Membrane Proteins ◽

Fusion Protein ◽

Membrane Fusion ◽

Outer Membrane ◽

Protein Pair ◽

Efflux Pump ◽

Outer Membrane Proteins ◽

Membrane Fusion Protein

ABSTRACT MexJK requires OprM for erythromycin efflux but not for triclosan efflux. Deletion of 15 OprM family outer membrane proteins (OMPs) revealed that only the TolC homolog OpmH functions with MexJK for triclosan efflux. This is the first report of natural utilization of multiple OMPs by a given resistance nodulation cell division transporter/membrane fusion protein pair.

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BpeAB-OprB, a Multidrug Efflux Pump in Burkholderia pseudomallei

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.48.4.1128-1135.2004 ◽

2004 ◽

Vol 48 (4) ◽

pp. 1128-1135 ◽

Cited By ~ 68

Author(s):

Y. Y. Chan ◽

T. M. C. Tan ◽

Y. M. Ong ◽

K. L. Chua

Keyword(s):

Membrane Protein ◽

Burkholderia Pseudomallei ◽

Antimicrobial Agents ◽

Efflux Pump ◽

Multidrug Efflux ◽

Multidrug Efflux Pump ◽

Efflux Pump Inhibitor ◽

Membrane Fusion Protein ◽

Wide Range ◽

Inner Membrane Protein

ABSTRACT Burkholderia pseudomallei, the causative agent of melioidosis, is intrinsically resistant to a wide range of antimicrobial agents, including β-lactams, aminoglycosides, macrolides, and polymyxins. An operon, bpeR-bpeA-bpeB-oprB, which encodes a putative repressor, a membrane fusion protein, an inner membrane protein, and an outer membrane protein, respectively, of a multidrug efflux pump of the resistance-nodulation-division family was identified in B. pseudomallei. The divergently transcribed bpeR gene encodes a putative repressor protein of the TetR family which probably regulates the expression of the bpeAB-oprB gene cluster. Comparison of the MICs and minimal bactericidal concentrations of antimicrobials for bpeAB deletion mutant KHWΔbpeAB and its isogenic wild-type parent, KHW, showed that the B. pseudomallei BpeAB-OprB pump is responsible for the efflux of the aminoglycosides gentamicin and streptomycin, the macrolide erythromycin, and the dye acriflavine. Antibiotic efflux by the BpeAB-OprB pump was dependent on a proton gradient and differs from that by the AmrAB-OprA pump in that it did not efflux the aminoglycoside spectinomycin or the macrolide clarithromycin. The broad-spectrum efflux pump inhibitor MC-207,110 did not potentiate the effectiveness of the antimicrobials erythromycin and streptomycin in B. pseudomallei.

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Chimeric Analysis of AcrA Function Reveals the Importance of Its C-Terminal Domain in Its Interaction with the AcrB Multidrug Efflux Pump

Journal of Bacteriology ◽

10.1128/jb.185.18.5349-5356.2003 ◽

2003 ◽

Vol 185 (18) ◽

pp. 5349-5356 ◽

Cited By ~ 74

Author(s):

Christopher A. Elkins ◽

Hiroshi Nikaido

Keyword(s):

Antimicrobial Agents ◽

Efflux Pump ◽

Small Region ◽

Terminal Segment ◽

Multidrug Efflux ◽

Multidrug Efflux Pump ◽

Functional Protein ◽

Membrane Fusion Protein ◽

C Terminus ◽

Resistance Nodulation Division

ABSTRACT AcrAB-TolC is the major, constitutively expressed efflux protein complex that provides resistance to a variety of antimicrobial agents in Escherichia coli. Previous studies showed that AcrA, a periplasmic protein of the membrane fusion protein family, could function with at least two other resistance-nodulation-division family pumps, AcrD and AcrF, in addition to its cognate partner, AcrB. We found that, among other E. coli resistance-nodulation-division pumps, YhiV, but not MdtB or MdtC, could also function with AcrA. When AcrB was assessed for the capacity to function with AcrA homologs, only AcrE, but not YhiU or MdtA, could complement an AcrA deficiency. Since AcrA could, but YhiU could not, function with AcrB, we engineered a series of chimeric mutants of these proteins in order to determine the domain(s) of AcrA that is required for its support of AcrB function. The 290-residue N-terminal segment of the 398-residue protein AcrA could be replaced with a sequence coding for the corresponding region of YhiU, but replacement of the region between residues 290 and 357 produced a protein incapable of functioning with AcrB. In contrast, the replacement of residues 357 through 397 of AcrA still produced a functional protein. We conclude that a small region of AcrA close to, but not at, its C terminus is involved in the interaction with its cognate pump protein, AcrB.

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