scholarly journals Emergence of Two AcrB Substitutions Conferring Multidrug Resistance to Salmonella spp.

2021 ◽  
Vol 65 (5) ◽  
Author(s):  
Ling Yang ◽  
Haiyang Shi ◽  
Lijuan Zhang ◽  
Xiaoling Lin ◽  
Yinan Wei ◽  
...  
Keyword(s):  
Efflux Pump ◽  
Acid Sites ◽  
Site Directed Mutagenesis ◽  
Fluorescence Labeling ◽  
Directed Mutagenesis ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
Salmonella Spp ◽  
Multiple Substrates ◽  
High Level

ABSTRACT AcrAB-TolC is a major tripartite multidrug efflux pump conferring resistance to a wide variety of compounds in Gram-negative pathogens. Many AcrB mutants have been constructed through site-directed mutagenesis to probe the mechanism of AcrB function in antibiotic resistance. However, much less is known about the actual drug resistance-related mutants that naturally occur in clinically isolated pathogens. Here, we report two novel AcrB substitutions, M78I and P319L, in clinically isolated Salmonella strains with high-level ciprofloxacin resistance. Plasmids expressing the detected acrB mutations were constructed and introduced into SL1344 ΔacrB. Antimicrobial susceptibility assays showed that AcrB M78I, AcrB P319L, and AcrB M78I/319L all conferred reduced susceptibilities to multiple substrates, including fluoroquinolones, erythromycin, tetracyclines, bile salts, and dyes. Site-directed mutagenesis and MIC results revealed that the increased hydrophobicity of M78I was one of the reasons the AcrB M78I mutant had lower susceptibility to fluoroquinolones. Fluorescence labeling experiments suggested that the AcrB M78I substitution enhanced the binding of substrates to certain amino acid sites in the efflux pathway (e.g., sites Q89, E673, and F617) and weakened the binding to other amino acids (e.g., S134 and N274). Structural modeling disclosed that the increased flexibility of Leu was favorable for the functional rotation of AcrB compared to the original Pro residue. AcrA 319L makes the functional rotation of AcrB more flexible; this enables substrate efflux more efficiently. In order to understand the mechanism of AcrAB-TolC drug efflux well, the interaction between AcrA and AcrB in the role of the substrate efflux of AcrAB-TolC should be further investigated.

scholarly journals Fluoroquinolone Efflux by the Plasmid-Mediated Multidrug Efflux Pump QacB Variant QacBIII in Staphylococcus aureus

2010 ◽  
Vol 54 (10) ◽  
pp. 4107-4111 ◽  
Author(s):  
Hidemasa Nakaminami ◽  
Norihisa Noguchi ◽  
Masanori Sasatsu
Keyword(s):  
Staphylococcus Aureus ◽  
Amino Acid ◽  
Efflux Pump ◽  
Amino Acid Sequences ◽  
The Other ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
Substrate Specificities

ABSTRACT Plasmids that carry the multidrug efflux genes qacA and qacB are widely distributed in methicillin-resistant Staphylococcus aureus (MRSA). Although the QacA and QacB proteins are similar to each other, their respective substrate specificities may differ. We investigated the variability and structure-function relationships of QacA and QacB in MRSA isolates. The amino acid sequences of 7 QacA and 25 QacB proteins showed that QacB was present in three variants, designated QacBII, QacBIII, and QacBIV, that were different from the prototypic QacB variant encoded by plasmid pSK23, which was named QacBI, while QacA was present in two variants. When cloned and expressed in S. aureus, the strain carrying qacBIII exhibited higher susceptibility to dyes and decreased susceptibility to norfloxacin and ciprofloxacin compared to strains carrying the other QacB variants. Site-directed mutagenesis experiments revealed that the residue at position 320 in QacB plays an important role in the resistance phenotypes to dyes and fluoroquinolones. Furthermore, the accumulation of norfloxacin and ciprofloxacin in the strain carrying qacBIII was significantly decreased. Our data demonstrate that the plasmid-mediated multidrug efflux pump QacB variant QacBIII confers the capability for fluoroquinolone efflux on S. aureus.

scholarly journals Site-Directed Mutagenesis Reveals Putative Substrate Binding Residues in the Escherichia coli RND Efflux Pump AcrB

2008 ◽  
Vol 190 (24) ◽  
pp. 8225-8229 ◽  
Author(s):  
Jürgen A. Bohnert ◽  
Sabine Schuster ◽  
Markus A. Seeger ◽  
Eva Fähnrich ◽  
Klaas M. Pos ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Point Mutation ◽  
Efflux Pump ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
Rnd Efflux Pump ◽  
Binding Residues

ABSTRACT The Escherichia coli multidrug efflux pump protein AcrB has recently been cocrystallized with various substrates, suggesting that there is a phenylalanine-rich binding site around F178 and F615. We found that F610A was the point mutation that had the most significant impact on substrate MICs, while other targeted mutations, including conversion of phenylalanines 136, 178, 615, 617, and 628 to alanine, had smaller and more variable effects.

scholarly journals Genetic Characterization of Highly Fluoroquinolone-Resistant Clinical Escherichia coli Strains from China: Role ofacrR Mutations

2001 ◽  
Vol 45 (5) ◽  
pp. 1515-1521 ◽  
Author(s):  
Hui Wang ◽  
Joann L. Dzink-Fox ◽  
Minjun Chen ◽  
Stuart B. Levy
Keyword(s):  
Escherichia Coli ◽  
Blot Analysis ◽  
Genetic Basis ◽  
Efflux Pump ◽  
Pcr Amplification ◽  
Fluoroquinolone Resistance ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
E Coli ◽  
High Level

ABSTRACT The genetic basis for fluoroquinolone resistance was examined in 30 high-level fluoroquinolone-resistant Escherichia coliclinical isolates from Beijing, China. Each strain also demonstrated resistance to a variety of other antibiotics. PCR sequence analysis of the quinolone resistance-determining region of the topoisomerase genes (gyrA/B, parC) revealed three to five mutations known to be associated with fluoroquinolone resistance. Western blot analysis failed to demonstrate overexpression of MarA, and Northern blot analysis did not detect overexpression of soxS RNA in any of the clinical strains. The AcrA protein of the AcrAB multidrug efflux pump was overexpressed in 19 of 30 strains of E. colitested, and all 19 strains were tolerant to organic solvents. PCR amplification of the complete acrR (regulator/repressor) gene of eight isolates revealed amino acid changes in four isolates, a 9-bp deletion in another, and a 22-bp duplication in a sixth strain. Complementation with a plasmid-borne wild-type acrR gene reduced the level of AcrA in the mutants and partially restored antibiotic susceptibility 1.5- to 6-fold. This study shows that mutations in acrR are an additional genetic basis for fluoroquinolone resistance.

scholarly journals Identification of a Novel Multidrug Efflux Pump of Mycobacterium tuberculosis

2008 ◽  
Vol 52 (7) ◽  
pp. 2503-2511 ◽  
Author(s):  
Olga Danilchanka ◽  
Claudia Mailaender ◽  
Michael Niederweis
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Outer Membrane ◽  
Bacterial Infections ◽  
Molecular Mechanisms ◽  
Efflux Pump ◽  
Model Organism ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
Efflux Pump Inhibitor ◽  
High Level

ABSTRACT The impermeability of the outer membrane in combination with drug efflux are major determinants of the natural drug resistance of mycobacteria. β-Lactams are the most widely used antibiotics for treatment of bacterial infections. However, it is unknown how β-lactams enter Mycobacterium tuberculosis and whether efflux pumps exist that can export these drugs out of the cell. To identify the molecular mechanisms of M. tuberculosis resistance to β-lactams, a library of 7,500 transposon mutants was generated in the model organism Mycobacterium bovis BCG. Thirty-three unique insertion sites were determined that conferred medium or high-level (≥2,000 μg/ml) resistance to ampicillin. Three mutants in sulfolipid synthesis or transport were highly resistant to ampicillin, indicating an indirect effect of the lipid composition on the outer membrane permeability of M. bovis BCG to ampicillin. Mutants with insertions in genes encoding surface molecules such as PPE proteins or lipoarabinomannan were also completely resistant to ampicillin, thus suggesting a lack of transport across the outer membrane. Insertion of the transposon in front of bcg0231 increased transcription of the gene and concomitantly the resistance of M. bovis BCG to ampicillin, streptomycin, and chloramphenicol by 32- to 64-fold. Resistance to vancomycin and tetracycline was increased four- to eightfold. Bcg0231 and Rv0194 are almost identical ATP-binding cassette transporters. Expression of rv0194 significantly reduced accumulation of ethidium bromide and conferred multidrug resistance to Mycobacterium smegmatis. Both effects were abrogated in the presence of the efflux pump inhibitor reserpine. These results demonstrate that Rv0194 is a novel multidrug efflux pump of M. tuberculosis.

scholarly journals Innate Aminoglycoside Resistance of Achromobacter xylosoxidans Is Due to AxyXY-OprZ, an RND-Type Multidrug Efflux Pump

2012 ◽  
Vol 57 (1) ◽  
pp. 603-605 ◽  
Author(s):  
Julien Bador ◽  
Lucie Amoureux ◽  
Emmanuel Blanc ◽  
Catherine Neuwirth
Keyword(s):  
Efflux Pump ◽  
Multidrug Resistant ◽  
Achromobacter Xylosoxidans ◽  
Pulmonary Infections ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
Aminoglycoside Resistance ◽  
Content Type ◽  
High Level ◽  
Level Resistance

ABSTRACTAchromobacter xylosoxidansis an innately multidrug-resistant pathogen which is emerging in cystic fibrosis (CF) patients. We characterized a new resistance-nodulation-cell division (RND)-type multidrug efflux pump, AxyXY-OprZ. This system is responsible for the intrinsic high-level resistance ofA. xylosoxidansto aminoglycosides (tobramycin, amikacin, and gentamicin). Furthermore, it can extrude cefepime, carbapenems, some fluoroquinolones, tetracyclines, and erythromycin. Some of the AxyXY-OprZ substrates are major components widely used to treat pulmonary infections in CF patients.

scholarly journals A Periplasmic Drug-Binding Site of the AcrB Multidrug Efflux Pump: a Crystallographic and Site-Directed Mutagenesis Study

2005 ◽  
Vol 187 (19) ◽  
pp. 6804-6815 ◽  
Author(s):  
Edward W. Yu ◽  
Julio R. Aires ◽  
Gerry McDermott ◽  
Hiroshi Nikaido
Keyword(s):  
Binding Site ◽  
Transmembrane Domain ◽  
Efflux Pump ◽  
Drug Binding ◽  
Site Directed Mutagenesis ◽  
Multidrug Efflux ◽  
Multidrug Efflux Pump ◽  
Central Cavity ◽  
Intact Cells ◽  
Drug Binding Site

ABSTRACT The Escherichia coli AcrB multidrug efflux pump is a membrane protein that recognizes many structurally dissimilar toxic compounds. We previously reported the X-ray structures of four AcrB-ligand complexes in which the ligands were bound to the wall of the extremely large central cavity in the transmembrane domain of the pump. Genetic studies, however, suggested that discrimination between the substrates occurs mainly in the periplasmic domain rather than the transmembrane domain of the pump. We here describe the crystal structures of the AcrB mutant in which Asn109 was replaced by Ala, with five structurally diverse ligands, ethidium, rhodamine 6G, ciprofloxacin, nafcillin, and Phe-Arg-β-naphthylamide. The ligands bind not only to the wall of central cavity but also to a new periplasmic site within the deep external depression formed by the C-terminal periplasmic loop. This depression also includes residues identified earlier as being important in the specificity. We show here that conversion into alanine of the Phe664, Phe666, or Glu673 residue in the periplasmic binding site produced significant decreases in the MIC of most agents in the N109A background. Furthermore, decreased MICs were also observed when these residues were mutated in the wild-type AcrB background, although the effects were more modest. The MIC data were also confirmed by assays of ethidium influx rates in intact cells, and our results suggest that the periplasmic binding site plays a role in the physiological process of drug efflux.

scholarly journals Molecular Insights into an Antibiotic Enhancer Action of New Morpholine-Containing 5-Arylideneimidazolones in the Fight against MDR Bacteria

2021 ◽  
Vol 22 (4) ◽  
pp. 2062
Author(s):  
Aneta Kaczor ◽  
Karolina Witek ◽  
Sabina Podlewska ◽  
Veronique Sinou ◽  
Joanna Czekajewska ◽  
...  
Keyword(s):  
Molecular Modelling ◽  
Efflux Pump ◽  
Gram Negative Bacteria ◽  
Potential Mechanism ◽  
Multidrug Efflux ◽  
Aromatic Rings ◽  
Allosteric Site ◽  
Multidrug Efflux Pump ◽  
Dual Action

In the search for an effective strategy to overcome antimicrobial resistance, a series of new morpholine-containing 5-arylideneimidazolones differing within either the amine moiety or at position five of imidazolones was explored as potential antibiotic adjuvants against Gram-positive and Gram-negative bacteria. Compounds (7–23) were tested for oxacillin adjuvant properties in the Methicillin-susceptible S. aureus (MSSA) strain ATCC 25923 and Methicillin-resistant S. aureus MRSA 19449. Compounds 14–16 were tested additionally in combination with various antibiotics. Molecular modelling was performed to assess potential mechanism of action. Microdilution and real-time efflux (RTE) assays were carried out in strains of K. aerogenes to determine the potential of compounds 7–23 to block the multidrug efflux pump AcrAB-TolC. Drug-like properties were determined experimentally. Two compounds (10, 15) containing non-condensed aromatic rings, significantly reduced oxacillin MICs in MRSA 19449, while 15 additionally enhanced the effectiveness of ampicillin. Results of molecular modelling confirmed the interaction with the allosteric site of PBP2a as a probable MDR-reversing mechanism. In RTE, the compounds inhibited AcrAB-TolC even to 90% (19). The 4-phenylbenzylidene derivative (15) demonstrated significant MDR-reversal “dual action” for β-lactam antibiotics in MRSA and inhibited AcrAB-TolC in K. aerogenes. 15 displayed also satisfied solubility and safety towards CYP3A4 in vitro.

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