Comparative reassessment of AcrB efflux inhibitors reveals differential impact of specific pump mutations on the activity of potent compounds.

Multidrug resistance poses global challenges, particularly with regard to Gram-negative bacterial infections. In view of the lack of new antibiotics, drug enhancers, such as efflux pump inhibitors (EPIs), have increasingly come into focus. A number of chemically diverse agents have been reported to inhibit AcrB, the main multidrug transporter in , and homologs in other Gram-negative bacteria.

A Screening of Antimalarials Extends the Range of Known AcrB Efflux Substrates and Reveals Two Candidates with Antimicrobial Drug-Enhancing Activity.

Efflux by resistance nodulation cell division transporters, such as AcrAB-TolC in , substantially contributes to the development of Gram-negative multidrug resistance. Therefore, the finding of compounds that counteract efflux is an urgent goal in the fight against infectious diseases. Previously, an efflux inhibitory activity of the antimalarials mefloquine and artesunate was reported.

Exploring the Contribution of the AcrB Homolog MdtF to Drug Resistance and Dye Efflux in a Multidrug Resistant Isolate.

In , the role of RND-type drug transporters other than the major efflux pump AcrB has largely remained undeciphered (particularly in multidrug resistant pathogens), because genetic engineering in such isolates is challenging. The present study aimed to explore the capability of the AcrB homolog MdtF to contribute to the extrusion of noxious compounds and to multidrug resistance in an clinical isolate with demonstrated expression of this efflux pump. An / double-knockout was engineered, and susceptibility changes with drugs from various classes were determined in comparison to the parental strain and its and single-knockout mutants.

Limited Multidrug Resistance Efflux Pump Overexpression among Multidrug-Resistant Escherichia coli Strains of ST131.

Gram-negative bacteria partly rely on efflux pumps to facilitate growth under stressful conditions and to increase resistance to a wide variety of commonly used drugs. In recent years, sequence type 131 (ST131) has emerged as a major cause of extraintestinal infection frequently exhibiting a multidrug resistance (MDR) phenotype. The contribution of efflux to MDR in emerging MDR clones, however, is not well studied.

New Topoisomerase Inhibitors: Evaluating the Potency of Gepotidacin and Zoliflodacin in Fluoroquinolone-Resistant Escherichia coli upon Inactivation and Differentiating Their Efflux Pump Substrate Nature.

Inactivating in multidrug-resistant with differing sequence types and quinolone resistance-determining mutations reveals remarkably potentiated activity of the first-in-class topoisomerase inhibitors gepotidacin and zoliflodacin. Differences between both structurally unrelated compounds in comparison to fluoroquinolones regarding the selectivity of RND (resistance-nodulation-cell division)-type transporters, efflux inhibitors, and AcrB porter domain mutations were demonstrated. The findings should reinforce efforts to develop efflux-bypassing drugs and provide AcrB targets with critical relevance for this purpose.

Detection of High-Level Rifaximin Resistance in Enteric Bacteria by Agar Screen.

This study aimed at determining the prevalence of rifaximin resistance in a large collection of resistant to third-generation cephalosporins. A simple agar screen was developed to detect high-level resistance. A total of 401 isolates nonsusceptible to third-generation cephalosporins (including 342 and 39 spp.

Efflux-Mediated Resistance to New Oxazolidinones and Pleuromutilin Derivatives in Escherichia coli with Class Specificities in the Resistance-Nodulation-Cell Division-Type Drug Transport Pathways.

A major contribution of the resistance-nodulation-cell division (RND)-transporter AcrB to resistance to oxazolidinones and pleuromutilin derivatives in was confirmed. However, we discovered significant differences in efflux inhibitor activities, specificities of the homologous pump YhiV (MdtF), and the impact of AcrB pathway mutations. Particularly, entrance channel double-mutation I38F I671T and distal binding pocket mutation F615A revealed class-specific transport routes of oxazolidinones and pleuromutilin derivatives.

Proof of an Outer Membrane Target of the Efflux Inhibitor Phe-Arg-β-Naphthylamide from Random Mutagenesis.

Phe-Arg-β-naphthylamide (PAβN) has been characterized as an efflux pump inhibitor (EPI) acting on the major multidrug resistance efflux transporters of Gram-negative bacteria, such as AcrB in . In the present study, in vitro random mutagenesis was used to evolve resistance to the sensitizing activity of PAβN with the aim of elucidating its mechanism of action. A strain was obtained that was phenotypically similar to a previously reported mutant from a serial selection approach that had no efflux-associated mutations.

Mycobacteria exploit nitric oxide-induced transformation of macrophages into permissive giant cells.

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Contribution of AcrAB-TolC to multidrug resistance in an Escherichia coli sequence type 131 isolate.

Drug efflux by resistance-nodulation-cell division (RND)-type transporters, such as AcrAB-TolC of Escherichia coli, is an important resistance mechanism in Gram-negative bacteria; however, its contribution to multidrug resistance (MDR) in clinical isolates is poorly defined. We inactivated acrB of a sequence type 131 E. coli human isolate that showed high-level MDR, but had no mutations within the known efflux-associated local or global regulators.

Evidence of a Substrate-Discriminating Entrance Channel in the Lower Porter Domain of the Multidrug Resistance Efflux Pump AcrB.

Efflux pumps of the resistance nodulation cell division (RND) transporter family, such as AcrB of Escherichia coli, play an important role in the development of multidrug resistance, but the molecular basis for their substrate promiscuity is not yet completely understood. From a collection of highly clarithromycin-resistant AcrB periplasmic domain mutants derived from in vitro random mutagenesis, we identified variants with an unusually altered drug resistance pattern characterized by increased susceptibility to many drugs of lower molecular weight, including fluoroquinolones, tetracyclines, and oxazolidinones, but unchanged or increased resistance to drugs of higher molecular weight, including macrolides. Sequencing of 14 such "divergent resistance" phenotype mutants and 15 control mutants showed that this unusual phenotype was associated with mutations at residues I38 and I671 predominantly to phenylalanine and threonine, respectively, both conferring a similar susceptibility pattern.

Thioridazine and chlorpromazine inhibition of ethidium bromide efflux in Mycobacterium avium and Mycobacterium smegmatis.

Objectives: Therapy of AIDS patients infected with Mycobacterium avium is problematic due to its intrinsic resistance to antibiotics. We have characterized the efflux pump activity of M. avium wild-type strain through an automated fluorometric method and correlated it with intrinsic resistance to antibiotics.