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Kavanaugh LG, Dey D, Shafer WM, Conn GL. Structural and functional diversity of Resistance-Nodulation-Division (RND) efflux pump transporters with implications for antimicrobial resistance. Microbiol Mol Biol Rev 2024:e0008923. [PMID: 39235227 DOI: 10.1128/mmbr.00089-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/06/2024] Open
Abstract
SUMMARYThe discovery of bacterial efflux pumps significantly advanced our understanding of how bacteria can resist cytotoxic compounds that they encounter. Within the structurally and functionally distinct families of efflux pumps, those of the Resistance-Nodulation-Division (RND) superfamily are noteworthy for their ability to reduce the intracellular concentration of structurally diverse antimicrobials. RND systems are possessed by many Gram-negative bacteria, including those causing serious human disease, and frequently contribute to resistance to multiple antibiotics. Herein, we review the current literature on the structure-function relationships of representative transporter proteins of tripartite RND efflux pumps of clinically important pathogens. We emphasize their contribution to bacterial resistance to clinically used antibiotics, host defense antimicrobials and other biocides, as well as highlighting structural similarities and differences among efflux transporters that help bacteria survive in the face of antimicrobials. Furthermore, we discuss technical advances that have facilitated and advanced efflux pump research and suggest future areas of investigation that will advance antimicrobial development efforts.
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Affiliation(s)
- Logan G Kavanaugh
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, USA
- Graduate Program in Microbiology and Molecular Genetics, Emory University, Atlanta, Georgia, USA
| | - Debayan Dey
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, USA
| | - William M Shafer
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA
- Laboratories of Microbial Pathogenesis, VA Medical Research Service, Veterans Affairs Medical Center, Decatur, Georgia, USA
- Emory Antibiotic Resistance Center, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Graeme L Conn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia, USA
- Emory Antibiotic Resistance Center, Emory University School of Medicine, Atlanta, Georgia, USA
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Schuster S, Vavra M, Wirth DAN, Kern WV. Comparative reassessment of AcrB efflux inhibitors reveals differential impact of specific pump mutations on the activity of potent compounds. Microbiol Spectr 2024; 12:e0304523. [PMID: 38170977 PMCID: PMC10846202 DOI: 10.1128/spectrum.03045-23] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 11/17/2023] [Indexed: 01/05/2024] Open
Abstract
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 Escherichia coli, and homologs in other Gram-negative bacteria. However, due to the often varying methodologies used for their characterization, results remain difficult to compare. In this study, using a defined selection of antibiotics known to be efflux substrates, we reevaluated 38 published compounds for their in vitro EPI activity. When examined in an E. coli strain with stable wild-type AcrB overexpression, we found 17 compounds showing at least fourfold enhancing potency with more than 2 out of 10 test drugs (belonging to eight antibiotic classes). Pyranopyridines (MBX series) were confirmed as the most potent inhibitors among agents reported so far. A new and surprising finding was that their activity, unlike that of the pyridylpiperazine EPI BDM88855, was highly susceptible to the AcrB double-mutation G141D_N282Y, which had previously been shown to diminish drug enhancing of 1-(1-naphthylmethyl)piperazine in a predominantly substrate-specific manner. Conversely, transmembrane region mutation V411A, while eliminating the drug potentiating of the BDM compound, did not decrease the activity of the MBX EPIs. Besides comparative reassessment of the potency of reported EPIs, the study demonstrated the usefulness of mutagenesis approaches providing tools for an initial discrimination of EPIs regarding their mode of function.IMPORTANCEInfections with difficult-to-treat multidrug-resistant bacteria pose an urgent global threat in view of the stagnating development of new antimicrobial substances. Efflux pumps in Gram-negative pathogens are known to substantially contribute to multidrug resistance making them promising targets for chemotherapeutic interventions to restore the efficacy of conventional antibiotics. In the present study, the in vitro activity of previously reported efflux pump inhibitors was reassessed using standardized conditions. Relevant drug sensitizing activity could be proven for almost half of the tested compounds. Further characterization of potent inhibitors was achieved by investigating the impact of specific efflux pump mutations. A double-mutation previously known to decrease the activity of the arylpiperazine 1-(1-naphthylmethyl)piperazine also impaired that of the highly efficient pyranopyridine efflux pump inhibitors. Our findings provide direct comparability of reported efflux pump inhibitors and contribute to the elucidation of their mode of action.
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Affiliation(s)
- Sabine Schuster
- Division of Infectious Diseases, Department of Medicine II, University Hospital and Medical Center, Freiburg, Germany
| | - Martina Vavra
- Division of Infectious Diseases, Department of Medicine II, University Hospital and Medical Center, Freiburg, Germany
| | - Dave A. N. Wirth
- Division of Infectious Diseases, Department of Medicine II, University Hospital and Medical Center, Freiburg, Germany
| | - Winfried V. Kern
- Division of Infectious Diseases, Department of Medicine II, University Hospital and Medical Center, Freiburg, Germany
- Faculty of Medicine, Albert-Ludwigs University, Freiburg, Germany
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Ge B, Mukherjee S, Li C, Harrison LB, Hsu CH, Tran TT, Whichard JM, Dessai U, Singh R, Gilbert JM, Strain EA, McDermott PF, Zhao S. Genomic analysis of azithromycin-resistant Salmonella from food animals at slaughter and processing, and retail meats, 2011-2021, United States. Microbiol Spectr 2024; 12:e0348523. [PMID: 37991374 PMCID: PMC10783062 DOI: 10.1128/spectrum.03485-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 10/18/2023] [Indexed: 11/23/2023] Open
Abstract
IMPORTANCE Macrolides of different ring sizes are critically important antimicrobials for human medicine and veterinary medicine, though the widely used 15-membered ring azithromycin in humans is not approved for use in veterinary medicine. We document here the emergence of azithromycin-resistant Salmonella among the NARMS culture collections between 2011 and 2021 in food animals and retail meats, some with co-resistance to ceftriaxone or decreased susceptibility to ciprofloxacin. We also provide insights into the underlying genetic mechanisms and genomic contexts, including the first report of a novel combination of azithromycin resistance determinants and the characterization of multidrug-resistant plasmids. Further, we highlight the emergence of a multidrug-resistant Salmonella Newport clone in food animals (mainly cattle) with both azithromycin resistance and decreased susceptibility to ciprofloxacin. These findings contribute to a better understating of azithromycin resistance mechanisms in Salmonella and warrant further investigations on the drivers behind the emergence of resistant clones.
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Affiliation(s)
- Beilei Ge
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Sampa Mukherjee
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Cong Li
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Lucas B. Harrison
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Chih-Hao Hsu
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Thu-Thuy Tran
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Jean M. Whichard
- Division of Foodborne, Waterborne, and Environmental Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Uday Dessai
- Food Safety and Inspection Service, U.S. Department of Agriculture, Washington, DC, USA
| | - Ruby Singh
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Rockville, Maryland, USA
| | - Jeffrey M. Gilbert
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Rockville, Maryland, USA
| | - Errol A. Strain
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Patrick F. McDermott
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
| | - Shaohua Zhao
- Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA
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Trampari E, Prischi F, Vargiu AV, Abi-Assaf J, Bavro VN, Webber MA. Functionally distinct mutations within AcrB underpin antibiotic resistance in different lifestyles. NPJ ANTIMICROBIALS AND RESISTANCE 2023; 1:2. [PMID: 38686215 PMCID: PMC11057200 DOI: 10.1038/s44259-023-00001-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 02/27/2023] [Indexed: 05/02/2024]
Abstract
Antibiotic resistance is a pressing healthcare challenge and is mediated by various mechanisms, including the active export of drugs via multidrug efflux systems, which prevent drug accumulation within the cell. Here, we studied how Salmonella evolved resistance to two key antibiotics, cefotaxime and azithromycin, when grown planktonically or as a biofilm. Resistance to both drugs emerged in both conditions and was associated with different substitutions within the efflux-associated transporter, AcrB. Azithromycin exposure selected for an R717L substitution, while cefotaxime for Q176K. Additional mutations in ramR or envZ accumulated concurrently with the R717L or Q176K substitutions respectively, resulting in clinical resistance to the selective antibiotics and cross-resistance to other drugs. Structural, genetic, and phenotypic analysis showed the two AcrB substitutions confer their benefits in profoundly different ways. R717L reduces steric barriers associated with transit through the substrate channel 2 of AcrB. Q176K increases binding energy for cefotaxime, improving recognition in the distal binding pocket, resulting in increased efflux efficiency. Finally, we show the R717 substitution is present in isolates recovered around the world.
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Affiliation(s)
- Eleftheria Trampari
- Quadram Institute Bioscience, Norwich Research Park, Norwich, Norfolk NR4 7UQ UK
| | - Filippo Prischi
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ UK
| | - Attilio V. Vargiu
- Department of Physics, University of Cagliari, S. P. 8, km. 0.700, 09042 Monserrato, Italy
| | - Justin Abi-Assaf
- Quadram Institute Bioscience, Norwich Research Park, Norwich, Norfolk NR4 7UQ UK
| | - Vassiliy N. Bavro
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ UK
| | - Mark A. Webber
- Quadram Institute Bioscience, Norwich Research Park, Norwich, Norfolk NR4 7UQ UK
- Medical School, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7UA UK
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