title: Emergence of a Potent Multidrug Efflux Pump Variant That Enhances Campylobacter Resistance to Multiple Antibiotics.
abstract: Bacterial antibiotic efflux pumps are key players in antibiotic resistance. Although their role in conferring multidrug resistance is well documented, the emergence of "super" efflux pump variants that enhance bacterial resistance to multiple drugs has not been reported. Here, we describe the emergence of a resistance-enhancing variant (named RE-CmeABC) of the predominant efflux pump CmeABC in Campylobacter, a major zoonotic pathogen whose resistance to antibiotics is considered a serious antibiotic resistance threat in the United States. Compared to the previously characterized CmeABC transporters, RE-CmeABC is much more potent in conferring Campylobacter resistance to antibiotics, which was shown by increased MICs and reduced intracellular accumulation of antibiotics. Structural modeling suggests that sequence variations in the drug-binding pocket of CmeB possibly contribute to the enhanced efflux function. Additionally, RE-CmeABC expands the mutant selection window of ciprofloxacin, enhances the emergence of antibiotic-resistant mutants, and confers exceedingly high-level resistance to fluoroquinolones, an important class of antibiotics for clinical therapy of campylobacteriosis. Furthermore, RE-CmeABC is horizontally transferable, shifts antibiotic MIC distribution among clinical isolates, and is increasingly prevalent in Campylobacter jejuni isolates, suggesting that it confers a fitness advantage under antimicrobial selection. These findings reveal a new mechanism for enhanced multidrug resistance and an effective strategy utilized by bacteria for adaptation to selection from multiple antibiotics.
  
  
  
  Bacterial antibiotic efflux pumps are ubiquitously present in bacterial organisms and protect bacteria from the antibacterial effects of antimicrobials and other toxic compounds by extruding them out of cells. Thus, these efflux transporters represent an important mechanism for antibiotic resistance. In this study, we discovered the emergence and increasing prevalence of a unique efflux pump variant that is much more powerful in the efflux of antibiotics and confers multidrug resistance in Campylobacter, which is a major foodborne pathogen transmitted to humans via the food chain. Unlike other specific resistance determinants that only allow bacteria to resist a particular antimicrobial, the acquisition of a functionally enhanced efflux pump will empower bacteria with simultaneous resistance to multiple classes of antibiotics. These findings reveal a previously undescribed mechanism for enhanced multidrug resistance and open a new direction for us to understand how bacteria adapt to antibiotic treatment.
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Yao
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA.
authors.forename: Zhangqi
authors.initials: Z
authors.lastname: Shen
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA.
authors.forename: Fengru
authors.initials: F
authors.lastname: Deng
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
authors.forename: Dejun
authors.initials: D
authors.lastname: Liu
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
authors.forename: Gaowa
authors.initials: G
authors.lastname: Naren
authors.affiliation: College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Dai
authors.affiliation: Department of Physics and Astronomy, Iowa State University, Ames, Iowa, USA.
authors.forename: Chih-Chia
authors.initials: CC
authors.lastname: Su
authors.affiliation: Food Safety and Technology Department, University of Nebraska, Lincoln, Nebraska, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
authors.forename: Shaolin
authors.initials: S
authors.lastname: Wang
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
authors.forename: Congming
authors.initials: C
authors.lastname: Wu
authors.affiliation: Department of Physics and Astronomy, Iowa State University, Ames, Iowa, USA.
authors.forename: Edward W
authors.initials: EW
authors.lastname: Yu
authors.affiliation: College of Veterinary Medicine, Iowa State University, Ames, Iowa, USA sjz@cau.edu.cn zhang123@iastate.edu.
authors.forename: Qijing
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China sjz@cau.edu.cn zhang123@iastate.edu.
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Shen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D002167:Campylobacter / Q000187:drug effects* / Q000235:genetics*; D016123:Campylobacter jejuni / Q000187:drug effects; D024901:Drug Resistance, Multiple, Bacterial; D024841:Fluoroquinolones / Q000494:pharmacology; D006801:Humans; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins