title: A single nucleotide change in mutY increases the emergence of antibiotic-resistant Campylobacter jejuni mutants.
abstract: OBJECTIVE
  Mutator strains play an important role in the emergence of antibiotic-resistant bacteria. Campylobacter jejuni is a leading cause of foodborne illnesses worldwide and is increasingly resistant to clinically important antibiotics. The objective of this study was to identify the genetic basis that contributes to a mutator phenotype in Campylobacter and determine the role of this phenotype in the development of antibiotic resistance.
  
  
  METHODS
  A C. jejuni isolate (named CMT) showing a mutator phenotype was subjected to WGS analysis. Comparative genomics, site-specific reversion and mutation, and gene knockout were conducted to prove the mutator effect was caused by a single nucleotide change in the mutY gene of C. jejuni.
  
  
  RESULTS
  The C. jejuni CMT isolate showed ∼ 100-fold higher mutation frequency to ciprofloxacin than the WT strain. Under selection by ciprofloxacin, fluoroquinolone-resistant mutants emerged readily from the CMT isolate. WGS identified a single nucleotide change (G595 → T) in the mutY gene of the CMT isolate. Further experiments using defined mutant constructs proved its specific role in elevating mutation frequencies. The mutY point mutation also led to an ∼ 700-fold increase in the emergence of ampicillin-resistant mutants, indicating its broader impact on antibiotic resistance. Structural modelling suggested the G595 → T mutation probably affects the catalytic domain of MutY and consequently abolishes the anti-mutator function of this DNA repair protein.
  
  
  CONCLUSIONS
  The G595 → T mutation in mutY abolishes its anti-mutator function and confers a mutator phenotype in Campylobacter, promoting the emergence of antibiotic-resistant Campylobacter.
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Dai
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA.
authors.forename: Wayne T
authors.initials: WT
authors.lastname: Muraoka
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA.
authors.forename: Zuowei
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA.
authors.forename: Orhan
authors.initials: O
authors.lastname: Sahin
authors.affiliation: Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA zhang123@iastate.edu.
authors.forename: Qijing
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D002169:Campylobacter Infections / Q000382:microbiology*; D016123:Campylobacter jejuni / Q000187:drug effects* / Q000235:genetics*; D020134:Catalytic Domain / Q000235:genetics; D002939:Ciprofloxacin / Q000494:pharmacology; D045647:DNA Glycosylases / Q000737:chemistry / Q000235:genetics*; D024881:Drug Resistance, Bacterial; D016680:Genome, Bacterial; D023281:Genomics; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D059645:Mutation Rate; D020641:Polymorphism, Single Nucleotide
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002939:Ciprofloxacin; D045647:DNA Glycosylases