The TCA cycle is not required for selection or survival of multidrug-resistant Salmonella

Vito Ricci, Nick Loman, Mark Pallen, Alasdair Ivens, Maria Fookes, Gemma C Langridge, John Wain, Laura J V Piddock

Research output: Contribution to journalArticlepeer-review

Abstract

Objectives The initial aim of this study was to use a systems biology approach to analyse a ciprofloxacin-selected multidrug-resistant (MDR) Salmonella enterica serotype Typhimurium, L664.
Methods The whole genome sequence and transcriptome of L664 were analysed. Site-directed mutagenesis to recreate each mutation was carried out, followed by phenotypic characterization and mutation frequency analysis. As a mutation in the TCA cycle was detected we tested the controversial hypothesis regarding the bacterial response to bactericidal antibiotics, put forward by Kohanski et al. (Cell 2007; 130: 797–810 and Mol Cell 2010; 37: 311–20), that exposure of bacteria to agents such as ciprofloxacin produces reactive oxygen species (ROS), which transiently increase the mutation rate giving rise to MDR bacteria.
Results L664 contained a mutation in ramR that conferred MDR. A mutation in tctA affected the TCA cycle and conferred the inability to grow on minimal agar. The virulence of L664 was not attenuated. Ciprofloxacin exposure produced ROS in L664 and SL1344 (tctA::aph), but it was reduced and occurred later. There were no significant differences in the rates of killing or mutations per generation to antibiotic resistance between the strains.
Conclusions Whilst we confirm production of ROS in response to ciprofloxacin, we have no data to support the hypothesis that this leads to selection of MDR strains. Our results indicate that the mutations in tctA and glgA were random as they did not pre-exist in the parental strain, and that the mutation in tctA did not provide a survival advantage or disadvantage in the presence of antibiotic.
Original languageEnglish
Pages (from-to)589-599
Number of pages11
JournalJournal of Antimicrobial Chemotherapy
Volume67
Issue number3
DOIs
Publication statusPublished - Mar 2012

Keywords

  • Humans
  • Drug Resistance, Multiple, Bacterial
  • Reactive Oxygen Species
  • Salmonella typhimurium
  • Selection, Genetic
  • Mutagenesis, Site-Directed
  • Anti-Bacterial Agents
  • Ciprofloxacin
  • Microbial Viability
  • Systems Biology
  • Mutation
  • Transcriptome
  • Citric Acid Cycle

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