title: Characterization of multi-drug tolerant persister cells in Streptococcus suis.
abstract: BACKGROUND
  Persister cells constitute a subpopulation of dormant cells within a microbial population which are genetically identical but phenotypically different to regular cells. Notably, persister cells show an elevated tolerance to antimicrobial agents. Thus, they are considered to represent a microbial 'bet-hedging' strategy and are of particular importance in pathogenic bacteria.
  
  
  RESULTS
  We studied the ability of the zoonotic pathogen Streptococcus (S.) suis to form multi-drug tolerant variants and identified persister cells dependent on the initial bacterial growth phase. We observed lower numbers of persisters in exponential phase cultures than in stationary growth phase populations. S. suis persister cells showed a high tolerance to a variety of antibiotics, and the phenotype was not inherited as tested with four passages of S. suis populations. Furthermore, we provide evidence that the persister phenotype is related to expression of genes involved in general metabolic pathways since we found higher numbers of persister cells in a mutant strain defective in the catabolic arginine deiminase system as compared to its parental wild type strain. Finally, we observed persister cell formation also in other S. suis strains and pathogenic streptococcal species.
  
  
  CONCLUSIONS
  Taken together, this is the first study that reports multi-drug tolerant persister cells in the zoonotic pathogen S. suis.
authors.affiliation: Institute of Microbiology, University of Veterinary Medicine, Hannover, Germany. joerg.willenborg@tiho-hannover.de.
authors.forename: Jörg
authors.initials: J
authors.lastname: Willenborg
authors.forename: Daniela
authors.initials: D
authors.lastname: Willms
authors.forename: Ralph
authors.initials: R
authors.lastname: Bertram
authors.forename: Ralph
authors.initials: R
authors.lastname: Goethe
authors.forename: Peter
authors.initials: P
authors.lastname: Valentin-Weigand
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004361:Drug Tolerance; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects*; D010641:Phenotype; D017011:Streptococcus suis / Q000187:drug effects* / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents