title: Antibiotic pressure can induce the viable but non-culturable state in Staphylococcus aureus growing in biofilms.
abstract: OBJECTIVE
  Staphylococcal biofilms are among the main causes of chronic implant-associated infections. We have recently suggested that their transformation into viable but non-culturable (VBNC) forms (i.e. forms capable of resuscitation) could be responsible for the recurrent symptoms. This work aims to establish whether Staphylococcus aureus biofilms can give rise to VBNC forms capable of being resuscitated in suitable environmental conditions, the role of different stressors in inducing the VBNC state and the conditions favouring resuscitation.
  
  
  METHODS
  S. aureus 10850 biofilms were exposed to different concentrations of antibiotic (vancomycin or quinupristin/dalfopristin) and/or to nutrient depletion until loss of culturability. The presence of viable cells and their number were examined by epifluorescence microscopy and flow cytometry. Gene expression was measured by real-time PCR. Resuscitation ability was tested by growth in rich medium containing antioxidant factors.
  
  
  RESULTS
  Viable subpopulations were detected in all non-culturable biofilms. However, viable cell numbers and gene expression remained constant for 150 days from loss of culturability in cells from antibiotic-exposed biofilms, but not in those that had only been starved. Resuscitation was obtained in rich medium supplemented with 0.3% sodium pyruvate or with 50% filtrate of a late-log culture.
  
  
  CONCLUSIONS
  Our findings demonstrate that S. aureus can enter the VBNC state in infectious biofilms. The presence of vancomycin or quinupristin/dalfopristin can inadvertently induce a true VBNC state or its persistence in S. aureus cells embedded in biofilms, supporting previous findings on the role of staphylococcal biofilms in recurrent infections.
authors.affiliation: Department of Life and Environmental Sciences, Polytechnic University of Marche, Ancona, Italy. s.pasquaroli@univpm.it
authors.forename: S
authors.initials: S
authors.lastname: Pasquaroli
authors.forename: G
authors.initials: G
authors.lastname: Zandri
authors.forename: C
authors.initials: C
authors.lastname: Vignaroli
authors.forename: C
authors.initials: C
authors.lastname: Vuotto
authors.forename: G
authors.initials: G
authors.lastname: Donelli
authors.forename: F
authors.initials: F
authors.lastname: Biavasco
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D058491:Bacterial Load; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development*; D048749:Cytokinesis / Q000187:drug effects*; D020869:Gene Expression Profiling; D050296:Microbial Viability / Q000187:drug effects*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development*; D014640:Vancomycin / Q000494:pharmacology; D014769:Virginiamycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D014640:Vancomycin
keywords: quinupristin/dalfopristin; recurrent infections; vancomycin