title: Increased mutability of Staphylococci in biofilms as a consequence of oxidative stress.
abstract: OBJECTIVE
  To investigate the development of mutational resistance to antibiotics in staphylococcal biofilms.
  
  
  METHODS
  Mutation frequencies to resistance against mupirocin and rifampicin were determined for planktonic cultures and for biofilms generated using either a novel static biofilm model or by continuous flow. DNA microarray analysis was performed to detect differences in transcriptional profiles between planktonic and biofilm cultures.
  
  
  RESULTS
  The mutability of biofilm cultures increased up to 60-fold and 4-fold for S. aureus and S. epidermidis, respectively, compared with planktonic cultures. Incorporation of antioxidants into S. aureus biofilms reduced mutation frequencies, indicating that increased oxidative stress underlies the heightened mutability. Transcriptional profiling of early biofilm cultures revealed up-regulation of the superoxide dismutase gene, sodA, also suggestive of enhanced oxidative stress in these cultures. The addition of catalase to biofilms of S. aureus SH1000 reduced mutation frequencies, a finding which implicated hydrogen peroxide in increased biofilm mutability. However, catalase had no effect on biofilm mutability in S. aureus UAMS-1, suggesting that there is more than one mechanism by which the mutability of staphylococci may increase during the biofilm mode of growth.
  
  
  CONCLUSIONS
  Our findings suggest that biofilms represent an enriched source of mutational resistance to antibiotics in the staphylococci.
authors.affiliation: Antimicrobial Research Centre, Faculty of Biological Sciences, University of Leeds, United Kingdom.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Ryder
authors.forename: Ian
authors.initials: I
authors.lastname: Chopra
authors.forename: Alex J
authors.initials: AJ
authors.lastname: O'Neill
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D001426:Bacterial Proteins / Q000378:metabolism; D018441:Biofilms; D017931:DNA Primers / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000502:physiology*; D016712:Mupirocin; D059645:Mutation Rate; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012293:Rifampin; D013210:Staphylococcus / Q000235:genetics*; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D000975:Antioxidants; D001426:Bacterial Proteins; D017931:DNA Primers; D016712:Mupirocin; C095500:SodA protein, Bacteria; D013482:Superoxide Dismutase; D012293:Rifampin