title: Proportional distribution of the red complex and its individual pathogens after sample storage using the checkerboard DNA-DNA hybridization technique.
abstract: BACKGROUND
  Information on the impact of sample storage prior to analysis by DNA methods is limited.
  
  
  OBJECTIVE
  To investigate the effect of microbial sample storage on bacterial detection and proportional distribution of the red complex and its individual pathogens.
  
  
  METHODS
  Subgingival plaque samples were analysed by (1) immediate processing, (2) after storage at +4 degrees C for 6 weeks, (3) after storage at -20 degrees C for 6 months or (4) after storage at -20 degrees C for 12 months using the checkerboard DNA-DNA hybridization.
  
  
  RESULTS
  Proportional distribution of the red complex did not differ between the first three protocols. However, the total bacterial DNA for pathogens studied decreased significantly in protocols 3 and 4. Relative amounts of Tannerella forsythensis, Porphyromonas gingivalis and Treponema denticola remained stable in the second protocols and changed in an unpredictable way if stored for 6 or 12 months.
  
  
  CONCLUSIONS
  Results from samples stored for maximum 6 months at -20 degrees C with high proportional amounts of the red complex and T. denticola may be used as an indicator of persistence. All bacterial samples for DNA extraction should be processed following a standardized storage protocol (i.e. samples stored at +4 degrees C for maximum 6 weeks) in order to get comparable qualitative and quantitative results for total DNA, bacterial complexes and individual pathogens. Most representative results are yielded if processing and hybridization could be performed immediately after sampling.
authors.affiliation: Department of Periodontology and Fixed Prosthodontics, School of Dental Medicine, University of Bern, CH-3010 Bern, Switzerland.
authors.forename: Joannis
authors.initials: J
authors.lastname: Katsoulis
authors.forename: Niklaus P
authors.initials: NP
authors.lastname: Lang
authors.forename: G Rutger
authors.initials: GR
authors.lastname: Persson
mesh_terms: D000704:Analysis of Variance; D015342:DNA Probes; D004269:DNA, Bacterial / Q000032:analysis*; D003773:Dental Plaque / Q000235:genetics / Q000382:microbiology*; D006801:Humans; D016014:Linear Models; D016966:Porphyromonas gingivalis / Q000235:genetics; D011309:Preservation, Biological; D018709:Statistics, Nonparametric; D013997:Time Factors; D048373:Treponema denticola / Q000235:genetics
chemical_list: D015342:DNA Probes; D004269:DNA, Bacterial