title: Temporal changes in pulsed-field gel electrophoresis banding in vancomycin-resistant Enterococcus faecium and implications for outbreak investigations.
abstract: BACKGROUND
  Patients are often screened with surveillance cultures to discern transmissions vs transformation of an isolate to vancomycin-resistant Enterococcus faecium. To determine the amount of time between which isolates could be considered genetically similar by pulsed-field gel electrophoresis, isolate change over time within single patients was studied.
  
  
  METHODS
  A minimum of 4 isolates per patient, separated by at least 2 months, were collected from previously frozen stores. Visual comparison of banding patterns was conducted, and percent relatedness was calculated.
  
  
  RESULTS
  Twenty-eight isolates from 6 patients were studied. No isolate differed by more than 3 bands before 150 days, and the average percent difference per band was 3.7%. The isolates diverged genetically as a linear function of number of bands over time (good model fit intrapatient r(2) = 0.42; poor model fit interpatient r(2) = 0.0062).
  
  
  CONCLUSIONS
  Trajectory of genetic variation appears to be isolate/patient specific; however, commonalities exist and tested isolates were relatively stable out to 150 days.
authors.affiliation: Department of Pharmacy Practice, Chicago College of Pharmacy at Midwestern University, Downers Grove, IL 60515, USA.
authors.forename: Milena
authors.initials: M
authors.lastname: McLaughlin
authors.forename: Michael
authors.initials: M
authors.lastname: Malczynski
authors.forename: Chao
authors.initials: C
authors.lastname: Qi
authors.forename: Jordan
authors.initials: J
authors.lastname: Radetski
authors.forename: Teresa
authors.initials: T
authors.lastname: Zembower
authors.forename: Marc H
authors.initials: MH
authors.lastname: Scheetz
mesh_terms: D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D016984:Enterococcus faecium / Q000145:classification* / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D014644:Genetic Variation; D042822:Genomic Instability; D005838:Genotype; D016908:Gram-Positive Bacterial Infections / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D017720:Molecular Epidemiology / Q000379:methods; D058889:Molecular Typing; D020713:Vancomycin Resistance