title: Prevention of biofilm formation in dialysis water treatment systems.
abstract: BACKGROUND
  Biofilm formations in dialysis systems may be relevant because they continuously release bacterial compounds and are resistant against disinfection. The aim of the study was to compare the development of biofilm between a water treatment system based on a single reverse osmosis unit producing purified dialysate water [bacterial count, 350 colony-forming unit (CFU)/L] (center A) and a water treatment system based on double reverse osmosis and electric deionization, which is continuously disinfected with ultraviolet light and treated with ozone once a week (bacterial count, 1 CFU/L) (center B).
  
  
  METHODS
  During a period of 12 weeks, biofilm formation was studied in the tubing segment between the water piping and the dialysis module, using four dialysis monitors in each center. On a weekly basis, tubing samples of 5 cm length (N = 96) were taken under aseptic conditions and investigated for microbiologic contamination [cystine lactose electrolyte-deficient (CLED) Agar], endotoxin levels [limulus amoeben lysate (LAL) gel test, cutoff value, 0.0125 EU/mL], and biofilm formation [electron scanning microscopy (SEM)].
  
  
  RESULTS
  In center A, tube cultures were positive (>100 CFU/mL) in 16% of samples at 22 degrees C and 37 degrees C, compared to 3% of samples of center B (P < 0.05; chi-square). Endotoxin levels were positive in 76% of the tubing samples of center A and negative in all of the samples of center B (P < 0.05). Biofilm was present in 91.7% of the samples of center A (Fig. 1), and only present in one sample (taken after 9 weeks) of center B (P < 0.05) (Fig. 2). In center A, biofilm formation was already observed after 1 week.
  
  
  CONCLUSIONS
  In contrast to a standard water treatment system producing purified water, the use of a system producing highly purified water, which is also treated with regular disinfection procedures, leads to a significant reduction in biofilm formation, bacterial growth, and endotoxin levels in a highly vulnerable part of a water treatment system.
authors.affiliation: Department of Medical Microbiology, University Hospital Maastricht, University of Maastricht, Maastricht, The Netherlands.
authors.forename: Ed
authors.initials: E
authors.lastname: Smeets
authors.forename: Jeroen
authors.initials: J
authors.lastname: Kooman
authors.forename: Frank
authors.initials: F
authors.lastname: van der Sande
authors.forename: Ellen
authors.initials: E
authors.lastname: Stobberingh
authors.forename: Peter
authors.initials: P
authors.lastname: Frederik
authors.forename: Piet
authors.initials: P
authors.lastname: Claessens
authors.forename: Willem
authors.initials: W
authors.lastname: Grave
authors.forename: Arend
authors.initials: A
authors.lastname: Schot
authors.forename: Karel
authors.initials: K
authors.lastname: Leunissen
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D004203:Disinfection / Q000379:methods*; D008828:Microbiological Techniques; D009995:Osmosis; D006435:Renal Dialysis; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods*