Biofilm removal from silicone tubing: an assessment of the efficacy of dialysis machine decontamination procedures using an in vitro model

The aim of this study was to assess the efficacy of 21 decontamination procedures, for the removal of a multispecies biofilm. Experiments were performed on five-day-old biofilms grown inside silicone tubing, using a reactor system that mimics a dialysis machine. The treatments were tested on 5 cm tubing samples. Effects of treatment were measured using direct microscopy following staining. Bacterial viability and endotoxin removal were determined using conventional microbiological methods following biofilm detachment by scraping. The 21 procedures were classified into four groups based on the amount of biofilm removed. The most effective treatment was an acid pre-treatment, followed by use of a concentrated bleach solution. Acid pre-treatment removes calcium and magnesium carbonate crystals that are always found in dialysis biofilms. Treatments performed at high temperature did not increase the efficacy of biofilm removal. Most treatments caused at least a 10(5)-fold reduction in bacterial viability with a few resulting in complete kill. Autoclaved and bleach-treated samples gave the best results for viability reduction, with both treatments providing an equally effective and complete kill. In addition, autoclaving led to a significant decrease in endotoxin level (removal of 99.99%).