UCSF

Purpose: The purpose of this investigation was to study the effect of application of low electric current in combination with dilute chlorine dioxide in removal of planktonic bacterial counts and bacterial biofilm from a simulated dental unit waterline (DUWL). Our hypothesis was that bioelectric effect would greatly enhance the efficacy of antimicrobials in removal of bacteria from DUWL. This study was to assess the effect on biofilms of naturally occurring multiple species from actual DUWL.

Materials and Methods: A model DUWL was set-up to simulate a dental unit. Test and control tubings were connected to a peristaltic pump and then to a 10L reservoir. A current was applied along the length of the test DUWL. The 10L carboy was filled with softwater (Arrowhead) and DUWL microorganisms recovered from the planktonic 3-way air-water syringe (AWS) flow of 5 contaminated DUWLs were inoculated to create a biofilm on the inner wall of the tubings. Every Monday and Thursday, samples were collected from the effluent at the ends of the test and control waterlines and plated. One sample from each waterline was collected and plated in triplicates. Low current (10 mA) was applied to the test tubing in both experiments. During the second experiment dilute chlorine dioxide was added to the water. At the end of each experiment, the waterlines were disassembled and tubing sections were assessed for counts of viable bacteria.

Results: In experiment 1 we compared the effect of electric current to no current. After current was applied to the test tubing, the only time the counts from the effluent of the test sample (2.8x105 CFU/ml) were significantly different (lower) than the control sample (4.1x105 CFU/ml) was at day 38. Samples of biofilm bacteria after 28 days of current were collected from the barb-end and mid-section of the test and control tubing. The bacterial counts from the barb-end of the test tubing (9.9x103±2.2x103 CFU/cm²) were significantly lower (P=0.009) than those from the barb-end of the control tubing (3.2x104±7.9x103 CFU/cm2. The bacterial counts from the mid-section of the test tubing (3.0x104±2.6x103 CFU/cm²) were also statistically lower (P=0.004) than the bacterial counts from the mid-section of the control tubing (1.8x105±4.4x104 CFU/cm2). In experiment 2 we compared the effect of current in the presence of ClO2 to current alone. Effluent samples collected from the test tubing fluctuated from 101 to 103 CFU/ml. Effluent samples from the control tubing fluctuated from 10² to 104 CFU/ml. The differences were statistically significant at days 32, 40, 53, and 56. Samples of biofilm bacteria after 28 days of current were collected from the barb-end and mid-section of the test and control tubings. The bacterial counts from the barb-end of the test tubing (0) were significantly less (P=0.004) than those at the barb-end of the control tubing (1.0x104±3.1x103 CFU/cm2). Similarly, the bacterial counts from the mid-section of the test tubing (0) were significantly less (P=0.003) than those from the mid-section of the control tubing (8.8x103±2.2x103 CFU/cm2)

Conclusion: The combination of dilute chlorine dioxide and low current was effective in eradicating bacterial biofilm from a simulated DUWL. Current alone was not effective in eradicating bacterial biofilm from a simulated DUWL.