The biofilm-controlling functions of rechargeable antimicrobial N-halamine dental unit waterline tubing

Abstract

Objective: A study was conducted to test the biofilm-controlling functions of N-halamine tubing over an eight-month period.

Methods: A laboratory system, simulating a teaching dental clinic, was used to test rechargeable N-halamine tubing (T) compared to an untreated control (C) using the unit manufacturer's tubing. For the long-term study, a recharged tubing (RC) treated with bleach was used to compare with the test (T) and the control (C) tubing. Source tap water was cycled through the lines at 1.4 mL/minute, five minutes on and 25 minutes off, eight hours/day, five days/week. Every three weeks, samples of effluent, recovered adherent bacteria from inside tubing surfaces, and SEM images were examined for bacterial and biofilm growth. After sampling, a recharging solution of chlorine bleach (1 : 10 dilution) was run through T and RC lines, left overnight, and rinsed out the next morning. One-way ANOVAs and Spearman correlations were performed to detect significant differences for T, RC, and C, and determine significance with time period and source water, respectively.

Results: Mean log CFU/mL for C effluent > T (p = 0.028), and C tubing > T (p = 0.035). Spearman correlations were significant between effluent and source water level for T (rho = 0.817), and T tubing (0.750); between RC tubing and source water level (rho = 0.836), and time (rho = 0.745); and between C and time (rho = 0.873). SEM imaging confirmed the presence of biofilm inside RC and C, but not inside T.

Conclusion: N-halamine tubing completely inhibited biofilm formation without negatively affecting the physical properties of the effluent water. Further research on N-halamine tubing using a pure water source is recommended, as T effluent bacterial levels reflected the source tap water quality and proliferation of planktonic bacteria with no biofilm activity.

Figure 1A

The laboratory model comprised of a computerized system (A) used to pump water from carboys containing source water (B), through test (T) and control (C) lines into collection flasks (D).

Figure 1B

The test (T) and control (C) lines consisted of 5 cm sections of tubing connected together with 2 cm sections of silicon tubing.

Figure 1C

The adapted model with a tee barb connector used for connecting an additional recharge control (RC) line.

Figure 2A

Effluent bacterial levels in T and C lines during the 8-week preliminary testing. Lines were treated with 1:10 NaOCl bleach after 4 weeks.

Figure 2B

Bacterial levels from inside surfaces of T and C lines during the 8-week preliminary testing. Lines were treated with 1:10 NaOCl bleach after 4 weeks.

Figure 3A

Bacterial proliferation on inside surfaces of control (C) tubing after 4 weeks of preliminary testing.

Figure 3B

No evidence of bacterial presence on inside surfaces of test (T) tubing after 4 weeks of preliminary testing.

Figure 4A

Effluent bacterial levels in test (T), recharge control (RC), and control (C) lines over a 33-week testing period. Overall, T was significantly less contaminated than C (p < 0.05).

Figure 4B

Effluent bacterial levels in test (T), recharge control (RC), and control (C) lines as they relate to source tap water levels.

Figure 5A

Adherent bacterial levels recovered in PBS from inside surfaces of T, RC, and C over a 33-week testing period. Overall, T was significantly less contaminated than C (p < 0.05).

Figure 5B

Adherent bacterial levels recovered in PBS from inside surfaces of T, RC, and C as they relate to source tap water levels.

Figure 6

SEM images taken throughout the 33-week study from control line (A–D), recharge control line (E–H), and test line (I–L). Control line showed dense biofilm formation as early as Week 9, also noted on recharge control line showing less dense biofilm formation. There is no evidence of bacterial adhesion or biofilm formation on the test N-halamine line, even after 30 weeks.