Benzalkonium Chloride Efficacy Against Biofilm-Producing Microorganisms in Dental Unit Waterlines

Objectives:
Purpose: The purpose of the study was to investigate the efficacy of 0.6% Benzalkonium Chloride (BZK) against biofilm-producing microorganisms such as K. pneumonia (KP), P. aeroginosa (PA), E. faecalis (EF), S. aureus (SA), E. coli (EC) and C. albicans (CA) on dental unit waterlines (DUWL) using the Minimum Inhibitory Concentration/Minimum Bactericidal Concentration (MIC/MBC) methods, Kirby Bauer Test, and Time-Kill assays.
Methods: Methods: Serially diluted (1:2 dilutions) the 0.6% BZK and equal volume of the organism (1x10⁶/mL) was added to each dilution including positive and negative controls. The MIC was determined after 24 hours of incubation. Clear tubes were plated to determine the MBC. The Kirby Bauer Test was conducted by placing filter paper disc soaked with BZK onto four quadrants of the plates including negative and positive controls. Time-Kill assay concentration was based on 4X MIC and the exposure time was set at 30 minutes and 24 hours. Samples were plated after the desired exposure time including the control without BZK to determine inoculum concentration.
Results: Results: The MIC results provided the following results: EC and PA (47 μg/mL), KP (24 μg/mL), CA (12 μg/mL), EF and SA (<6 μg/mL). For MBC, the results were as follows: CA and SA (24 μg/mL), EF (47 μg/mL), EC (94 μg/mL), KP (375 μg/mL and PA (750 μg/mL). Kirby Bauer Test showed Zone of Inhibition ranging from 8 mm (PA) to 30 mm (SA). The Time-Kill assay found no growth of EC, KP, PA after 30 minutes of exposure whereas CA, EF and SA showed a range of 1-4 log reduction. After 24-hours, none of the bacteria showed growth on agar plates.
Conclusions: Conclusion: Under the conditions of present study, 0.6% Benzalkonium Chloride has significant bacteriostatic and bactericidal effects against the selected biofilm-producing organisms.