Evaluation of the level of microbial contamination and prevalence of gram-negative non-fermentative rods in dental unit waterlines

ABSTRACT

Introduction: The cross infection control in dental office has received great attention from professionals and one of the critical points is the bacteriological control of water used in dental unit. Objective: To perform a microbiological evaluation of the water used in dental units, the identification of Gram-negative non-fermentative rods (GNNR) and their ability to adhere to polystyrene, and the antimicrobial activity of disinfectants on the identified strains. Material and methods: The heterotrophic bacteria count and GNNR identification were performed on water samples collected from 25 dental units (air/water syringe and reservoir). The GNNR were assessed on their capability to adhere to polystyrene and on their antimicrobial activity to the following disinfectants sodium hypochlorite (0.06%, 0.12%, 0.25%, and0.5%) and chlorhexidine (0.03%, 0.06%, and 0.12%). Results: 88% of the air/water syringe collected samples and 68% of the reservoir collected samples were out of the potability standards. The quantity of isolated bacteria from the reservoir was lower than from the air/water syringe in 88% of the dental units. Methylobacterium spp. was found in highest percentage (19.7%) during GNNR genus isolation. There was a weak adherence to polystyrene in 85.04% of the samples. Sodium hypochlorite at 0.25%, inactivated 100% of the GNNRs in 10 minutes, while the highest tested concentration of chlorhexidine (0.12%), inactivated 98.5% of the GNNRs. Conclusion: These results provide information on the contamination problem of dental unit waterlines (DUWL) and indicate a need for treatment of the water used in dental units. The disinfection of DUWL can be performed with sodium hypochlorite at 0.25% (half the concentration recommended in the literature). However, further studies are necessary regarding DUWL frequency disinfection.