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

Resumo

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%, and 0.5%) 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.