Occurrence and diversity of both bacterial and fungal communities in dental unit waterlines (DUWL) subjected to disinfectants

Chemical disinfectants are widely advocated to reduce the microbial contamination in dental unit waterlines (DUWL). However, until now their efficacy has been poorly examined after long-term application. In this study, the microbial community from three 8-12 year-old DUWL treated with two disinfectants commonly used by European dentists was investigated during routine dental practice. Water was collected from the tap water supplying units to the output exposure point of the turbine handpiece following a stagnation period and dental care activity. For the first time in this context, both bacterial and fungal communities were investigated using both quantitative PCR and 454 pyrosequencing. Results showed that the unit itself is the principal source of microbial contamination and that water stagnation, DU maintenance practices and quality of water supplying DU were critical for the water quality. Despite disinfecting treatment associated to flushing process, the microbial contamination remained relevant in the studied output water. The occurrence of potentially pathogenic microorganisms in these treated DUWL demonstrated a potential infectious risk for both patients and dental staff. Nevertheless, a disinfectant shock before a prolonged stagnation period could limit the microbial proliferation inside DUWL. Necessity to proceed to regular water quality control of DUWL was highlighted.