Bacterial composition Inside Dental Unit Waterlines. Bacterial composition of DUWL

Microbial contamination of Dental Unit Waterlines (DUWL) has been regularly described during last decades, and yet, their overall bacterial composition has poorly been documented. In this study, the bacterial communities in dental unit waters (DUW) were characterized using 454-pyrosequencing-based analysis of 16S rRNA genes. Water samples were collected from seven dental offices ; the tap water supplying units (Incoming Water; IW) and the water from the turbine (Output water; OW) after a stagnation period (OWS), and also immediately after the last patient of the sampling day (OWA) were collected. Regardless of the observed inter-unit variability, results showed that the water flow within the dental unit (DU) correlates with an increase of the total bacterial cell concentration and shifts in bacterial community composition and abundance at the genus level, mainly within the Gamma- and Alpha-Proteobacteria class. Despite huge variations between sample categories, some bacterial taxa were found within all samples, defining a core microbiota representing (78.3%, 56.2% and 76.3%) of the total sequences from IW, OWA and OWS respectively. Results showed that the stagnation or flush are critical to the further bacterial community composition. The presence of potential pathogenic genera was detected, including Pseudomonas and Legionella spp. Emerging and opportunistic pathogenic genera such as Mycobacterium, Propionibacterium and Stenotrophomonas were also highlighted. An increase of the relative sequence abundance of the corresponding species was observed in OW, except for Propionibacterium sp. which was prevalent in IW. For the first time, a quite exhaustive evaluation of bacterial communities present in DUW was performed considering impact of water’s route inside DU. The highlight of the bacterial ecology plasticity throughout DUWL which is certainly controlled by multifactorial mechanisms (water treatments, maintenance...), contributes to a better appreciation of the potential infectious risk associated to dental cares. These findings suggest the importance to better manage the microbial quality in DUW.