Assessment of nosocomial bacterial contamination in dental unit waterlines: Impact of flushing

Purpose: This study evaluated the extent of bacterial contamination in water from dental unit waterlines (DUWLs). Methodology: Water samples were collected (before flushing, 1 min post-flushing, and 3 min post-flushing) from 24 clinics (Group A: no disinfection, Group B: citric acid disinfectant) of a Government Dental College. Bacterial counts, identification, antibiotic sensitivity tests, determination of endotoxin levels, and scanning electron microscopy (to confirm the presence of biofilm) were performed. Results: The most common opportunistic bacteria were P. aeruginosa (95%), S. aureus (58%), S. auricularis (49%), P. fluorescens (44%), and A. baumannii (20%). Approximately 50% of the bacterial isolates were resistant to two or more antibiotics. Flushing for 3 min did not reduce the contamination of water from Group A clinics which exceeded the recommendation of <= 500 CFU/ml. No bacterial growth was seen in Group B samples. Endotoxin levels were >5.00 endotoxin units (EU)/ml in Group A and ranged from 1.33 to 5.00 EU/ml in Group B clinics. Scanning electron microscopy images showed bacterial biofilms on the surfaces of the tubes. Conclusions: DUWL contamination is a serious issue in dentistry, and the microbiological quality of the water must be monitored regularly. Further studies on endotoxin exposure and prevention are therefore necessary. (C) 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.