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.