Microbial Contamination of Dental Unit Water Systems in Cork

Forde A1, Tobin M2*, O’Reilly P1, Fitzgerald G1, O’Sullivan M2, O’Mullane D2, 
Burke F3. 
1Microbiology Department, UCC.  2Oral Health Research Centre, UCC.  3Restorative Dentistry, UCC.

Objectives: To measure the level and nature of microbial contamination of Dental Unit Water Systems (DUWS) in General Dental Practice in Cork.

Methods: The study was funded under the EU 5th Framework Programme Contract No. QLK4-CT-2000-00097.  30 surgeries, 15 Health Board and 15 private practices, participated in the study.  DUWS samples were recovered from three points: (i) 3-in-1 syringe distal outlet, designated the water-line (WL) sample;  (ii) air-rotor line, the aerated water (AW) sample and (iii) a section of the tubing supplying the 3-in-1 syringe for biofilm analysis.  Samples of water and biofilm were plated on a range of selective and non-selective agar media to determine the microbial load and to test for the presence of opportunistic or true pathogens. 

Results: Thirty water-line (WL), 30 aerated water (AW) and 23 water-line biofilm (BF) samples were assessed.  Averages of 4.8 x 103 cfu ml-1,5.4 x 103 cfu ml-1  and 1.5 x 104 cfu ml-1were recovered from WL, AW and BF samples, respectively.  The available evidence suggested the presence of isolates most likely belonging to families of soil and aquatic bacteria such as Pseudomonas, Flavibacterium, Moraxella, Aerobacter, Micrococcus and Staphylococcus.  Opportunistic or true pathogens such as Escherichia coli, Pseudomonas aeruginosa and Legionella pneumophila were not detected.  Mycobacterium (non-pathogenic species) was found in six surgeries.  Yeasts were detected in samples from three surgeries but these were not Candida albicans.  

Conclusion:  Microorganisms recovered from the DUWS were not identified as pathogenic or potentially so, yet the bacterial count from several samples exceeded the accepted EU standard (100 cfu ml-1) for potable water.