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. 2019 Jul 24;16(15):2648.
doi: 10.3390/ijerph16152648.

Evaluation of Microbiological and Free-Living Protozoa Contamination in Dental Unit Waterlines

Free PMC article

Evaluation of Microbiological and Free-Living Protozoa Contamination in Dental Unit Waterlines

Anna Maria Spagnolo et al. Int J Environ Res Public Health. .
Free PMC article


Studies conducted over the last 40 years have demonstrated that the water output from dental unit waterlines (DUWLs) is often contaminated with high densities of microorganisms. It has been monitored the microbiological quality of the water in 30 public dental facilities in northern Italy in order to assess the health risk for patients and dental staff. In each facility, samples of water both from taps and from DUWLs were analyzed in order to evaluate heterotrophic plate counts (HPCs) at 22 °C and 36 °C, and to detect coliform bacteria, Pseudomonas aeruginosa, Legionella pneumophila and amoebae. In 100% of the samples taken from the DUWLs, the concentration of HPCs was above the threshold as determined by the Ministère de la Santé et des Solidarités (2007). The concentration of P. aeruginosa was greater than the indicated threshold in 16.67% of the hand-pieces analyzed. A total of 78.33% of samples were contaminated by L. pneumophila, while in the samples taken from the DUWLs alone, this percentage rose to 86.67%. Amoebae were detected in 60% of the samples taken from hand-pieces; all belonging to the species V. vermiformis. This study documented the presence of various microorganisms, including Legionella spp., at considerably higher concentrations in water samples from DUWLs than in samples of tap water in the same facilities, confirming the role of the internal DUWLs in increasing microbial contamination, especially in the absence of proper management of waterborne health risks.

Keywords: contamination; dental waterlines; infection risk.

Conflict of interest statement

The authors declare no conflicts of interest.


Figure 1
Figure 1
Percentage distribution of samples above and below target values for HPCs at 22 °C (100 CFU/mL or less), HPCs at 36 °C (10 CFU/mL or less), and P. aeruginosa (<1 CFU/100 mL) in tap water and hand-piece water.
Figure 2
Figure 2
Vermamoeba vermiformis from hand-piece water samples (inverted microscope, 40× objective).

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    1. Fujita M., Mashima I., Nakazawa F. Monitoring the decontamination efficacy of the novel Poseidon-S disinfectant system in dental unit water lines. J. Microbiol. Immunol. Infect. 2015;50:270–276. doi: 10.1016/j.jmii.2015.05.006. - DOI - PubMed
    1. Kohn W.G., Harte J.A., Malvitz D.M., Collins A.S., Cleveland J.L., Eklund K.J., Centers for Disease Control and Prevention Guidelines for infection control in dental health care settings-2003. J. Am. Dent. Assoc. 2004;135:33–47. doi: 10.14219/jada.archive.2004.0019. - DOI - PubMed
    1. Cristina M.L., Spagnolo A.M., Sartini M., Dallera M., Ottria G., Perdelli F., Orlando P. Investigation of organizational and hygiene features in dentistry: A pilot study. J. Prev. Med. Hyg. 2009;50:175–180. - PubMed
    1. Costa D., Mercier A., Gravouil K., Lesobre J., Delafont V., Bousseau A., Verdon J., Imbert C. Pyrosequencing analysis of bacterial diversity in dental unit waterlines. Water Res. 2015;81:223–231. doi: 10.1016/j.watres.2015.05.065. - DOI - PubMed
    1. Walker J.T., Bradshaw D.J., Bennett A.M., Fulford M.R., Martin M.V., Marsh P.D. Microbial biofilm formation and contamination of dental-unit water systems in general dental practice. Appl. Environ. Microbiol. 2000;66:3363–3367. doi: 10.1128/AEM.66.8.3363-3367.2000. - DOI - PMC - PubMed