Developing an ecologically relevant heterogeneous biofilm model for dental-unit waterlines

Abstract

This study monitored the biodiversity of microbes cultured from a heterogeneous biofilm which had formed on the lumen of a section of dental waterline tubing over a period of 910 days. By day 2 bacterial counts on the outlet-water showed that contamination of the system had occurred. After 14 days, a biofilm comparable to that of clinical waterlines, consisting of bacteria, fungi and amoebae had formed. This showed that the proprietary silver coating applied to the luminal surface of the commercial waterline tubing failed to prevent biofilm formation. Molecular barcoding of isolated culturable microorganisms showed some degree of the diversity of taxa in the biofilm, including the opportunistic pathogen Legionella pneumophila. Whilst the system used for isolation and identification of contaminating microorganisms may underestimate the diversity of organisms in the biofilm, their similarity to those found in the clinical environment makes this a promising test-bed for future biocide testing.

Keywords:

• Biofilm
• simulated waterline system
• Legionella pneumophila

Acknowledgements

The lead author (SL) would like to thank the Shah Abdul Latif University (Pakistan) and HEC-Pakistan, for the award of an overseas scholarship to study at the University of Central Lancashire, UK. The authors also express their gratitude to Mr Matthew McPhillips for discussions on Figure 1 and Mr David McCarthy for examination of the specimen grids and capturing images on behalf of Sham Lal as the privileged recipient of the 2013, Don Claugher Bursary. The prize was awarded by the Committee of the Society of Electron Microscope Technology (www.semt.org.uk).