Multi-species biofilms defined from drinking water microorganisms provide increased protection against chlorine disinfection

Abstract

A model biofilm, formed of multiple species from environmental drinking water, including opportunistic pathogens, was created to explore the tolerance of multi-species biofilms to chlorine levels typical of water-distribution systems. All species, when grown planktonically, were killed by concentrations of chlorine within the World Health Organization guidelines (0.2–5.0 mg l⁻¹). Higher concentrations (1.6–40-fold) of chlorine were required to eradicate biofilm populations of these strains, ∼70% of biofilms tested were not eradicated by 5.0 mg l⁻¹ chlorine. Pathogenic bacteria within the model multi-species biofilms had an even more substantial increase in chlorine tolerance; on average ∼700–1100 mg l⁻¹ chlorine was required to eliminate pathogens from the biofilm, 50–300-fold higher than for biofilms comprising single species. Confocal laser scanning microscopy of biofilms showed distinct 3D structures and multiple cell morphologies and arrangements. Overall, this study showed a substantial increase in the chlorine tolerance of individual species with co-colonization in a multi-species biofilm that was far beyond that expected as a result of biofilm growth on its own.

Keywords:

• biofilms
• drinking water
• chlorine resistance
• community biofilms
• water microbiology

Acknowledgments

The authors would like to acknowledge the support of the Ontario Ministry of the Environment and the Canadian Institutes of Health Research in the funding of this research. Further funding from Discovery Grants to RJT and HC from the Natural Sciences and Engineering Research Council of Canada. The authors would also like to thank Rhonda Schop, Carol Stremick, and the Alberta Provincial Laboratory for Public Health for their assistance.