Risk assessment of particle-associated bacteria in Melbourne's water supply

The level of turbidity in drinking water affects both its suitability for consumption and its aesthetic properties. Although a moderate level of turbidity does not itself provide a direct health risk, it has been reported that bacteria associated with these particles can exhibit an increased resistance to disinfection. The current study investigated the relationship between hydrophobicity and level of attachment, as well as how particle-association affects disinfection efficacy. Data was obtained from the physico-chemical characterisation of particles and bacteria (laboratory strains and environmental isolates), and from microbiological assays. Attachment was facilitated under nutrient deprivation and in the presence of an adsorbed organic substance, two conditions reported to influence adhesion. The concentration of chlorine required to neutralise a number of particle-associated samples was also determined. This allowed the preliminary assessment of relationships between adhesion and disinfection efficacy in anticipation of further work, and is part of an ongoing, quantitative evaluation of particle-mediated resistance within the water storage system of Melbourne, Australia.