Retention of a model pathogen in a porous media biofilm

The inadvertent or the deliberate introduction of pathogens into drinking water can lead to public health consequences. Distribution system sampling strategies are needed to provide information on the identity, source and fate of the introduced pathogens. Porous media biofilm reactors conditioned with undefined drinking water biofilms were tested for their ability to immobilize Escherichia coli 0157:H7. Biofilms were established by applying continuous flow of biologically activated carbon treated water with natural microflora and supplemented nutrient solution (0.5 mg l(-1) C) for 2 or 3 weeks. Control reactors were clean and were not colonized with biofilm. All reactors were injected with slug doses of approximately 1 x 10(9) cfu E. coli O157:H7. On the basis of the plate count enumeration of the introduced pathogen, reactors pre-colonized for 2 or 3 weeks retained significantly more cells (0.75 and 9.37% of the introduced spike dose, respectively) compared with uncolonized control reactors (0.22%). Compared with cultivation, microscopic direct counts and quantitative PCR suggested significantly higher and lower numbers of pathogens, respectively. Plate counts were thus considered as the method of choice for pathogen enumeration in this study. In addition to providing general insights into interactions between pathogens and drinking water biofilms, the study concluded that engineered biofilm systems may be considered as a device to capture pathogens from the bulk flow for monitoring purposes.