Retention and Release of Cryptosporidium parvum Oocysts by Experimental Biofilms Composed of Natural Stream Microbial Communities
Cryptosporidium is a group of waterborne protozoan parasites that cause significant gastrointestinal disease in humans. The potential exists for these parasites to accumulate in stream or pipe surface biofilms and to be subsequently released to contaminate the water supply. Natural microbial assemblages were collected from three streams for three seasons (fall, winter, and spring) and used to grow biofilms in laboratory microcosms. These biofilms were then exposed to Cryptosporidium parvum oocysts via continuous inflow to determine daily influx, efflux, and biofilm retention and sloughing. Daily oocyst counts showed that oocysts attached to the biofilm quickly (within hours) and released slowly (within days). In these experiments, at least 40% of the oocysts added to the system attached to the biofilm in the first 72 hours, and at least 20% of the oocysts remained attached to the biofilm beyond 72 hours after the oocyst supply was removed. Although variation across site and season exists, likely as a result of variable microbial communities, all biofilms captured at least 40% of the oocysts and retained some of those oocysts for at least five days. The biofilm attachment and detachment dynamics of C. parvum oocysts have important implications for public health and suggest that biofilm monitoring should be included in routine water supply monitoring.