Abstract:
The Cedar River is the major coure of drinking water for the city of Seattle. However, the level of fecal colifoRMS in the raw water supply has exceeded limits set by Washington State in recent years, and as a result, the water utility may be required to install an extensive and costly filtration system. Tracing the fecal colifoRMS to their specific animal and/or human sources provides the information needed to interpret the significance of the fecal coliform levels, and to initiate appropriate control measures to assure a high quality water source.
Ribosomal RNA typing (ribotyping) was used to race the sources of fecal colifoRMS in the watershed. A collection of Escherichia coli strains were established from several locations in the Cedar River, from ten of the major animal species residing in the watershed, and from human rectal swabs and septic tanks near the watershed. Chromosomal DNA was isolated from each of the E. coli isolates, followed by restriction endonuclease digestion and Southern blotting. The blots were then hybridized with radiolabeled rRNA probe, and the banding patterns of the fragments were visualized by autoradiography. The ribotypes of the E. coli isolates from the contaminated site were then compared to the ribotypes of E. coli isolates from the possible sources of contamination.
The results show that the fecal pollution is of animal origin. Several different animal species had matches with water isolates, with canines as the most predominant. One human match was found but this same strain also matched a deer mouse. Since deer mice live in the watershed directly next to the river and the humans sampled live in Seattle, it is much mroe likely that the mouse was the source of the strain. Although the data indicates that human fecal pollution is not present, the animal wastes may contain protozoan pathogens Giardia and Cryptospiridium. A more comprehensive study is needed to perform a detailed identification of the sources of fecal foliforms, such that control measures to assure a high quality sourcec water can be established.