CORVALLIS, Ore. - An Oregon State University microbiologist has developed a molecular test to determine the source of fecal contamination in water.
This type of detection, called "fecal source tracking," is both faster and far more specific than traditional standard fecal coliform tests, according to Katharine G. Field, who developed the test. Results of a Tillamook Bay-based study using the new methodology were published in a recent issue of Applied and Environmental Microbiology (http://aem.asm.org/cgi/content/abstract/72/8/5537)
Field and her colleagues found a way to use gene amplification to determine the kind of fecal bacteria in polluted water and its source. Their new technique detects the presence of markers - unique gene sequences from specific strains of bacteria - found in host species such as humans or cows.
Until a few years ago, it was impossible to pinpoint specific causes of fecal contamination, which can come from any number of sources. Septic tanks percolating into the groundwater, overflow from wastewater treatment plants and runoff from a confined cattle feeding operation are usual suspects for fecal contamination of water. Deer and elk droppings and waste from water birds, dogs and cats have been blamed for water pollution problems, as well.
"Traditional testing tells you that you have contamination, but not where it comes from," explained Field, a microbiologist with OSU's Agricultural Experiment Station. "The standard tests, growing fecal indicator bacteria such as E. coli, can't distinguish between human, elk, bird, cattle or pet-based fecal sources.
"And this is the kind of test that regulations are still based on," she added. "The laws have nothing to do with the source of the contamination."
Oregon's Tillamook Bay typically suffers chronic "non-point" fecal contamination that periodically poses risks to human health and the area's shellfish industry. Previously, no one could really pinpoint the source of the water pollution problem, beyond the association with coliform bacteria, found in all warm-blooded animal feces. Field chose this coastal region to try out her new techniques and help ease a local environmental health problem.
Results showed that in the majority of the Tillamook watershed, cows were the most important source of contamination, although human sewage was occasionally a problem, especially in the bay and near the towns, she said.
Now that the sources of contamination are confirmed, the Tillamook Bay community can clean it up and prevent a problem from happening again.
"Now managers on the North Coast can focus on fixing the big problems - mitigating runoff from cattle, fixing fences, and improving drainage problems," said Field.
Field's group has developed genetic markers for bacteria from a number of host species. They can now assay polluted water samples directly for the presence of the marker genes, revealing the source of the fecal contamination. Their technique has been able to detect the difference between fecal anaerobic bacteria from humans, cows (and other ruminants), dogs, pigs, horses and elk.
With a new patent, Field is now focusing on developing a simple kit that contains everything needed to perform the test. She also wants to expand the number of genetic markers, eventually to include all the animals likely to be a source of contamination, even marine mammals and wild birds.
Dogs, she noted, are a major issue for urban non-point source fecal pollution and cat litter has been implicated in a die-off of sea otters in northern California.
Field's research was funded by a grant from Oregon Sea Grant.
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