E. coli, Enterococci and the Beach Nuisance
"Water Contact Not Recommended" – talk about a buzz-kill! This bummer advisory shows up along Lake Superior's coast when the Minnesota Department of Health (MDH) determines that Escherichia coli levels have exceeded state and federal standards.
There's a problem with using E. coli bacteria as an indicator for diarrhea-inducing (or worse) pathogens associated with human fecal contamination, however. It isn't likely to harm you nor does it necessarily indicate that there are elements in the water that will.
More often than not waterfowl, other animals and non-point sources contribute the bacteria being counted during Lake Superior's short swim season1,2. Water sullied by waterfowl might be nasty, but it is not a serious human health concern.
Additionally, in the years since the EPA developed the nation's coastal beach bacteria standards (1986), it has been well documented that E. coli live and reproduce beyond vertebrate guts. Researchers have found E. coli living the good life in sand and sediments throughout the Great Lakes and the world 1,2,3,4,5.
The beastly E. coli O157:H7 strain that haunts our food supply and news reports is extremely rare among an extensive list of benign E. coli strains retrieved from Great Lakes beaches4. In a Minnesota Sea Grant study conducted on a Lake Superior beach within Duluth's city limits, researchers found that only one out of 3557 strains of E. coli could potentially act as a human pathogen1.
Recognizing that counting E. coli colonies is a sketchy way to assess health risks for beachgoers, in 2012 the U.S. Environmental Protection Agency (EPA) proposed that beach monitoring programs consider using molecular biology tools to measure enterococci, another type of intestinal bacteria common to warm-blooded animals. Studies showed that the presence of enterococci is closely correlated with cases of gastroenteritis reported by swimmers, even more so than the presence of E. coli.
However, new research shows that, just like E. coli, enterococci species live and reproduce in sand and sediment5,6. In a study funded by Minnesota Sea Grant, researchers from the University of Minnesota examined the density, species composition, and persistence of enterococci in Lake Superior's sand, sediment, water, and soil samples6. After regularly sampling for two years at two sites from May to September they found enterococci in 149 (94%) of the samples. The concentration of enterococci generally increased as the summer progressed then fell as Old Man Winter presumably knocked them back. The results suggest that some enterococci persist and grow along the Lake Superior coastline, especially in soil.
Michael Sadowsky, Professor in the University of Minnesota's Department of Soil, Water and Climate, and Director of the University's BioTechnology Institute, is a world leader in microbial source tracking, or in other words, "figuring out the sources of fecal contamination." He said, "The presence of E. coli or enterococci doesn't mean you are going to get sick. The nation's beach standards err on the side of caution with the consequence being that beaches will be closed more often. At this time, beach monitoring programs lump bacteria together without knowing where the bacteria came from. Once we are better able to determine the sources of contamination, we'll be better able to determine the risk to human health."
Sadowsky said that the EPA's recommended standards for beach bacteria have focused on E. coli and enterococci because these bacterial proxies meet the important criteria of being cheap, easy and quick to find in 100 ml of water. Tracy Bone, Environmental Scientist with the EPA's Office of Science and Technology said the EPA hoped that research would have yielded a better way to determine health risks on beaches, but for now—and into the foreseeable future—E. coli and enterococci will have to suffice.
The EPA issues beach monitoring recommendations under the authority of the Clean Water Act as amended by the Beaches Environmental Assessment and Coastal Health (BEACH) Act of 2000. Studies dating back to the '60s have informed these recommendations, which were developed in 1986 and updated last year7. The recommendations are designed to protect swimmers, surfers, divers and others recreating along the nation's coastlines.
The BEACH Act also provides funds for monitoring coastal recreation waters and for notifying the public. The MDH taps these funds to administer the beach
monitoring program along Lake Superior, Minnesota's only qualifying coastline.
The MDH or County Health Department staff will post "Water Contact Not Recommended" advisories in the following instances: A single water sample returns levels exceeding 235 E. coli colonies per 100 ml of water; a 5-sample average taken within 30 days is greater than 126 E. coli colonies per 100 ml of water.
If the E. coli is of human origin, the EPA Office of Water estimates that 36 out of 1000 people ingesting such water could experience the unfortunate effects of diarrhea, vomiting, nausea and stomach ache. According to EPA reports associated with the updated recommendations, viruses are responsible for most of the illnesses that are contracted in recreational waters sullied by human fecal matter7.
Water contact advisories around the shores of Lake Superior signal a risk but the beach isn't closed; you can still revel in the water if you so choose. Find the MDH monitoring results on the MNBeaches website (www.mnbeaches.org), which is a collaborative effort between the University of Minnesota Duluth's Natural Resources Research Institute, the Minnesota Pollution Control Agency, and the MDH.
Useful Beach Bacteria Monitoring Links
- Minnesota Lake Superior Beach Monitoring Program
- Minnesota Department of Health, Beaches and Recreational Waters in Minnesota
- Environmental Protection Agency, Beaches
1 JR533. Ishii, S., Hansen, D.L., Hicks, R.E., and Sadowsky, M.J. 2007. Beach sand and sediments are temporal sinks and sources of Escherichia coli in Lake Superior. Environmental Sci. and Tech. 41(7): 2203-2209
2 JR537. Ksoll, W.B., Ishii, S., Sadowsky, M.J., and Hicks, R.E. 2007. Presence and sources of fecal coliform bacteria in epilithic periphyton communities of Lake Superior. Applied and Environmental Microbiology 73(12): 3771-3778.
3 JR548. Ishii, S., Sadowsky, M.J. 2008. Escherichia coli in the environment: Implications for water quality and human health. Microbes and Environments. 23(2): 101-108.
4 Bauer, L. and Alm, E. 2012. Escherichia coli toxin and attachment genes in sand at Great Lakes recreational beaches. J. Great Lakes Research 38(1): 129–133.
5 JR606. Eichmiller, J.J., Hicks, R.E., and Sadowsky, M.J. 2013. Distribution of genetic markers of fecal pollution on a freshwater sandy shoreline in proximity to wastewater effluent. Environmental Sci. and Tech. 47: 3395-3402.
6 JR604. Ran, Q., Badgley, B.D., Dillon, N., Dunny, G.M., and Sadowsky, M. 2013. Occurrence, genetic diversity, and persistence of enterococci in a Lake Superior watershed. Applied and Environmental Microbiology. 79(9): 3067-3075.
7 U.S. EPA Office of Water. 2012. Recreational Water Quality Criteria.
By Sharon Moen