Spotlight on Research: UM study finds despite state of the art efforts, even the cleanest wastewater contains "super bacteria"

A new University of Minnesota study finds that the release of treated municipal wastewater—even wastewater treated by the highest-quality treatment technology—can have a significant effect on the quantities of antibiotic-resistant bacteria in surface waters.

Many of these bacteria are simultaneously resistant to different kind of antibiotics, leading experts to call these pesky bacteria ‘super bacteria’.
Antibiotic resistant bacteria develops in the intestinal track of people taking antibiotics; they are expelled with human waste, passing through the sewer systems and into municipal wastewater treatment facilities

The research was led by Tim LaPara, a University of Minnesota associate professor of civil engineering and Water Resources Science (WRS) graduate program instructor. The research was part of a WRS graduate program project in environmental microbiology.

LaPara’s team focused on the municipal wastewater in Duluth by gathering water samples from the St. Louis River, Duluth-Superior Harbor, and Lake Superior in northeastern Minnesota. Duluth’s wastewater treatment facility is considered top-of-the-line—it’s one of only a few in the country that filters water through a mixed media filter of anthracite coal, silica sand, fine garnet and gravel to remove additional particles of bacteria and nutrients.

LaPara’s team took water samples in several places to pinpoint where antibiotic- resistant bacteria were present at elevated levels. While the levels of overall bacteria were still relatively low in the surface water samples, researchers found that antibiotic-resistant genes and human-specific bacteria were at least 20-fold higher at the site where treated wastewater was released into the Duluth-Superior Harbor compared to nearby surface water samples. They concluded that the wastewater treatment outfall was the primary source of antibiotic-resistant genes in the harbor.

The study also suggests that wastewater treated using standard technologies probably contains far greater quantities of antibiotic-resistant genes, but this likely goes unnoticed because background levels of bacteria are normally much higher than in the water studied in this research.

While there’s been increasing focus on environmental reservoirs of antibiotic resistance over the past several years, the role of treated municipal wastewater has received little attention. “Current wastewater treatment removes a very large fraction of the antibiotic resistance genes,” LaPara said. “But this study shows that wastewater treatment operations need to be carefully considered and more fully studied as an important factor in the global ecology of antibiotic resistance.”



Members of LaPara's research team aboard the University's Research Vessel Blue Heron.