Assessment of Minnesota River Antibiotic Concentrations

PROJECT OVERVIEW
The occurrences of contaminants including antibiotics, other pharmaceuticals, and personal care products in the environment have gained increasing attention in recent years because of their potential health and ecological impacts. However, serious gaps remain in our understanding of these contaminants and the significance of the threats they may pose. Through this appropriation scientists at the University of St. Thomas, Gustavus Adolphus College, and the University of Minnesota are cooperating to focus specifically on the threats posed by antibiotics to understand which antibiotics are of the most concern - for example, because of their potential to increase antibiotic resistance - and to delineate their urban and rural sources. Findings will help develop strategies to manage threats and minimize future impacts posed by antibiotics to human and ecological health.

OVERALL PROJECT OUTCOME AND RESULTS
While the presence of antibiotics in surface waters has received attention due to concerns about health or ecological impacts, major gaps still remain in our understanding of the scope and significance of this potential problem. The goal of this study was to address the question of whether human or agricultural sources of antibiotics and antibiotic resistant bacteria may be the most significant in surface waters impacted by both. We focused on drainage ditches that receive farm runoff and municipal wastewater treatment plant effluents as possible sources for a portion of the Minnesota River in Southern Minnesota.

We studied four major classes of antibiotics used in agriculture (for veterinary purposes or as growth promoters) as well as in human medicine. We conducted 12 sampling campaigns over a 28-month period from 2011 - 2013, a time period that included extremely wet and dry seasons and therefore highly variable water levels. We collected samples from two agricultural drainage ditches, two municipal wastewater treatment plants, four locations in the river (upstream of both treatment plants, between the two plants, at the outfall of the second plant, and downstream of both plants), and from a nearby reference creek site. For collected samples we quantified six antibiotic resistance genes, susceptibility of cultivable bacteria to four antibiotics, and concentrations of six antibiotics.

The highest levels of antibiotics and antibiotic resistance were consistently associated with the municipal wastewater treatment plant samples. In addition, tetracycline-resistant bacteria isolated from wastewater treatment plants were found to be much more likely (103 out of 124 isolates) than tetracycline-resistant bacteria isolated from the river (0 out of 148 isolates) to have an integron, a mobile genetic element that can be associated with multiple-antibiotic resistance. These findings suggest human sources are much more significant than agricultural sources for this portion of the Minnesota River.

PROJECT RESULTS USE AND DISSEMINATION
The students who have been involved in this project have made multiple poster presentations in local venues on their work over the course of the project. In addition, the results have been disseminated via multiple poster and oral presentations at professional conferences. It is also anticipated that manuscripts currently in preparation will result in two peer-reviewed publications in scientific journals.