“Antibiotic Resistance Genes as Emerging Contaminants:
Studies in Northern Colorado”
Environmental Science & Technology A-Page Magazine
http://pubs.acs.org/journals/esthag/promo/top_papers/top2006/science3.html
Environmental Science
Second Runner-up: Antibiotic resistance genes
“Antibiotic Resistance Genes as Emerging Contaminants: Studies in Northern Colorado” by Amy Pruden,
Ruoting Pei, Heather Storteboom, and Kenneth Carlson, Colorado State University, 2006, 40 (23), 7445–
7450.
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In 2002, when environmental microbiologist Amy Pruden joined the faculty at Colorado State University,
researchers were already worried about the upward trend of concentrations of antibiotics in the
environment. Yet, no one really understood the environmental impact of these drugs. “The big question
that a lot of people are raising is: what are the actual impacts and should we care?” says Pruden. To find
the answer, Pruden teamed up with her colleague Kenneth Carlson, who had documented unnaturally
high levels of antibiotics in nearby rivers and sediments. Together they embarked on the project that led
to their ES&T paper.
Colorado State University College of Engineering
Amy Pruden (right) and Ruoting Pei collect samples from Cache la Poudre River.
Antibiotic resistance is a growing problem for human health, Pruden points out, and both the Centers for
Disease Control and Prevention and the World Health Organization are concerned. Although the
problem is largely attributed to the overprescription of antibiotics, a handful of studies have linked
overuse of antibiotics in agricultural settings to resistance in human infections. Pruden knew that
investigating the environmental impacts of antibiotics meant going to the source: antibiotic resistance
genes (ARGs) in microbes themselves.
Excessive agricultural and urban use had been shown to cause the antibiotics tetracycline (tet) and
sulphonamide (sul) to accumulate in the sediments of the Cache la Poudre River. So, Pruden and
Carlson decided to look at the levels of several tet- and sul-resistance genes in river sediments as well
as in nearby dairy lagoon water, irrigation ditch water, a wastewater recycling plant, and two drinking-
water treatment plants. (Dairy lagoons are large ponds for storing waste from dairy farms; wastewater
from the lagoons is eventually used for irrigation.)
Using a quantitative DNA amplification technique, the team measured ARG levels and found significantly
higher amounts of the genes in all sites impacted by agriculture and urban activity than the ARG levels
at a pristine site that received less effluent from urban or agricultural activities. In addition, they found a
consistent pattern in the ARG levels—the highest levels were found in dairy lagoons, followed by
irrigation ditch water and river sediments impacted by agriculture and urban activity. This suggested a
potential route by which the antibiotics and ARGs spread in the environment: from dairy farms to
irrigation ditches to rivers. Samples from the wastewater and drinking-water plants also contained high
amounts of two kinds of ARGs, tet(W) and tet(O).
“We think of contaminants as they get broken down into something worse,” says Pruden. “This is kind of
analogous: the presence of antibiotics induces the presence of these genes, which are themselves
contaminants.” Pedro Alvarez of Rice University, an expert in ARGs, says the novelty of the paper lies in
the idea that genes may be contaminants. “They had the vision to recognize that genes, genetic
elements, and genetic vectors represent an emerging class of environmental pollutants that we are
going to have to deal with,” he says.
More work still needs to be done, Pruden emphasizes. For example, just how these contaminants lead to
antibiotic-resistant infections in humans is still unknown. And future work might uncover ways to tackle
the problem “right where it is created,” says Pruden, “rather than at the hospital level [by] trying to create
more antibiotics.” —RHITU CHATTERJEE
Environ. Sci. Technol., 40 (23), 7445 -7450, 2006. 10.1021/es060413l S0013-936X(06)00413-5
Web Release Date: August 15, 2006
Copyright © 2006 American Chemical Society
Antibiotic Resistance Genes as Emerging Contaminants: Studies in Northern Colorado
Amy Pruden,* Ruoting Pei, Heather Storteboom, and Kenneth H. Carlson
Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, Colorado
80523
Received for review February 20, 2006
Revised manuscript received July 10, 2006
Accepted July 17, 2006
Abstract:
This study explores antibiotic resistance genes (ARGs) as emerging environmental contaminants. The
purpose of this study was to investigate the occurrence of ARGs in various environmental compartments
in northern Colorado, including Cache La Poudre (Poudre) River sediments, irrigation ditches, dairy
lagoons, and the effluents of wastewater recycling and drinking water treatment plants. Additionally, ARG
concentrations in the Poudre River sediments were analyzed at three time points at five sites with varying
levels of urban/agricultural impact and compared with two previously published time points. It was
expected that ARG concentrations would be significantly higher in environments directly impacted by
urban/agricultural activity than in pristine and lesser-impacted environments. Polymerase chain reaction
(PCR) detection assays were applied to detect the presence/absence of several tetracycline and
sulfonamide ARGs. Quantitative real-time PCR was used to further quantify two tetracycline ARGs (tet
(W) and tet(O)) and two sulfonamide ARGs (sul(I) and sul(II)). The following trend was observed with
respect to ARG concentrations (normalized to eubacterial 16S rRNA genes): dairy lagoon water >
irrigation ditch water > urban/agriculturally impacted river sediments (p < 0.0001), except for sul(II), which
was absent in ditch water. It was noted that tet(W) and tet(O) were also present in treated drinking water
and recycled wastewater, suggesting that these are potential pathways for the spread of ARGs to and
from humans. On the basis of this study, there is a need for environmental scientists and engineers to
help address the issue of the spread of ARGs in the environment.