Antimicrobial resistant Enterobacteriaceae are widespread in surface waters across the globe, according to a new study.

The review, ‘Freshwater environment as a reservoir of Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae’ by Dr Sohyun Cho, Dr Charlene Jackson, and Dr Jonathan Frye appears in the Journal of Applied Microbiology, an Applied Microbiology International publication.


Upper Oconee Watershed

“Surface water can be highly impacted by human activities as it receives contaminants from different sources, and the presence of ESBL-producing bacteria represents a potential public health safety risk for those exposed to surface water,” said lead author Dr. Sohyun Cho, a postdoctoral researcher at USDA-ARS.

“ESBL-producing bacteria are resistant to most β-lactam antibiotics, rendering these critical drugs ineffective and thus complicating treatment of infections. The rapid spread of ESBL-producing Enterobacteriaceae in healthcare settings and the community is a growing threat to public health, and there have been increasing reports on the prevalence and abundance of ESBL-producing Enterobacteriaceae in aquatic environments.”

Aquatic environment

“Freshwater, including rivers, lakes, and streams, is a major environmental compartment that is important for everyday human life. Surface water is prone to bacterial contamination as it receives wastes and pollutants from human and animal sources, and surface water contaminated with ESBL-producing bacteria may pose health risks to local populations exposed to the environmental water through municipal, agricultural, and recreational uses.” 

Previous studies have mainly focused on ESBL-producing Enterobacteriaceae in clinical settings, and the prevalence and trends of ESBL-producing Enterobacteriaceae in the aquatic environment were a knowledge gap that needed to be addressed. 

“We wanted to address this knowledge gap by providing a review on the current state of ESBLs in the freshwater environment, the role of the freshwater environment as a reservoir and transmission routes for ESBL-producing Enterobacteriaceae, and the impact of ESBL-producing Enterobacteriaceae present in water environments on human health,” Dr. Cho said. 

Global studies

She evaluated publications for the prevalence, diversity, and distribution of ESBL-producing Enterobacteriaceae and their genes in freshwater environments in different parts of the world.

“We also investigated their potential sources in the aquatic environment, as well as their potential drivers in the environment, including anthropogenic and environmental factors,” she said. 

“Studies conducted in various parts of the world on the prevalence of ESBL-producing Enterobacteriaceae in surface water, and the detection rates of ESBL-producing Enterobacteriaceae varied depending on geographical locations. 

“The combinations of socioeconomic and behavioral factors, such as previous use of antibiotics, international travel especially to Asia or Africa where there is high prevalence of ESBLs, overcrowded households, improper sewage disposal, and swimming in freshwater, as well as environmental factors, such as temperature, precipitation, and antibiotic residues and heavy metals accumulated in the environment, may have caused the geographical variations. 

“Studies also identify the source of ESBLs in the environment, but as surface water receives contaminants from various sources, no single source could be pinpointed. Wastewater treatment plants, agriculture, aquaculture, wild animals, and other human activities, such as raw sewage disposal, recreational activities, and religious rituals, were suggested to contribute to the presence of ESBL-producing bacteria in the aquatic environment.”

Widespread presence

The widespread presence of ESBL-producing bacteria in the environment is alarming, she said.

“They are everywhere, not only in low- and middle-income countries (LMICs), where the issue of antimicrobial resistance is a more pronounced public health problem, but also in high-income countries (HICs) where there are policies that restrict the use of antibiotics,” she said. 

“We need to reduce the spread of ESBL-producing Enterobacteriaceae in the environment in order to prevent the potential exposure and transfer to humans through consumption, irrigation, and recreation.” 

Antimicrobial resistance is a global problem that affects humans, animals, and the environment, and a clear understanding of how antimicrobial resistance spreads between these different sectors is needed, she said. 

One Health approach

“Our review highlighted the need for the One Health approach which emphasizes that the health of humans, animals, and the environment are connected, and the collaborative effort is needed to achieve the optimal health outcome for all. 

“Since studies have shown that surface water is a reservoir of ESBL-producing Enterobacteriaceae, future studies should investigate the fate and transport of these bacteria following their release into the water, as well as the impact of their presence in the environment on human health and food safety. 

“The knowledge gained should eventually be used to improve management and planning to reduce the ESBL levels in aquatic environments.”

Dr. Sohyun Cho is a postdoctoral researcher at USDA-ARS who started her PhD in microbiology with Dr. Jonathan Frye, a USDA-ARS research microbiologist in Athens, GA, to study whether the aquatic environment serves as a reservoir for antimicrobial resistant bacteria. 

Dr. Cho was supported by an Oak Ridge Institute for Science and Education (ORISE) Postdoctoral Fellowship. The project was funded by USDA-ARS and CDC.

‘Freshwater environment as a reservoir of Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae’ appears in the Journal of Applied Microbiology.

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