Stormwater runoff carries antibiotic-resistance to urban beaches

Hotels 4585988
Image by Scottslm from Pixabay

SYDNEY (September 30, 2019) — Research from the University of Technology Sydney has provided clear links between stormwater discharge and the presence of antibiotic-resistant microorganisms living in urban beach habitats. The two-year study into the prevalence of antibiotic resistance (AbR) in urban coastal environments has shown elevated levels of antibiotic-resistant bacteria following rainfall on some beaches around Sydney, Australia. 

Published in Water Reseach, the study shows the exchange of antibiotic-resistance between human wastewater streams and the ecosystem and highlights the significant exposure risk to humans. According to the research, stormwater discharge (which sometimes includes combined and/or wet-weather sewer overflow events), sewage, and urban waste-stream infrastructure (such as pipes) are potential reservoirs and channels for the spread and presence of AbR microorganisms into natural coastal waters and urban beaches.  

Antibiotic resistance is a major global concern affecting medical, agricultural, urban, and natural systems, and is the consequence of the over- and misuse of antibiotics by humans, including from the overprescription of antibiotics and their overuse in farming. 

The research tracked 31 AbR genes, including ones that provide resistance to important, frontline antibiotics used in human and animal medicine. Immediately after a rainfall, the researchers found up to 100-fold increases in the abundance of several AbR genes. 

First author, Dr. Ric Carney, who conducted the research as part of his Ph.D. in the Climate Change Cluster at UTS, says the study is unique in the way that it combined an intense sampling regime with molecular biological approaches to track patterns in AbR genes at two contrasting study sites—Foreshore Beach within Botany Bay and Maroubra Beach, in southern Sydney.

"The study provides new insights into the timing and mechanisms for the input of AbR bacteria in urban beach environments regularly used by humans for recreational activities," says Carney. "The presence of AbR genes increased significantly in conjunction with storm-water input and modelled WWSO events, which occur after rainfall."

"Our results indicate that some bacteria present within urban waste streams carry AbR genes, which are subsequently washed into natural marine environments via stormwater outlets," he says.

Lead researcher, Professor Justin Seymour from the UTS Climate Change Cluster, says the observations highlighted the role of stormwater and WWSO as a means for potentially pathogenic bacteria carrying AbR genes to cross habitat boundaries.

"This research highlights the potential risk for significant levels of human exposure to antibiotic-resistant bacteria within coastal beaches that are subject to urban runoff, but the health implications of this exposure are as yet undefined," says Seymour. "However, our findings really reinforce the messages from authorities to avoid swimming in the ocean and other waterways after heavy rainfall."

"This is a global issue that will impact any urbanized coastal region, and highlights the often overlooked environmental consequences of high levels of antibiotic use by human populations," says Professor Seymour.

More in BMPs