Wastewater treatment plants in South Africa may be helping to spread antibiotic resistance into rivers and the wider environment, according to a new study.
The research, published in Cell Reports, was led by scientists from Stellenbosch University. It raises concerns that treated wastewater could still carry genetic material that allows bacteria to resist antibiotics.
Antimicrobial resistance (AMR) happens when microbes such as bacteria no longer respond to medicines used to treat infections. It is already a growing global health threat. Experts warn that if current trends continue, AMR could cause up to 10 million deaths each year by 2050.
In this study, researchers looked at how antibiotic resistance behaves in wastewater treatment plants and nearby rivers in a major South African city.
They focused on what happens during the treatment process. While treatment plants are designed to remove harmful substances and kill bacteria, they may not fully remove genetic material left behind.
Dr John Paul Makumbi, a medical microbiologist and the study’s lead author, said that antibiotic resistance is a natural process. Bacteria evolve over time to survive threats in their environment.
But in wastewater systems, this process can speed up.
Wastewater treatment plants receive a mix of waste from homes, hospitals, factories, and slaughterhouses. This creates what researchers describe as a “toxic mix” that exposes bacteria to many stress factors at once.
This environment can encourage bacteria to develop and share resistance.
The researchers collected samples from nine wastewater treatment plants and nearby rivers in the Tshwane area.
They found genetic material linked to two major groups of bacteria—Pseudomonadota and Bacteroidota—which are known for strong resistance to multiple antibiotics.
Importantly, even when bacteria were killed during treatment, their DNA remained in the water.
This leftover DNA, known as extracellular DNA, can still carry antibiotic resistance genes.
“Even though the bacteria themselves are killed, we found extracellular DNA carrying resistant genes in the effluent,” Makumbi said. “These genes could still be transmitted and shared with other bacteria in the environment.”
This means that rivers receiving treated wastewater could become hotspots where resistance spreads further.
The study suggests that wastewater treatment plants may act as “superspreaders” of antibiotic resistance in the environment.
Although some plants are being upgraded with advanced technologies such as ultraviolet (UV) treatment to reduce these risks, progress has been slow.
The researchers say more needs to be done to improve how wastewater is treated.
They recommend that waste from high-risk sources—such as hospitals, slaughterhouses, and industrial facilities—should be treated before it enters the main wastewater system.
They also call for better treatment before wastewater is released into rivers.
“If we want to protect our waterways and public health, and contain the spread of superbugs in the environment, we need to protect and upgrade wastewater treatment plants,” Makumbi said.
The study highlights a broader issue linking water quality and public health.
Professor Thulani Makhlanyane, a senior researcher involved in the study, warned that antimicrobial resistance could become a major challenge in the future, especially in regions with aging infrastructure and limited resources.
“Future wars will in part be based on water security and antimicrobial resistance,” he said. “This is especially true in Africa where aging infrastructure and poor management are compounding the problem.”
The findings add to growing evidence that the environment plays an important role in the spread of antibiotic resistance—not just hospitals and clinics.
As countries look for ways to reuse water and manage limited resources, scientists say understanding these risks will be critical.
Improving wastewater systems, strengthening regulation, and investing in research could help slow the spread of antibiotic resistance and protect both ecosystems and human health.
