Rivers and streams could be a major source of antibiotic resistance in the environment.

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Scientists from Warwick’s School of Life Sciences and the University of Exeter’s Medical School who were studying the River Thames found greater numbers of antibiotic resistant bacteria near waste water treatment works.

The scientists said the growing problem of antibiotic resistance is “one of the largest threats to human health for a century.” UK chief medical officer Professor Dame Sally Davies has said that the threat of antimicrobial resistance is equal to that posed by climate change.

The researchers from Warwick and Exeter said increasingly large amounts of antibiotics are being released into the environment through both human and agricultural use, and highlighted surface run off from farming (including fertiliser and animal slurry) being washed into rivers as a worry.

Professor Elizabeth Wellington of the University of Warwick, said, "Antibiotic resistance naturally occurs in the environment, but we don't yet know how human and agricultural waste is affecting its development. We've found that waste water discharges effect resistance levels and that improvements in our treatment processes could hold the key to reducing the prevalence of resistant bacteria in the environment."

The work also showed that different types of waste water treatment plants release varying amounts of resistant bacteria, and revealed an association between the presence of certain compounds in waste water - including zinc, phosphorous and silicon - and antibiotic resistance.

Dr William Gaze, who also worked on the study, said, “We think those bacteria that have developed to survive in environments rich in metals may also possess antibiotic resistance mechanisms - highlighting the complexity of this global issue."

The team also found that several other factors affected the prevalence of antibiotic resistance, such as changes in rainfall and land cover. For example, heavy rainfall at a point along the river surrounded by grassland raised resistance levels; whereas a heavy rainfall at a point surrounded by woodland reduced the levels seen.

They said increased levels of antibiotic resistance in the aquatic environment could lead to increased risk of human exposure, though they claimed more research is needed.