Evolution of antibiotic resistance in the environment

Research conducted by the University of Exeter Medical School, the University of Hong Kong, and pharmaceutical company AstraZeneca revealed that low concentrations of antibiotics in the environment could be contributing to the evolution of antibiotic resistance.

The study adds to a growing concern about the environmental dimension of antibiotic resistance, and identifies the environment as a factor that needs to be seriously considered in future AMR prevention efforts – on an equal footing with antibiotic exposure in humans and animals.

Antimicrobial resistance (AMR) is recognised by the World Health Organization (WHO) as one of today’s greatest global health challenges. The organisation has warned that we may be entering an era in which antibiotics are no longer effective to cure simple, and previously treatable, bacterial infections. This would mean that currently treatable infections such as pneumonia, tuberculosis, and blood poisoning could become fatal.

The research, which was co-funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and AstraZeneca, saw Dr Aimee Murray and her colleagues expose sewage waste water to varying levels of the antibiotic cefotaxime, which WHO has listed as an “essential medicine”.

The team found that the abundance of a clinically problematic antibiotic-resistant gene blaCTX-M, increased equally at low, environmentally relevant concentrations and high, clinically relevant concentrations of cefotaxime. Previously, it had been thought more antibiotic would mean higher levels of resistance but this finding showed that may not always be the case.

The findings indicate that environments that are commonly found to have trace amounts of antibiotics, such as hospital effluent and rivers and streams that receive wastewater, could be an important, and overlooked, breeding ground for antibiotic-resistant bacteria. These bacteria can then be transmitted to humans, for example through close contact with animals, via the food we eat, or during outdoor recreational activities.

The discovery could also have clinical relevance, because during antibiotic treatment, antibiotic concentrations can be different in different parts of the body. As a result, even low levels of antibiotics in some parts of the body, like the gut, could promote evolution of resistant bacteria.

The results highlight the need for further investigation into how much environmental contamination is contributing to the evolution of antibiotic resistant bacteria, and how much of an impact it’s having on human health.

Dr Aimee Murray, of the University of Exeter Medical School, who led the research, said: “Already, some commonly prescribed antibiotics are starting to prove ineffective for some infections. Our research casts new light on how this problem may be spreading, and provides new evidence for the steps we may need to take in targeting the environment to try and stop this global problem. We also need more research to ascertain whether microbes evolve resistance to antibiotics when exposed to low levels in other settings than waste water, such as in different areas of the body.”

Professor William Gaze, of the University of Exeter Medical School, who leads the University of Exeter Medical School research programme on the environmental dimension of antibiotic resistance, said: “Our research shows just how important it is to take action to limit antibiotics entering the environment. So far a lot of research effort to tackle this problem has been around hospitals and reducing clinical prescribing, but we now know that the environment is likely to play a part in how resistance to antibiotics can evolve and spread. We all need to think more holistically about environmental management of waste, including how we treat our waste water.”

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