Droughts are driving the spread of antibiotic resistant infections around the world, research has shown.

Researchers from the California Institute of Technology (Caltech) analysed samples taken from around the globe and found that the more arid the soil, the greater the concentration of antibiotic resistant bacteria it contained.

Their findings, published in Nature Microbiology late last month, show that a natural selection process is effectively supercharged when soil dries up.

Naturally occurring antibiotics produced by microorganisms in the soil become more concentrated during a drought, creating conditions that favour resistant strains, they write.

Antimicrobial resistance (AMR) occurs when microbes evolve to resist the drugs used to treat infections. Drug-resistant infections already kill a million people every year and could cause 10 million deaths a year by the middle of this century, according to the United Nations.

For decades, much of the effort on tackling AMR has focused on curbing the overuse of antibiotics in healthcare, but the Caltech research suggests that natural processes could also be fuelling the phenomenon.

“Droughts are creating the same effects as overuse of antibiotics in the clinic: They both drive selection for antibiotics resistance,” said Dianne Newman, a Professor of Biology and Geobiology at Caltech and a co-author of the study.

The researchers also compared clinical surveillance data from 116 countries with data on soil conditions and identified a strong correlation between the frequency of antibiotic resistance and aridity.

“We’re interacting with soil all the time, whether it’s recreational or simply by inhaling dust,” said Xiaoyu Shan, a Caltech postdoctoral scholar who led the study.

“Importantly, bacteria are able to transfer genes to each other, and antibiotic-resistance genes are known to have a high rate of transfer. With trillions of bacteria in the environment, this is a substantial occurrence.”

Experts say the correlation should cause us to rethink the connection between the environment and antimicrobial resistance.

“This study highlights that human health and environmental health are inseparable,” said Prof Newman.

Professor Bruno González Zorn, Director of the Antibiotic Resistance Unit at the University of Madrid and a World Health Organization (WHO) adviser on antibiotic resistance, who was not involved in the study, said: “[The study] forces us to rethink antimicrobial resistance beyond hospitals and prescriptions.

“We have traditionally focused on antibiotic consumption as the main driver, but this work shows that environmental pressures – specifically drought – can also shape resistance at a global scale,” he told The Telegraph.

The study also suggests that climate change may be helping to create the ideal conditions for drug-resistant bacteria to spread – droughts are becoming more frequent and widespread, with 25 per cent of the world set to experience drought-like conditions by 2050.

While the report’s authors make clear that the link they have identified is a correlation rather than a causation, they conclude that the study “offers a clear example of how climate change has the potential to intersect with microbial ecology to shape public health outcomes”.

Dr Lindsey Ann Edwards, a Senior Lecturer in Microbiology at King’s College London, said: “Antibiotics and antimicrobial resistance didn’t begin with hospitals – they’re hundreds of millions of years old.

“Soil microbes have always produced antibiotics to compete with each other, and they’ve evolved resistance genes to protect themselves. This is the ecological process Sir Alexander Fleming rediscovered in 1928 when he noticed Penicillium mould killing nearby bacteria, but microbes had been doing this for hundreds of millions of years,” she told The Telegraph.

While more work is needed to understand how drug-resistant bacteria are moving from the soil to the clinic, “the message is clear: Climate change is shaping the evolution of antimicrobial resistance, and as drought intensifies, microbes evolve faster, and antibiotic resistance rises with them.”

Dr González Zorn, the WHO adviser, stressed the need for continued research on the impact of climate change on AMR.

“A key next step is to integrate climate variables into antimicrobial resistance surveillance. If drought can act as a selective force, then climate change becomes directly relevant to antimicrobial resistance dynamics, and this must be reflected in our monitoring systems and policies,” he said.

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