Drought may be accelerating the spread of antibiotic resistance through a largely overlooked pathway: the soil beneath our feet.
The study, which was conducted by researchers at the California Institute of Technology (Caltech), finds that drought is associated with elevated antibiotic resistance in soils.
The study, published last month in Nature Microbiology, says drying environments can intensify the evolution of drug-resistant bacteria, potentially linking climate change to one of the world’s most pressing health threats: Antimicrobial resistance (AMR), a process in which microbes evolve to withstand drugs designed to kill them.
The United Nations estimates that drug-resistant infections currently cause around one million deaths annually, a figure projected to rise sharply in the coming decades. Bangladesh also faces similar challenges. Data from the World Health Organization’s Global Antimicrobial Resistance Surveillance Report 2025 show that antibiotic resistance is rising in many regions, with some bacteria showing resistance levels exceeding 70 percent in parts of South-East Asia.
The researchers analysed soil samples collected from multiple regions worldwide and found a consistent pattern: the drier the soil, the higher the concentration of antibiotic-resistant bacteria.
According to the study, drought intensifies a natural biological process. Microorganisms in soil produce antibiotics to compete with one another. As soil dries, these naturally occurring antibiotics become more concentrated, creating an environment where only resistant strains are more likely to survive and multiply.
Dianne Newman, a co-author of the study, mentioned that drought conditions can mimic the effects of antibiotic overuse in clinical settings.
To understand whether this pattern extends beyond soil, the researchers compared environmental data with clinical records from 116 countries. They identified a strong correlation between levels of antibiotic resistance and soil aridity.
In a recent blog from Caltech, Xiaoyu Shan, who led the study, noted that human exposure to soil is constant, whether through direct contact or inhalation of dust. "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," Shan added.
For decades, efforts to combat AMR have largely focused on reducing antibiotic misuse in healthcare and agriculture. However, the findings suggest environmental factors may also play a significant role.
According to the United Nations Environment Programme (UNEP), droughts are expected to become more frequent and widespread, with projections suggesting that a quarter of the planet could experience drought-like conditions by 2050.
Although the researchers emphasise that their findings show correlation rather than direct causation, they argue the results demonstrate how climate systems and microbial ecosystems may interact to influence public health.
Scientists say further research is needed to understand how resistant bacteria move from environmental settings into human populations. The research team plans to use artificial intelligence (AI) tools next to identify and better understand the mechanisms bacteria use to resist and alter antibiotics, as per a recent blog from Caltech.
