Droughts may be creating the perfect conditions for antibiotic-resistant bacteria to thrive. As the frequency and severity of droughts intensify in regions like California, scientists worry about the potential impact on human health.
Throughout the world, the overuse and misuse of antibiotics have led to the emergence of antimicrobial resistance (AMR), a growing global health threat that contributes to millions of deaths every year. Environmental factors like drought may worsen this problem by altering soil ecosystems where diverse microorganisms are involved in nutrient exchange and defense against pathogens.
Over the past several decades, peptides and other substances secreted by soil bacteria have been modified and developed into modern clinical antibiotics. Under normal conditions, these natural antibiotics are diluted in soil, thereby allowing potentially sensitive bacteria to survive with weak selection pressure. During drought, reduced water content in soil concentrates microorganisms like bacteria and their antibiotic metabolites to increase selection pressure that favors the proliferation of resistant strains with potential consequences to human health.
In a recent Nature Microbiology study, researchers simulated drought conditions and assessed how antibiotic-resistant and sensitive bacterial species in soil responded. Under drought conditions, sensitive strains struggled to survive and reproduce, whereas resistant species were not affected. These findings demonstrate that the increased concentration of antibiotics within soil during drought-like conditions leads to the selective enrichment of resistant species and other functional genes that confer competitive advantages.
Metagenomic evidence confirmed that the abundance of antibiotic resistance genes in soil increases with drought due to greater selective pressure from natural antibiotics. As the duration of the drought increases, this enrichment also strengthens to further enhance fitness.
To determine whether these environmental changes extend beyond soil ecosystems, antibiotic resistance data collected from hospitals in over one hundred countries were analyzed and aggregated with corresponding climate data at each hospital’s location. As aridity index values declined, which reflects drier conditions due to lower rainfall and higher temperatures, the prevalence of antibiotic-resistant species in clinical samples increased. This negative correlation remained equally strong among all nations, regardless of economic factors and health care infrastructure.
Although drought appears to create ideal conditions for resistant bacteria in soil, it remains unclear whether these microorganisms could contribute to infections in humans or animals. The observations in this study are based on experimental and cross-sectional data, thus emphasizing the need for additional research to determine the pathways involved in antibiotic resistance gene exchange between soil bacteria and clinical pathogens.
As climate change is expected to increase the frequency and severity of droughts, these findings raise concerns about its potential to accelerate the global spread of antibiotic resistance. Monitoring the emergence of antibiotic resistance genes in soil, water, and dust, particularly in agricultural areas or hospitals, may allow scientists to mitigate antibiotic resistance before it reaches humans. The integration of environmental monitoring with hospital infection data can also guide targeted interventions and determine their effectiveness in real time.
“Every populated continent contains regions that may face a heightened risk of antibiotic resistance emergence driven by climate change.”
Benedette Cuffari is a research scientist.
