By Courtney Sakry
Soil plays a much bigger role in the spread of antibiotic resistance than one might imagine. Surprisingly, the ground beneath us is packed with antibiotic resistance genes (ARGs)—tiny codes that allow bacteria to resist antibiotics. Human activities, such as pollution and changing land use, can disturb soil ecosystems and make it easier for resistance genes to transfer from soil bacteria and infect humans.
Jingqiu Liao, assistant professor in civil and environmental engineering, is on a mission to understand how soil bacteria contribute to the growing global issue of antibiotic resistance through a study recently published in Nature Communications. Her team's findings show that once bacteria acquire these resistant genes, they can be rapidly transmitted to other species as well, making this such a pressing public health threat.
Understanding these patterns can help scientists find ways to control the spread of antibiotic resistance, protecting human health and preserving the effectiveness of antibiotics for future generations.
Why antibiotic resistance in soil matters
Soil isn't just dirt—it's a bustling ecosystem filled with bacteria. Some of these bacteria naturally carry ARGs, which help them fight off antibiotics. While this might not seem like a big deal at first, it becomes dangerous when these ARGs end up in harmful bacteria that infect humans.
One such bacterium is Listeria monocytogenes. This soil dweller can make its way into the food chain and cause a serious illness called listeriosis. For people with weakened immune systems, listeriosis can be deadly, with fatality rates as high as 20% to 30%. Because of its ability to spread ARGs and infect humans, listeria is an important model for studying how antibiotic resistance develops in soil and spreads to other environments.
"Soil is an important reservoir of resistant bacteria and ARGs," Liao said. "Environmental factors can amplify ARGs by creating conditions that promote the survival, spread, and exchange of these genes among bacteria. The ecological and evolutionary mechanisms underlying the dynamics of ARGs in soils remain inadequately explored. In this project, we use listeria as a key model to understand the emergence and development of ARGs in soils."
Using listeria to study resistance
For the current study, the team members analyzed close to 600 listeria genomes from soil samples that Liao collected in a previous study, published in Nature Microbiology. They identified five main ARGs from across the United States.
The study also revealed how ARGs spread between bacteria. A process called transformation allows bacteria to pick up loose pieces of DNA containing ARGs from their surroundings. Once a bacterium acquires these genes, it can pass them along to others—even to different species. This rapid sharing of resistance genes is a major reason why antibiotic resistance is such a challenging problem.
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