In urban community gardens, rows of kale and lettuce rise incongruously between roadways and brick buildings. Food growing where it’s least expected is both inspiring and nutritious to urbanites far removed from America’s agricultural roots. But to Ryan Blaustein, assistant professor of Nutrition & Food Science at the University of Maryland, the real story lies in the soil and water beneath those greens: a hidden microbial battlefield shaping food safety, human health, and the future of urban agriculture.
Blaustein is part microbial ecologist, part genomic detective, and his research asks a simple but urgent question: How do microbes, especially antibiotic-resistant ones, move through urban soils, water, and food systems—and how can we keep them in check?
“Antimicrobial resistance is a global health threat in which microbes like bacteria and fungi lose their susceptibility to drugs, making some illnesses difficult to treat,” Blaustein said. “Although it is more frequent now from the overuse of some medications, antimicrobial resistance develops naturally, wherever microbes are found. And there are a lot of microbes found in soils.”
Impacts of the Microbe War
You can think of microbial communities as a collection of interacting species that sometimes go to war, developing antimicrobial weapons to defeat their neighbors, and antimicrobial resistance to defend themselves. When antibiotics and other human-made antimicrobials end up in soil—through animal waste on farms, and wastewater or improper disposal of antibiotics in urban settings—it’s natural for the microbes in the soil to develop defenses against them, too. But it’s unclear how often that happens on urban farms or whether it poses a threat to the food system. Urban soils can also carry a toxic legacy of road salts, engine oils, industrial byproducts, and other things that can affect the bacteria in the soil. Add in composts or treated manure that gardeners use to boost fertility, and urban farm soils present a complex stew of risk and reward. The rewards, of course, is easy access to fresh produce in underserved neighborhoods, connecting people to farming, increasing green space, and building more resilient food systems. The risks are largely unknown. That’s where Blaustein’s research comes in.
Mapping a Hidden Terrain
Blaustein and his team work with urban farms and community gardens around Washington, D.C. and in Maryland, sampling soil, irrigation water, compost, and produce to learn what microbes are present, what antimicrobial genes they carry, and how they all interact.Recent studies showed that treatments like compost may act like a probiotic for soil: boosting beneficial or benign microbes that crowd out antimicrobial-resistant ones. Blaustein’s work also revealed potential trouble spots where more studies and continued monitoring are needed. Genes for multi-drug resistance were still widespread among microbes in urban farm soils. Although none belonged to known foodborne pathogens, such genes could possibly jump to human pathogens that show up in the food system like E. coli or Salmonella.
The immediate danger to consumers is low, Blaustein said, but his work is critical for understanding potential reservoirs of resistance that could one day seed trouble in the food system. In other studies, he found that microbes, nutrients, and water chemistry in ponds used to irrigate crops shifted not just by water depth or location but over time, even within a single day.
“The when and where of water sampling matters,” Blaustein said, noting that smarter sampling strategies might let farmers and regulators detect foodborne pathogen risks from irrigation water more reliably.
Connecting The Players
Sitting at the intersection of ecology, food safety, and public health, Blaustein’s work offers a framework for designing soil management, irrigation practices, and monitoring protocols that keep produce safe and soils healthy. As antibiotic resistance grows globally, his research helps reveal how microbes move, mutate, and respond to management practices and how resistance behaves—not in hospitals or livestock barns, but where people grow food in backyards, rooftops, and city lots. He and his team are helping cities grow food that’s not just fresh—but safe.
by Kimbra Cutlip
Ryan Blaustein is part microbial ecologist, part genomic detective, and his research asks a simple but urgent question: How do microbes, especially antibiotic-resistant ones, move through urban soils, water, and food systems—and how can we keep them in check?