Research indicates that enhancing the health of urban soils with compost and treated manure can, in certain instances, decrease the presence of harmful and antibiotic-resistant bacteria.
Urban soils frequently harbor chemical pollutants like heavy metals and small quantities of antibiotics, along with elevated levels of antibiotic-resistant bacteria. Recent findings from the University of Maryland hint that improving urban soil health using compost and treated manure might help lower the levels of “bad” bacteria. Grasping these insights is crucial for ensuring the safety and quality of fresh produce in urban agricultural practices. This study was published online on July 13, 2024, in the Journal of Food Protection.
“Urban agriculture fosters community engagement and now reveals its potential to enhance environmental health, particularly concerning certain antibiotic-resistant bacteria,” stated Ryan Blaustein, an assistant professor in the Department of Nutrition and Food Science at UMD and one of the study’s authors. “Cultivating crops organically may lead to healthier vegetable ‘microbiomes’ that we consumers encounter.”
Urban farmers and community gardeners commonly enhance their soils with biological additives such as animal manure or compost derived from a blend of plant materials and food remnants, including fruits, vegetables, eggs, dairy, meat, or shellfish waste. These soil enhancements are subject to regulations and must undergo proper composting or pasteurization beforehand to mitigate the risk of introducing pathogens like salmonella and E. coli, which can cause foodborne diseases. However, the effects of these organic soil improvements on antibiotic resistance within urban food systems are not well understood.
To explore this issue, Blaustein and his team examined soil and leafy greens like kale and lettuce from seven urban farms and community gardens in Washington, D.C. They assessed the total bacterial content and the presence of bacteria resistant to antibiotics such as ampicillin and tetracycline. Each site included tests on leafy greens alongside treated and untreated soil samples.
The findings revealed that soils enhanced with manure or compost contained a significantly higher total bacterial count compared to untreated soils, but did not show elevated levels of harmful bacteria or antibiotic-resistant strains. In fact, the ratio of resistant bacteria and food safety indicators was comparatively lower in the amended soils. While further research is necessary to understand the long-term effects, the results imply that manure and compost may serve a probiotic role for soils, possibly introducing or nurturing beneficial bacteria that outcompete and suppress antibiotic-resistant bacteria.
Furthermore, the researchers noted a strong correlation between soil pH levels and the concentration of tetracycline-resistant bacteria, indicating that pH management could be significant for mitigating associated risks. Notably, the researchers discovered substantial variations in bacterial levels across different sites, sometimes even on the same farm, influenced by the types of amendments applied and the varieties of greens cultivated. Blaustein emphasized that these findings underscore the necessity of developing a comprehensive understanding of soils in urban agricultural settings.
This information is vital for recognizing the benefits of compost and manure in enhancing soil health, managing harmful bacteria, and ensuring a safe food supply in urban agricultural environments.
