An innovative risk evaluation method on soil pathogens in urban-rural ecosystem

A case study showing highly traceable sources of bacteria on surfaces of university buildings

University students predominantly spend their time indoors, where prolonged exposure raises the risk of contact with microorganisms of concern. However, our knowledge about the microbial community characteristics on university campus and their underpinnings is limited. To address it, we characterized bacterial communities from the surfaces of various built environments typical of a university campus, including cafeterias, classrooms, dormitories, offices, meeting rooms, and restrooms, in addition to human skin. The classrooms harbored the highest α-diversity, while the cafeterias had the lowest α-diversity. The bacterial community composition varied significantly across different building types. Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Cyanobacteria were common phyla in university buildings, accounting for more than 90 % of total abundance. Staphylococcus aureus was the most abundant potential pathogen in classrooms, dormitories, offices, restrooms, and on human skin, indicating a potential risk for skin disease infections in these buildings. We further developed a new quantitative pathogenic risk assessment method according to the threat of pathogens to humans and found that classrooms exhibited the highest potential risk. The fast expectation-maximization algorithm identified 59 %-86 % of bacterial sources in buildings, with the human skin as the largest bacterial source for most buildings. As the sources of bacteria were highly traceable, we showed that homogeneous selection, dispersal limitation, and ecological drift were major ecological forces that drove community assembly. Our findings have important implications for predicting the distribution and sources of indoor dust bacterial communities on university campus.

Urbanization and land use regulate soil vulnerability to antibiotic contamination in urban green spaces

The presence of antibiotics in environment is an emerging concern because of their ubiquitous occurrence, adverse eco-toxicological effects, and promotion of widespread antibiotic resistance. Urban soil, which plays a noticeable role in human health, may be a reservoir of antibiotics because of intensive human disturbance. However, little is understood about the vulnerability of soil to antibiotic contamination in urban areas and the spatial-temporal characteristics of anthropogenic and environmental pressures. In this study, we developed a framework for the dynamic assessment of soil vulnerability to antibiotic contamination in urban green spaces, combining antibiotic release, exposure, and consequence layers. According to the results, soil vulnerability risks shown obvious spatial-temporal variation in urban areas. Areas at a high risk of antibiotic contamination were usually found in urban centers with high population densities and in seasons with low temperature and vegetation coverage. Quinolones (e.g., ofloxacin and norfloxacin) were priority antibiotics that posed the highest vulnerability risks, followed by tetracyclines. We also confirmed the effectiveness of the vulnerability assessment by correlating soil vulnerability indexes and antibiotic residues in urban soils. Furthermore, urbanization- and land use-related parameters were shown to be critical in regulating soil vulnerability to antibiotic contamination based on sensitivity analysis. These findings have important implications for the prediction and mitigation of urban soil contamination with antibiotics and strategies to improve human health.