Aggregation of Antibiotic Resistance Plasmids under Different Hydrochemical Conditions
The excessive and uncontrolled use of antibiotics inevitably leads to their release into natural environments, accelerating the production, occurrence, and transport of resistant bacteria and resistance genes. Among these, antibiotic resistance plasmids (ARPs) pose a significant public health challenge due to their environmental persistence and ability to spread and amplify within microbial communities. This study used the tetC gene-pUC18 plasmid as a model ARP to investigate aggregation behavior in aqueous environments under varying pH (3–7), ionic strength (0.001–0.1 mol·L−1 NaCl and 0.001–0.05 mol·L−1 CaCl2), and in the presence of different concentrations of natural colloids. Results indicate that at low pH, ARP structure condenses inward and functional groups may protonate, reducing negative charge and overall size. Compared to Na+, Ca2+ forms cationic bridges between negatively charged phosphate diester groups, significantly enhancing aggregation. Natural colloids induce heteroaggregation with ARPs, with aggregate size increasing with colloid concentration. This study provides scientific evidence for elucidating ARP behavior in soil and groundwater, crucial for assessing risks to human health and ecosystems and understanding global circulation mechanisms.