Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. 
Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. What was studied?
The study investigated the co-occurrence of antimicrobial resistance genes (ARGs) and metal resistance genes (MRGs) in pig feces, agricultural soils fertilized with pig slurry, and sediments from aquatic environments receiving effluent from pig farms in Jiangsu Province, China. Using a metagenomic approach, the researchers profiled the abundance and diversity of ARGs, MRGs, and mobile genetic elements (MGEs) in these samples. The study also measured concentrations of ten heavy metals (including zinc, copper, chromium, and manganese) and fifteen veterinary antibiotics to determine their relationships with resistance gene abundance. The primary aim was to clarify the extent to which metals, particularly zinc used as a feed additive may facilitate the co-selection and horizontal transfer of antibiotic and metal resistance genes in pig farming environments.
Who was studied?
This research focused on environmental matrices collected from two large-scale pig farms in Jiangsu Province, China, each with a history of using zinc oxide as a feed additive and tetracycline antibiotics for disease management. Sampling included fresh pig feces (from multiple pens), agricultural soils fertilized with treated pig slurry, and sediment from ponds receiving treated slurry effluent. Ten replicate samples for each matrix (feces, soil, sediment) were collected from each farm, ensuring robust representation of the farm environments and their immediate surroundings.
Most important findings
| Critical Points | Details |
|---|---|
| Strong co-occurrence of ARGs and MRGs across all sample types | The study found significant co-occurrence between ARGs and MRGs in pig feces, soils, and sediments. Tetracycline resistance genes were most prevalent among ARGs, while zinc resistance genes dominated among MRGs. |
| Heavy metal concentrations, especially zinc, were high in pig feces and correlated with resistance genes | Zinc, copper, and cadmium levels were significantly higher in pig feces compared to soils and sediments. Zinc concentrations (824.8 mg/kg in feces) strongly correlated with the abundance of multidrug resistance genes and MGEs, suggesting zinc’s role in co-selecting for both ARGs and MRGs. |
| MGEs facilitate gene transfer and show strong correlation with both ARGs and MRGs | The abundance of specific MGEs (e.g., integrase gene intI1, insertion sequence IS981) was significantly correlated with ARGs and MRGs, indicating a high potential for horizontal gene transfer of resistance genes under metal exposure. |
| Network analysis revealed specific metals (Zn, Cr, Mn) link to ARGs and MGEs | Network analysis demonstrated that zinc co-occurred with multidrug resistance genes in feces, chromium was linked to integrase genes in both feces and soil, and manganese correlated with sulfonamide resistance genes in sediments. |
| Application of pig slurry introduces and sustains resistance genes and metals in soils and aquatic sediments | Slurry application resulted in persistent ARG and MRG presence in fertilized soils and sediments, with dominant gene types reflecting those in pig feces, suggesting ongoing risk for resistance proliferation beyond the farm environment. |
| Evidence supports zinc supplementation’s role in co-selection and spread of resistance genes | The findings strongly suggest that zinc as a feed additive contributes to the enrichment and co-selection of ARGs and MRGs, mediated by MGEs, thereby expanding the pool and mobility of resistance determinants in agricultural environments. |
Key implications
This study provides crucial evidence that zinc supplementation and heavy metal exposure in pig farms drive the co-selection and horizontal transfer of antibiotic and metal resistance genes. For heavy metal certification programs, these results highlight the need for stringent monitoring and regulation of metal additives in animal feed to minimize environmental spread of resistance.
Citation
Peng S, Zheng H, Herrero-Fresno A, Olsen JE, Dalsgaard A, Ding Z. Co-occurrence of antimicrobial and metal resistance genes in pig feces and agricultural fields fertilized with slurry. Science of the Total Environment. 2021;792:148259. doi:10.1016/j.scitotenv.2021.148259
Heavy metals are high-density elements that accumulate in the body and environment, disrupting biological processes. Lead, cadmium, arsenic, mercury, nickel, tin, aluminum, and chromium are of greatest concern due to persistence, bioaccumulation, and health risks, making them central to the HMTC program’s safety standards.
