[Effect of Co-composting of Chicken Manure with Chinese Medicinal Herbal Residues on Antibiotic Resistance Genes].

Abstract

Livestock manure is an important pathway by which antibiotic resistance genes (ARGs) enter the environment. To reduce the occurrence of antibiotic resistance genes in manures, we studied the variations of ARGs and mobile gene elements (MGEs) during the 46-day co-composting of chicken manure with Chinese medicinal herbal residues. The abundance of 100 ARGs and 5 MGEs were measured by Real-Time Quantitative PCR with 0, 3, 7, 14, 28, and 46 d co-composting. We detected 21 ARGs, 2 integrase genes (intI1 and intI2), and 3 transposase genes (tnpA-01, tnpA-02, and tnpA-03). The abundance of 5 MGEs significantly declined with co-composting time, particularly tnpA-01 and tnpA-02, which were reduced by two orders of magnitude. The abundance of aacA/aphD and aadE were significantly reduced (P<0.05) in aminoglycoside resistance genes. In β-lactam resistance genes, the strongest relationships were demonstrated between blaOXA1 and compost days (P=0.016), and the removal rate was 78.63%. The average removal rate was 90.39% for amide resistance genes, which decreased significantly with composting time. The removal ratios were different among tetracycline resistance genes. For example, the removal ratios of tetG and tetR were 99.77% and 31.72%, respectively. The highest removal rate of qnrD was 99.89%. The removal rate of sulⅢ was as high as 99.88%, while sulⅠ showed an increasing trend. Correlations between ARGs and MGEs were significant correlation for tnpA-01 and ARGs (P<0.05). The trend of ARGs with composting time indicates that the composting of Chinese medicine residues and chicken manure can significantly reduce the abundance of ARGs, thus reducing the risk of ARGs being distributed via livestock manure application.