Prevalence of bacterial resistance within an eco-agricultural system in Hangzhou, China.

The wide use of antibiotics in the animal husbandry and the relevant sustainable industries may promote the emergence of antibiotic-resistant bacteria (ARB), which constitutes a growing threat to human health. The objective of this study was to determine the abundance and diversity of sulfonamide- and tetracycline-resistant bacteria within an eco-agricultural system (EAS) in Hangzhou, China. We investigated samples at every link in the EAS, from livestock manure, to biogas residues and biogas slurry, to vegetable and ryegrass fields, to a fish pond. A combination of culture-based and 16S rRNA gene-based sequencing method was used in this study. Within the studied system, the average rate of bacterial resistance to sulfonamide (46.19 %) was much higher than that of tetracycline (8.51 %) (p < 0.01). There were 224 isolates that were enumerated and sequenced, 108 of which were identified to species level. The genera comprising the sulfamethoxazole-resistant (SMXr) bacteria were generally different from those of tetracycline-resistant (TCr) bacteria. Staphylococcus and Acinetobacter were the most dominant genera of SMXr bacteria (19.30 % of the total resistant bacteria) and TCr bacteria (14.04 % of the total resistant bacteria), respectively. Several strains of resistant opportunistic pathogens (e.g., Pantoea agglomerans) were detected in edible vegetable samples, which may exert a potential threat to both pig production and human health. In general, this study indicates that the EAS is an important reservoir of antibiotic-resistant bacteria, some of which may be pathogenic.

High-throughput profiling of antibiotic resistance genes in drinking water treatment plants and distribution systems.

Antibiotic resistance genes (ARGs) are present in surface water and often cannot be completely eliminated by drinking water treatment plants (DWTPs). Improper elimination of the ARG-harboring microorganisms contaminates the water supply and would lead to animal and human disease. Therefore, it is of utmost importance to determine the most effective ways by which DWTPs can eliminate ARGs. Here, we tested water samples from two DWTPs and distribution systems and detected the presence of 285 ARGs, 8 transposases, and intI-1 by utilizing high-throughput qPCR. The prevalence of ARGs differed in the two DWTPs, one of which employed conventional water treatments while the other had advanced treatment processes. The relative abundance of ARGs increased significantly after the treatment with biological activated carbon (BAC), raising the number of detected ARGs from 76 to 150. Furthermore, the final chlorination step enhanced the relative abundance of ARGs in the finished water generated from both DWTPs. The total enrichment of ARGs varied from 6.4-to 109.2-fold in tap water compared to finished water, among which beta-lactam resistance genes displayed the highest enrichment. Six transposase genes were detected in tap water samples, with the transposase gene TnpA-04 showing the greatest enrichment (up to 124.9-fold). We observed significant positive correlations between ARGs and mobile genetic elements (MGEs) during the distribution systems, indicating that transposases and intI-1 may contribute to antibiotic resistance in drinking water. To our knowledge, this is the first study to investigate the diversity and abundance of ARGs in drinking water treatment systems utilizing high-throughput qPCR techniques in China.

Behavior of antibiotics and antibiotic resistance genes in eco-agricultural system: A case study.

This study aims to determine abundance and persistence of antibiotics and antibiotic resistance genes (ARGs) in eco-agricultural system (EAS), which starts from swine feces to anaerobic digestion products, then application of anaerobic digestion solid residue (ADSR) and anaerobic digestion liquid residue (ADLR) to the soil to grow ryegrass, one of swine feed. Oxytetracycline had the highest concentration in manure reaching up to 138.7 mg/kg. Most of antibiotics could be effectively eliminated by anaerobic digestion and removal rates ranged from 11% to 86%. ARGs abundance fluctuated within EAS. TetQ had the highest relative abundance and the relative abundance of tetG had the least variation within the system, which indicates that tetG is persistent in the agricultural environment and requires more attention. Compared to the relative abundance in manure, tetC and tetM increased in biogas residue while three ribosomal protection proteins genes (tetO, tetQ, tetW) decreased (p<0.05), with other genes showing no significant change after anaerobic fermentation (p>0.05). Most ARGs in downstream components (soils and fishpond) of EAS showed significantly higher relative abundance than the control agricultural system (p<0.05), except for tetG and sulI.