Dissemination of antibiotic resistance genes and their potential removal by on-farm treatment processes in nine swine feedlots in Shandong Province, China.

This work investigated the dissemination of antibiotic resistance genes (ARGs) encoding resistance to sulfonamide and tetracycline antibiotics in nine swine feedlots located in Shandong Province of China, and examined their potential removal by various on-farm treatment processes. Results indicate that the target ARGs were widely distributed in swine wastes, with mean relative abundances ranging from 3.3 × 10-5 (tetC) to 5.2 × 10-1 (tetO) in swine manure and from 7.3 × 10-3 (tetC) to 1.7 × 10-1 (tetO) in swine wastewater. The mean relative ARG abundances ranged from 9.9 × 10-5 (tetW) to 1.1 × 10-2 (tetO) in soils and from 3.1 × 10-4 (tetW) to 1.1 × 10-2 (sul2) in receiving river sediments, indicating that the farmland application of swine manure compost and the discharge of swine wastewater promoted the dissemination of ARGs into adjacent environments. Microbial fermentation bed (MFB) could reduce the relative ARG abundances by 0-1.18 logs. However, septic tank, biogas digester and natural drying methods were relatively ineffective for ARG removal, and the relative abundances of some ARGs (i.e., tetC, tetG, sul1, and sul2) even increased by 0.74-3.90 logs in treated wastes. Bacterial diversity analysis indicates that the evolution of bacterial communities in the MFB played a crucial role in eliminating the ARGs. This study helps the effective assessment and management of ecological risks arising from ARGs in swine feedlots.