High prevalence and dissemination of β-lactamase genes in swine farms in northern China.

β-Lactamase (extended-spectrum β-lactamase (ESBL)/AmpC/carbapenemase)-encoding genes, primarily discovered in clinical settings, are increasingly recovering from the environment, thus posing potential threats to public health. This paper addresses the occurrence of high-risk β-lactamase genes (bla genes) in Chinese swine farm and its surrounding farmland, and investigated their seasonal variation and fate in piggery wastewater treatment system (PWWTS) using real-time quantitative PCR. It is observed that blaTEM-1, blaGES-1,blaOXA-1 and blaAmpC were the dominant bla genes in swine farms, which were present in all pig feces, and prevailed through each treatment stage of PWWTSs. Furthermore, bla genes were more abundant in winter than that in summer, with 0.01-1.65 logs variation in swine wastewater. Troublesomely, significant bla gene levels were still discharged via the final effluents (up to 106 copies/mL) into farmland, resulting in the increase of bla gene abundance in soil (approximately 1-3 orders of magnitude). The discharge of bla genes in wastewater from swine farm highlights the need to mitigate the persistence and spreading of these elevated bla genes in agricultural systems.