Swine waste: A reservoir of high-risk blaNDM and mcr-1.

Multidrug resistance associated with pigs not only affects pig production but also threatens human health by influencing the farm surrounding and contaminating the food chain. This paper focused on the occurrence and prevalence of high-risk resistance genes (using blaNDM and mcr-1 as marker genes) in two Chinese swine farms, and investigated their fate and seasonal changes in piggery wastewater treatment systems (PWWTSs). Results revealed that blaNDM and mcr-1 were prevalent in both confined swine farms, and even prevailed through various processing stages of PWWTSs. Moreover, the abundance of blaNDM and mcr-1 in winter was higher than that in summer, with 0.01-1.01 logs variation in piggery wastewater. Of concern is that considerable amounts of blaNDM and mcr-1 were present in final effluent that is applied to farmland (up to 102-104copies/mL), raising the risk of propagation to indigenous bacteria. Worse still, those pig-derived isolates harboring the blaNDM/mcr-1 gene were confirmed to spread multidrug resistance to other bacteria, which further increased their dissemination potential in agricultural environment. This study highlights the prevalence of blaNDM and mcr-1 in swine farms, meanwhile, also emphasizes the necessary to mitigate the release and propagation of these high-risk genes from swine farms following land fertilization and wastewater usage.