Swine liquid manure: a hotspot of mobile genetic elements and antibiotic resistance genes

Abstract

The overuse or abuse of antibiotics as veterinary medicine and growth promoters accelerates antibiotic resistance, creating a serious threat to public health in the world. Swine liquid manure as an important reservoir of antibiotic resistance genes (ARGs) has received much attention, but little information is known regarding the occurrence, persistence and fate of ARGs-associated mobile genetic elements (MGEs) in swine farms, especially their change patterns and removal in full-scale piggery wastewater treatment systems (PWWTSs). In this study, we searched the presence and distribution of MGEs and associated ARGs in swine farms, and addressed their fate and seasonal variation in full-scale PWWTSs by real-time quantitative PCR (qPCR). Our results revealed class 1 integrons, class 2 integrons and conjugative plasmids were prevalent in pig feces and piggery wastewater. A clear pattern of these MGE levels in swine liquid manure was also observed, i.e., intI1 > intI2 > traA (p < 0.01), and their absolute abundances in winter were all higher than that in summer with 0.07–2.23 logs. Notably, MGEs and ARGs prevailed through various treatment units of PWWTSs, and considerable levels of them were present in the treated effluent discharged from swine farms (up to 101–107 copies/mL for MGEs and 103–108 copies/mL for ARGs). There were significant correlations between most ARG abundance and MGE levels (p < 0.05), such as tetQ and traA (r = 0.775), sul1 and intI1 (r = 0.847), qnrS and inI2 (r = 0.859), suggesting the potential of ARGs—horizontal transfer. Thus the high prevalence and enrichment of MGEs and ARGs occurred in pig feces and piggery wastewater, also implicating that swine liquid manure could be a hotspot for horizontal transfer of ARGs.

Corpse Degradation of Farmed Fish Increases the Abundance of Antibiotic Resistance Genes but Exhibits the Temporal Stability

“…On the one hand, due to the extensive use of antibiotics in aquaculture (Cabello, 2006), ARGs can be transferred to from the skin, intestines and feces of dead farmed sh to water environment. On the other hand, it is reported that the spread of ARGs is closely associated with MGEs (Yang et al, 2020). And our results also showed that the ARGs' abundance was signi cantly related to MGEs.…”

Current status and future perspective of antimicrobial-resistant bacteria and resistance genes in animal-breeding environments

“…Furthermore, swine wastewater is an important source of antimicrobials in the environment, attributed to its large-scale application in the swine industry. Yang et al suggested a high prevalence of ARGs in piggery wastewater [81].…”

Antibiotic Resistance: From Pig to Meat

“…Manure can be used as fertilizer, and depending on each country's regulations, wastewater can be released into the environment in various ways. However, it has been observed that pig manure and farm wastewater can contain antibiotic residues, antibiotic resistance genes and antibiotic resistant bacteria [72][73][74]. The quantity of these components is higher when the pigs are treated with antibiotics than when the pigs are not treated.…”

“…Wastewater treatments achieved similar results [73]. Yang et al investigated two pig farm water treatment systems: one had an anaerobic tank and a ceramsite biofilter and the other had a plug flow anaerobic reactor, a temporary storage tank, a solid-liquid separation step, an upflow anaerobic sludge blanket, a primary clarifier tank, an anaerobic tank, an aerated tank and a second clarifier tank.…”

“…Yang et al investigated two pig farm water treatment systems: one had an anaerobic tank and a ceramsite biofilter and the other had a plug flow anaerobic reactor, a temporary storage tank, a solid-liquid separation step, an upflow anaerobic sludge blanket, a primary clarifier tank, an anaerobic tank, an aerated tank and a second clarifier tank. While both systems could reduce the abundance of MGEs and ARGs, the concentration in the final effluent was still considerably high after treatment [73]. Zhang et al demonstrated that treatment of wastewater by nanoscale copper was able to significantly reduce the number of both ARGs and antibiotic-resistant bacteria in wastewater [83].…”