Abstract
In this study, we examined the types of antibiotic resistance genes (ARGs) possessed by bacteria and bacteriophages in swine feedlot wastewater before and after treatment using a metagenomics approach. We found that the relative abundance of ARGs in bacterial DNA in all water samples was significantly higher than that in phages DNA (>10.6-fold), and wastewater treatment did not significantly change the relative abundance of bacterial- or phage-associated ARGs. We further detected the distribution and diversity of the different types of ARGs according to the class of antibiotics to which they confer resistance, the tetracycline resistance genes were the most abundant resistance genes and phages were more likely to harbor ATP-binding cassette transporter family and ribosomal protection genes. Moreover, the colistin resistance gene mcr-1 was also detected in the phage population. When assessing the contribution of phages in spreading different groups of ARGs, β-lactamase resistance genes had a relatively high spreading ability even though the abundance was low. These findings possibly indicated that phages not only could serve as important reservoir of ARG but also carry particular ARGs in swine feedlot wastewater, and this phenomenon is independent of the environment.
Highlights
The over-reliance and over-use of antibiotics in humans, animals and agriculture has resulted in widespread dissemination of antibiotic resistant bacteria (ARB) and associated antibiotic resistance genes (ARGs)
As an important reservoir of ARGs, a thorough insight into phage contribution to antibiotic resistance will be of great importance in animal-associated environments, especially the water samples related to swine feedlot wastewater treatment that may have a significant impact on the surrounding environment
As an adjunct wastewater treatment system, the relative phage ARG abundance (0.001%) in the pond water was 55.7-fold lower than in the bacterial DNA fractions (0.0557%) (Figure 2). These results indicate that the swine feedlot wastewater treatment system did not significantly decrease the abundance of ARGs
Summary
The over-reliance and over-use of antibiotics in humans, animals and agriculture has resulted in widespread dissemination of antibiotic resistant bacteria (ARB) and associated antibiotic resistance genes (ARGs). The ARB and ARGs could be horizontal transferred by air and water throughout the multiple transmission mechanisms such as transformation, conjugation, and transduction (Andersson and Hughes, 2010; McEachran et al, 2015; Rodriguez-Mozaz et al, 2015; Wang et al, 2015), these processes will further led to an indirect adverse effect to the surroundings ecosystems In these transmission processes, the most studied modes are transformation and conjugation, which are mediated by transposons, integrons and plasmids (Harmer et al, 2014; Gillings et al, 2015; Sun et al, 2016). As an important reservoir of ARGs, a thorough insight into phage contribution to antibiotic resistance will be of great importance in animal-associated environments, especially the water samples related to swine feedlot wastewater treatment that may have a significant impact on the surrounding environment
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