The insufficient extraction of DNA from swine manures may underestimate the abundance of antibiotic resistance genes as well as ignore their potential hosts.

Abstract Swine manure is considered as an extensive reservoir of antibiotic resistance genes (ARGs) spreading in the natural environment after application in soils. To understand whether ARGs abundance in swine manure is underestimated and the hosts are ignored, this study successively extracted DNA from swine manure six times and determined the abundance of several ARGs, class I integron (intI1), and 16S rRNA as well as the microbial communities. It is found that successive six DNA extraction of swine manures elevated the yield of DNA and strongly increased the abundance of ARGs, intI1, and 16S rRNA. Compared with single DNA extraction, the most dominant bacterial phylum in swine manures shifted from Proteobacteria to Firmicutes, and the dominant bacterial genera changed from Acinetobacter Clostridium after six DNA extraction. The ignored abundance of bacterial phylum and genus emphasized the possible hosts carrying these genes should be paid more attention. It is suggested that the successive DNA extraction of manures is required in the future study to improve the knowledge of estimating the risk and hosts of ARGs in manures entering the environment.