Limited impacts of high doses of dietary copper on the gut bacterial metal resistome explain negligible co-selection of antibiotic resistance

High dietary intake of Cu has previously been linked to the selection of Cu resistance and co-selection of antibiotic re-sistance in specific gut bacteria. Based on a novel HT-qPCR metal resistance gene chip as combined with 16S rRNA gene amplicon sequencing and phenotypic resistance typing of Escherichia coli isolates, we here report the impacts of two contrasting Cu-based feed additives on the swine gut bacterial metal resistome and community assembly. DNA was extracted from fecal samples (n = 80) collected at day 26 and 116 of the experiment from 200 pigs allotted to five dietary treatments: negative control (NC) diet with 20 & mu;g CuSO4 g-1 and four diets added 125 or 250 & mu;g CuSO4 g-1 feed or 125 or 250 & mu;g Cu2O g-1 feed to the NC diet. Dietary Cu supplementation reduced the relative abundance of Lactobacillus, but it had negligible impacts on bacterial community composition relative to the gut microbiome matu-ration effect (time). The relative importance of different bacterial community assembly processes was not markedly affected by the dietary Cu treatments, and differences in swine gut metal resistome composition could be explained primarily by differences in bacterial community composition rather than by dietary Cu treatments. High dietary Cu