Ubiquitous nanocolloids suppress the conjugative transfer of plasmid-mediated antibiotic resistance in aqueous environment.

Nanocolloids (Nc) are widespread in natural water environment, whereas the potential effects of Nc on dissemination of antibiotic resistance remain largely unknown. In this study, Nc collected from the Yellow River in Henan province was tested for its ability to influence the conjugative transfer of resistant plasmid in aqueous environment. The results revealed that the conjugative transfer of RP4 plasmid between Escherichia coli was down-regulated by 52%-91% upon exposure to 1-10 mg/L Nc and the reduction became constant when the dose became higher (20-200 mg/L). Despite the exposure of Nc activated the anti-oxidation and SOS response in bacteria through up-regulating genes involved in glutathione biosynthesis and DNA recombination, the inhibition on the synthesis and secretion of extracellular polysaccharide induced the prevention of cell-cell contact, leading to the reduction of plasmid transfer. This was evidenced by the decreased bacterial adhesion and lowered levels of genes and metabolites relevant to transmembrane transport and D-glucose phosphorylation, as clarified in phenotypic, transcriptomics and metabolomics analysis of E. coli. The significant down-regulation of glycolysis/gluconeogenesis and TCA cycle was associated with the shortage of ATP induced by Nc. The up-regulation of global regulatory genes (korA and trbA) and the reduction of plasmid genes (trfAp, trbBp, and traG) expression also contributed to the suppressed conjugation of RP4 plasmid. The obtained findings remind that the role of ubiquitous colloidal particles is nonnegligible when practically and comprehensively assessing the risk of antibiotic resistance in the environment.