Abstract: Cryptobacterium hidradiiused as a model organism, qPCR was combined with plate screening methods to demonstrate that the antibiotic-resistant genes (ARGs) donor bacteriumEscherichia coliMG1655 and the acceptor bacteriumSalmonella typhimuriumwere both able to colonize stably in the intestine. The ratio of the number of antibiotic-resistantS.typhimuriumobtained via conjugation to the number of total intestinal bacteria was used to characterize the diffusion efficiency of ARGs in the intestine. The ARG diffusion efficiency increased and then decreased with increasing tetracycline concentrations (0, 0.08, 0.4, 2, 10, and 50 mmol/L) over three days of incubation, and it peaked at 0.78% and 1.96% on the second and third days in the 0.4 mmol/L tetracycline-treated group, respectively. Moreover, the relative abundance of conjugation-relevant functional genestrfA/16S rRNAandtrbB/16S rRNAas well as activities of antioxidant enzyme in intestinal tissues shared similar trends with the ARG diffusion ratios in the gut of snails. Therefore, the present study demonstrated that a brief and low concentration of antibiotics could promote the diffusion of ARGs in the animal intestine.

Key words: Canorhabditis elegans, antibiotic-resistant gene, plasmid conjugation, tetracycline, intestinal microorganisms