The integrative and conjugative element ICECiPOL15 mediates horizontal transfer of β-lactam resistance gene in Chryseobacterium indoltheticum POL15

•Drug-resistant Chryseobacterium indoltheticum POL15 was found in farm wastewater.•A novel integrative and conjugative element ICECiPOL15 was identified in strain POL15.•ICECiPOL15 carries a β-lactamase gene and mediates β-lactam antibiotic resistance.•ICECiPOL15 might have evolved from other Chryseobacterium species.•ICECiPOL15 is capable of horizontal transfer to Escherichia Coli. The dissemination of antibiotic resistance genes (ARGs) from the environment, including agricultural sources, is of increasing concern. In this study, we examined the antibiotic resistance profile and genomic sequence of a strain of Chryseobacterium indoltheticum obtained from an agricultural location. The multidrug-resistant bacterial strain POL15 was isolated from the wastewater of a livestock farm in China. Whole-genome sequencing was performed followed by bioinformatics analyses to identify integrative and conjugative elements (ICEs) and ARGs. Mating assays were performed to analyse ICE transferability. Whole-genome sequencing and annotation showed that the genome of POL15 encodes ARGs. Additionally, an ICE named ICECiPOL15, which carries a class C β-lactamase-encoding gene blaAQU, was identified in the POL15 genome. Genes encoding an integrase, an excisionase, a relaxase, a type IV coupling protein and conjugative transposon proteins involved in a type IV secretion system were also identified in ICECiPOL15. Sequence alignment revealed that ICECiPOL15 might have evolved from other Chryseobacterium species. The horizontal transferability of ICECiPOL15 was demonstrated by mating experiments between C. indoltheticum POL15 and Escherichia coli DL21. This study represents the first characterization of a mobilizable antibiotic resistance ICE in a species of C. indoltheticum and provides evidence that C. indoltheticum strains could be important reservoirs and vehicles for ARGs on livestock farms.