Equine E. coli carrying CTX-M-1 on IncHI1

IncHI1 plasmids are infrequently reported as carriers of Extended Spectrum beta-Lactamase (ESBL) genes. In this study we show that IncHI1 plasmids carrying ESBL genes are abundant in Dutch horses and the majority was carried by the dominant Escherichia coli ST1250 and single or double-locus variants. The successful dissemination among horses of IncHI1 belonging to plasmid MLST type ST9, and the acquisition of an operon involved in the fructooligosaccharide metabolism suggest potential co-selection by feed components.