Complete sequences of IncHI1 plasmids carrying blaCTX-M-1 and qnrS1 in equine Escherichia coli provide new insights into plasmid evolution

Objectives: To determine the structure of two multidrug-resistant IncHI1 plasmids carrying blaCTX-M-1 in Escherichia coli isolates disseminated in an equine clinic in the Czech Republic. Methods: A complete nucleotide sequencing of 239 kb IncHI1 (pEQ1) and 287 kb IncHI1/X1 (pEQ2) plasmids was performed using the 454-Genome Sequencer FLX system. The sequenceswere compared using bioinformatic tools with other sequenced IncHI1 plasmids. Results: A comparative analysis of pEQ1 and pEQ2 identified high nucleotide identity with the IncHI1 type 2 plasmids. A novel 24 kb module containing an operon involved in short-chain fructooligosaccharide uptake and metabolism was found in the pEQ backbones. The role of the pEQ plasmids in the metabolism of shortchain fructooligosaccharides was demonstrated by studying the growth of E. coli cells in the presence of these sugars. The module containing the blaCTX-M-1 gene was formed by a truncated macrolide resistance cluster and flanked by IS26 as previously observed in IncI1 and IncN plasmids. The IncHI1 plasmid changed size and gained the quinolone resistance gene qnrS1 as a result of IS26-mediated fusion with an IncX1 plasmid. Conclusions: Our data highlight the structure and evolution of IncHI1 from equine E. coli. A plasmidmediated sugar metabolic element could play a key role in strain fitness, contributing to the successful dissemination and maintenance of these plasmids in the intestinal microflora of horses. © The Author 2014.