S. SCHWENDENER¹, D. VOGT¹, S. N. SEIFFERT², A. ENDIMIANI², A. CARATTOLI², V. PERRETEN<sup>1

1</sup>Institute of Veterinary Bacteriology, University of Bern, Bern, Switzerland, ²Institute of Infectious Diseases, University of Bern, Bern, Switzerland

Multidrug-resistant (MDR) E. coli producing extended spectrum β-lactamases (ESBL) have been increasingly isolated in hospital, community and animals. The ESBL genes are frequently located on plasmids which can be easily transferred between bacteria. To date, only few ESBL-carrying plasmids have been completely sequenced from E. coli isolated from horses. A MDR E. coli sequence type (ST) 744 was isolated from equine wound in 2011. The E. coli strain carried the β-lactamase gene blaTEM-1 and the ESBL gene blaCTX-M-14 and nine additional acquired genes conferring resistance to chloramphenicol (catA1), trimethoprim (dfrA17), tetracycline [tet(A)], sulphonamide (sul1) and aminoglycosides [aac(3)-IIc, aadA4, aph(3')-Ia, strA and strB]. It also contained mutations in the quinolone resistance determining region of the DNA gyrase subunit A (GyrA: S83L, D87N). The β-lactamases (blaTEM-1 and blaCTX-M-14) and the aminoglycoside transferase [aac(3)-IIc] genes were solely transferred to a sensitive E. coli recipient strain by conjugation. Whole plasmid sequencing revealed the presence of these genes on a IncFII (F2:A-:B-) plasmid pKM811 with a size of 78,976 bp and an average GC content of 52%. The plasmid scaffold consists of a continuous 18,346-bp MDR region (MRR) and a 60,630-bp backbone coding for characteristic IncF plasmid functions that shared over 99% nucleotide sequence identity with the reference IncF plasmid R100. The MRR of pKM811 harbours ISEcp1-blaCTX-M-14, blaTEM-1 carried by a Tn3 fragment and a IS26 flanked aac(3)-IIc gene. The region represents a newly combined structure carrying several complete and fragmented mobile elements including four intact IS26. Identical modules containing ISEcp1-blaCTX-M-14 and a IS26-aac(3)-IIc were found on other plasmids suggesting exchange of resistance gene module by transposase and recombination between MRR of different plasmids. These resistance genes may have been selected and maintained in E. coli from equine environment where β-lactam and aminoglycoside antibiotics are frequently used for treatment.