Short communication Limited similarity between plasmids encoding CTX-M-1 b-lactamase in Escherichia coli from humans, pigs, cattle, organic poultry layers and horses in Denmark Lotte Jakobsen a,1, *, Valeria Bortolaia b,1 , Eliza Bielak c,1 , Arshnee Moodley b , Stefan S. Olsen a , Dennis S. Hansen d , Niels Frimodt-Møller e , Luca Guardabassi b , Henrik Hasman c a Microbiology and Infection Control, Statens Serum Institut, 5 Artillerivej, DK-2300 Copenhagen S, Denmark b Department of Veterinary Disease Biology, University of Copenhagen, Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark c National Food Institute, Technical University of Denmark, 204 Kemitorvet, DK-2800 Kgs., Lyngby, Denmark d Department of Clinical Microbiology, Copenhagen University Hospital Herlev, 75 Herlev Ringvej, DK-2730 Herlev, Denmark e Department of Clinical Microbiology, Copenhagen University Hospital Rigshospitalet, 9 Blegdamsvej, DK-2100 Copenhagen, Denmark 1. Introduction Escherichia coli producing extended-spectrum b-lactamase (ESBL) of the CTX-M type is among the fastest growing resistance problems both in community- and hospital-acquired infections worldwide. Zoonotic transmission of CTX-M-1 has been suggested based on the relative frequency of this CTX-M type among E. coli isolates of animal origin. A Dutch study showed some degree of genetic relatedness between ESBL- producing E. coli isolates from patients, poultry and retail chicken meat, and detected bla CTX-M-1 on the same plasmid incompatibility group (IncI1) among human and animal isolates [1]. In contrast, a similar study from the UK found no association between CTX-M-producing E. coli isolated from poultry and human patients, clearly indicating geographical variations in the epidemiology of CTX-M, even between closely located countries [2]. In Denmark, a nationwide prevalence study of ESBL-producing E. coli in urine and blood from hospitals and the community conducted in 2007 showed that CTX-M-15 was Journal of Global Antimicrobial Resistance 3 (2015) 132–136 A R T I C L E I N F O Article history: Received 16 December 2014 Received in revised form 10 February 2015 Accepted 10 March 2015 Keywords: Escherichia coli CTX-M-1 IncI1 IncN Plasmid sequencing Humans and animals A B S T R A C T CTX-M-1 is a common extended-spectrum b-lactamase (ESBL) in Escherichia coli from animals and is often detected among human clinical isolates. The objective of this study was to investigate the epidemiological relationship between CTX-M-1-producing E. coli isolated from patients and animals in Denmark between 2006 and 2010. In total, 65 CTX-M-1-producing isolates from patients (n = 22), pigs (n = 21), cattle (n = 4), organic poultry layers (n = 3) and horses (n = 15) were typed by pulsed-field gel electrophoresis (PFGE). Plasmids harbouring bla CTX-M-1 were characterised by S1 PFGE, PCR-based replicon typing, plasmid multilocus sequence typing, restriction fragment length polymorphism, and sequencing. Human and animal strains were unrelated based on PFGE. IncI1 was more common in human isolates (13/22) than in animal isolates (7/43), whereas the opposite trend was observed for IncN (5/22 human isolates and 24/43 animal isolates). Full characterisation of the plasmids harbouring bla CTX- M-1 revealed host-specific patterns in the distribution of plasmid types, with specific IncI1, IncN and IncH1 plasmid subtypes being predominant in humans, livestock and horses, respectively. Three indistinguishable human, bovine and porcine IncI1/ST49 plasmids had high nucleotide sequence homology and differed by the presence of IS66 elements in the bovine plasmid and the absence of one gene within the microcin-encoding operon in the human plasmid. In conclusion, this work suggests a minor contribution by animals to the occurrence of CTX-M-1 in human E. coli infections in Denmark during the study period. ß 2015 International Society for Chemotherapy of Infection and Cancer. Published by Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +45 3268 3668; fax: +45 3268 3132. E-mail address: lottejakobsen@gmail.com (L. Jakobsen). 1 These three authors contributed equally to the study and share joint first authorship. Contents lists available at ScienceDirect Journal of Global Antimicrobial Resistance jo u rn al h om ep age: w ww.els evier.c o m/lo c ate/jg ar http://dx.doi.org/10.1016/j.jgar.2015.03.009 2213-7165/ß 2015 International Society for Chemotherapy of Infection and Cancer. Published by Elsevier Ltd. All rights reserved.