Chromosomal location of blaCTX-M genes in clinical isolates of Escherichia coli from Germany, The Netherlands and the UK

This study aimed to detect and characterise clinical Escherichia coli isolates suspected of carrying chromosomally encoded CTX-M enzymes. Escherichia coli (n= 356) obtained in Germany, The Netherlands and the UK (2005-2009) and resistant to third-generation cephalosporins were analysed for the presence of ESBL-/AmpC-encoding genes within the European SAFEFOODERA-ESBL project. p-Lactamases and their association with IS26 and ISEcp1 were investigated by PCR. Isolates were typed by phylogenetic grouping, MLST and PFGE. Plasmids were visualised by SI nuclease PFGE, and the location of bla(CTX-M) genes was determined by Southern hybridisation of XbaI-,S1- and I-Ceuhdigested DNA. ESBL enzymes could not be located on plasmids in 171356 isolates (4.8%). These 17 isolates, from different countries and years, were ascribed to phylogenetic groups D (9), B2 (6) and B1 (2), and to seven sequence types, with 5T38 being the most frequent (7 phylogroup D isolates). Eleven isolates produced CTX-M-15. bla(CTX-M)15 genes were associated with ISEcp1. The remaining isolates expressed the CTX-M group 9 p-lactamases CTX-M-14 (4), CTX-M-9 (1) and CTX-M-51 (1). blacTx_m probes hybridised with I-CeuI- and/or XbaI-digested DNA, but not with SI -digested DNA, corroborating their chromosomal location. To summarise, only 4.8% of a large collection of ESBL-producing E. coli isolates harboured chromosomal blacTx_m genes. These isolates were of human origin and belonged predominantly to 5T38 and 5T131, which possibly indicates the role of these sequence types in this phenomenon. However, heterogeneity among isolates was found, suggesting that their spread is not only due to the dispersion of successful E. coli clones. (C) 2014 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.