blaCTX-M-65 is carried by a Tn1722-like element on an IncN conjugative plasmid of ST131 Escherichia coli

Abstract

Escherichia coli clinical isolate WCE307 was found to belong to phylogroup B2, O25b and sequence type (ST) 131 and had blaCTX-M-65, which was carried by an IncN conjugative plasmid, pWCE307. On pWCE307, the ISEcp1Δ-blaCTX-M-65-IS903D-ironΔ structure was located in a Tn1722-like element flanked by 5 bp direct target repeats. This context was highly similar to that on pKC396, an IncN plasmid from E. coli isolate KC396 of ST131 from Germany. The Tn1722-like elements carrying blaCTX-M-65 on pWCE307 and pKC396 are likely to be hybrids of Tn1722 and Tn5051, resulting from double crossover at the res sites and the tnpA genes. The left end of the Tn1722-like elements was partially missing. As ISEcp1 and Tn1722 were both incomplete, blaCTX-M-65 might have been trapped in this context. A plasmid multilocus sequence typing (pMLST) scheme with five targets, repN, stbB, traI, traB and the korB-orfI spacer region, was developed for IncN plasmid typing. pMLST revealed that the five alleles of pWCE307 and pKC396 were identical, indicating that WCE307 and KC396 are likely to have originated very recently from a common strain, suggesting the international spread of blaCTX-M-65 mediated by ST131 E. coli.