Complete Nucleotide Sequences of Plasmids pEK204, pEK499, and pEK516, Encoding CTX-M Enzymes in Three Major Escherichia coli Lineages from the United Kingdom, All Belonging to the International O25:H4-ST131 Clone

Abstract

ABSTRACT We determined the complete nucleotide sequences of three plasmids that encode CTX-M extended-spectrum β-lactamases (ESBLs) in pulsed-field gel electrophoresis-defined United Kingdom variants (strains A, C, and D) of the internationally prevalent Escherichia coli O25:H4-ST131 clone. Plasmid pEK499 (strain A; 117,536 bp) was a fusion of type FII and FIA replicons and harbored the following 10 antibiotic resistance genes conferring resistance to eight antibiotic classes: bla CTX-M-15 , bla OXA-1 , bla TEM-1, aac6′-Ib-cr , mph (A), catB4 , tet (A), and the integron-borne dfrA7 , aadA5 , and sulI genes. pEK516 (strain D; 64,471 bp) belonged to incompatibility group IncFII and carried seven antibiotic resistance genes: bla CTX-M-15 , bla OXA-1 , bla TEM-1 , aac6′-Ib-cr , catB4 , and tet (A), all as in pEK499. It also carried aac3-IIa , conferring gentamicin resistance, and was highly related to pC15-1a, a plasmid encoding the CTX-M-15 enzyme in Canada. By contrast, pEK204 (strain C; 93,732 bp) belonged to incompatibility group IncI1 and carried only two resistance genes, bla CTX-M-3 and bla TEM-1 . It probably arose by the transposition of Tn 3 and IS Ecp1 - bla CTX-M-3 elements into a pCOLIb-P9-like plasmid. We conclude that (i) United Kingdom variants of the successful E. coli ST131 clone have acquired different plasmids encoding CTX-M ESBLs on separate occasions, (ii) the bla CTX-M-3 and bla CTX-M-15 genes on pEK204 and pEK499/pEK516 represent separate escape events, and (iii) IncFII plasmids harboring bla CTX-M-15 have played a crucial role in the global spread of CTX-M-15 ESBLs in E. coli .