Dissemination of clonally related Escherichia coli strains expressing extended-spectrum β-lactamase CTX-M-15

We analyzed 43 CTX-M-15-producing Escherichia coli isolates and 6 plasmids encoding the blaCTX-M-15 gene from Canada, India, Kuwait, France, Switzerland, Portugal, and Spain. Most isolates belonged to phylogroups B2 (50%) and D (25%). An EC-B2 strain of clonal complex sequence type (ST) 131 was detected in all countries; other B2 isolates corresponded to ST28, ST405, ST354, and ST695 from specific areas. EC-D strains were clonally unrelated but isolates from 3 countries belonged to ST405. All CTX-M-15 plasmids corresponded to IncFII group with overrepresentation of 3 HpaI-digested plasmid DNA profiles (A, B and C; 85-120kb, similarity ≥70%). Plasmid A was detected in EC-B2 strains (ST131, ST354, or ST405), plasmid C was detected in B2 and D strains, and plasmid B was confined to worldwide-disseminated ST131. Most plasmids contained blaOXA-1, aac(6′)-Ib-cr, and blaTEM-1. Worldwide dissemination of CTX-M-15 seems to be determined by clonal complexes ST131 and ST405 and multidrug-resistant IncFII plasmids.