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Molecular characterization of CTX-M-15-producing clinical isolates of Escherichia coli reveals the spread of multidrug-resistant ST131 (O25:H4) and ST964 (O102:H6) strains in Norway

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Naseer U, Haldorsen B, Tofteland S, Hegstad K, Scheutz F, Simonsen GS, Sundsfjord A and The Norwegian ESBL Study Group. Molecular characterization of CTX-M-15-producing clinical isolates of Escherichia coli reveals the spread of multidrug-resistant ST131 (O25:H4) and ST964 (O102:H6) strains in Norway. APMIS 2009; 117: 526–36.

Nationwide, CTX-M-producing clinical Escherichia coli isolates from the Norwegian ESBL study in 2003 (n=45) were characterized on strain and plasmid levels. BlaCTX-M allele typing, characterization of the genetic environment, phylogenetic groups, pulsed field gel electrophoresis (PFGE), serotyping and multilocus sequence typing were performed. Plasmid analysis included S1-nuclease-PFGE, polymerase chain reaction-based replicon typing, plasmid transfer and multidrug resistance profiling. BlaCTX-M-15 (n=23; 51%) and blaCTX-M-14 (n=11; 24%) were the major alleles of which 18 (78%) and 6 (55%), respectively, were linked to ISEcp1. Thirty-two isolates were of phylogenetic groups B2 and D. Isolates were of 29 different XbaI-PFGE-types including six regional clusters. Twenty-three different O:H serotypes were found, dominated by O25:H4 (n=9, 20%) and O102:H6 (n=9, 20%). Nineteen different STs were identified, where ST131 (n=9, 20%) and ST964 (n=7, 16%) were dominant. BlaCTX-M was found on ≥100 kb plasmids (39/45) of 10 different replicons dominated by IncFII (n=39, 87%), FIB (n=20, 44%) and FIA (n=19, 42%). Thirty-nine isolates (87%) displayed co-resistance to other classes of antibiotics. A transferable CTX-M phenotype was observed in 9/14 isolates. This study reveals that the majority of CTX-M-15-expressing strains in Norway are part of the global spread of multidrug-resistant ST131 and ST-complex 405, associated with ISEcp1 on transferrable IncFII plasmids.
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Keywords: CTX-M-15; ESBL; MDR; PBRT; ST131

Document Type: Research Article

Affiliations: 1: Reference Centre for Detection of Antimicrobial Resistance (K-res), Department of Microbiology and Infection Control, University Hospital of North-Norway, Tromsø; 2: The International Escherichia and Klebsiella Centre (WHO), Statens Serum Institut, Copenhagen, Denmark; and

Publication date: 2009-07-01

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