IncK Plasmid Encoding blaCTX-M-14 | CDC EID

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Volume 17, Number 4–April 2011
Research
Complete Sequence and Molecular Epidemiology of IncK Epidemic Plasmid Encoding blaCTX-M-14
Jennifer L. Cottell, Mark A. Webber, Nick G. Coldham, Dafydd L. Taylor, Anna M. Cerdeño-Tárraga, Heidi Hauser, Nicholas R. Thomson, Martin J. Woodward, and Laura J.V. Piddock

Author affiliations: The University of Birmingham, Birmingham, UK (J.L. Cottell, M.A. Webber, D.L. Taylor, L.J.V. Piddock); Veterinary Laboratories Agency, New Haw, Surrey, UK (N.G. Coldham, M.J. Woodward); European Nucleotide Archive–European Bioinformatics Institute, Hinxton, UK (A.M. Cerdeño-Tárraga); and The Wellcome Trust Sanger Institute, Hinxton (H. Hauser, N.R. Thomson)

Suggested citation for this article

Abstract
Antimicrobial drug resistance is a global challenge for the 21st century with the emergence of resistant bacterial strains worldwide. Transferable resistance to β-lactam antimicrobial drugs, mediated by production of extended-spectrum β-lactamases (ESBLs), is of particular concern. In 2004, an ESBL-carrying IncK plasmid (pCT) was isolated from cattle in the United Kingdom. The sequence was a 93,629-bp plasmid encoding a single antimicrobial drug resistance gene, blaCTX-M-14. From this information, PCRs identifying novel features of pCT were designed and applied to isolates from several countries, showing that the plasmid has disseminated worldwide in bacteria from humans and animals. Complete DNA sequences can be used as a platform to develop rapid epidemiologic tools to identify and trace the spread of plasmids in clinically relevant pathogens, thus facilitating a better understanding of their distribution and ability to transfer between bacteria of humans and animals.

Bacterial plasmids are key vectors of horizontal gene transfer, mediating the mobilization of genetic material from 1 bacterium to another. Their ability to capture DNA and to spread within and between bacterial species by conjugation facilitates the rapid dissemination of potentially beneficial genes through a bacterial population. These genes might alter virulence of the host, confer metabolic benefits, or enable the bacteria to colonize new environments (1). Genes that confer resistance to antimicrobial drugs used in human or veterinary medicine are often mobilized on plasmids. One class of resistance genes encode extended-spectrum β-lactamases (ESBLs), which confer resistance against many β-lactam antimicrobial drugs, leading to treatment failures (2). Within the past decade, cefotaximase-modifying (CTX-M) β-lactamases (CTX-M) have become the most prevalent ESBLs in bacteria isolated throughout the world in hospital and community settings (3). More than 85 variants have been identified (www.lahey.org/Studies), mainly in isolates of Escherichia coli that cause community-acquired urinary tract infections (4). Although clonal expansion events appear to have contributed to the spread of particular CTX-M variants, such as blaCTX-M-15 within E. coli strain O25:H4-ST131:05 (5,6), plasmids with the ability to spread efficiently, or epidemic plasmids, also are believed to be responsible for disseminating CTX-M ESBLs (7). The ability and frequency with which antimicrobial resistance genes disseminate between bacteria in humans, the environment, and animals is still debated, and the role of plasmids in this movement between ecosystems, including the food chain, is also still contested, despite mounting evidence that it occurs (8,9).

CTX-M-14 is the second most frequently identified CTX-M enzyme worldwide (10), detected in bacteria isolated from humans, animals, and the environment. CTX-M-14–producing strains show a high level of clonal diversity (11,12); therefore, dissemination has been attributed to conjugative plasmids rather than to clonal expansion of a bacterial host strain (13). In Europe, an association has been suggested between blaCTX-M-14 and plasmids of the incompatibility group IncK, or the spread of 1 particular IncK plasmid (11,13,14). In the United Kingdom in 2006, Liebana et al. described an ESBL-producing isolate from calves with diarrhea that carried blaCTX-M-14 on an IncK plasmid, denoted pCT (15,16). The plasmid spread to unrelated E. coli isolates within an index cattle farm and persisted within the environment. In this study, we report the full sequence and analysis of pCT and demonstrate the spread of pCT-like plasmids in animal and human E. coli isolates from the United Kingdom, Europe, Australia, and Asia.

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IncK Plasmid Encoding blaCTX-M-14 | CDC EID



Suggested Citation for this Article
Cottell JL, Webber MA, Coldham NG, Taylor DL, Cerdeño-Tárraga AM, Hauser H, et al. Complete sequence and molecular epidemiology of Inck epidemic plasmid encoding blaCTX-M-14. Emerg Infect Dis [serial on the Internet]. 2011 Apr [date cited].
http://www.cdc.gov/EID/content/17/4/645.htm


DOI: 10.3201/eid1704.101009


Comments to the Authors
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Laura J.V. Piddock, School of Immunity and Infection, The College of Medical and Dental Sciences, The University of Birmingham, Birmingham B15 2TT, UK; email: l.j.v.piddock@bham.ac.uk