Chromosomal locations of mcr-1 and [bla.sub.CTX-M-15] in fluoroquinolone- resistant Escherichia coli ST410

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From: Emerging Infectious Diseases(Vol. 22, Issue 9)
Publisher: U.S. National Center for Infectious Diseases
Document Type: Letter to the editor
Length: 1,438 words
Lexile Measure: 1460L

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To the Editor: Recently, Yi-Yun Liu et al. reported on the discovery of mcr-1, a plasmidborne resistance gene mediating resistance to colistin, in isolates obtained from humans and animals (1). Since the original publication, mcr-1 with or without the insertion element ISAp11 has been detected on plasmids of different incompatibility groups, including IncI2, IncHI2, and IncX4, and in many different countries (1-3). Because colistin is a last-resort parenteral antimicrobial drug, the transfer of mcr-1 by conjugation or through mobilizable plasmids raises concern about the emergence of pan-resistant Enterobacteriaceae.

We previously described extended-spectrum [beta]-lactamase (ESBL)-producing and carbapenemase-producing isolates obtained from livestock and a human in Germany that harbored the mcr-1 gene (2). Because the transfer of mcr-1 through the food chain is highly likely, we looked for its presence in 62 whole-genome sequenced ESBL-producing Escherichia coli isolates obtained during 2012-2013 from food products sampled in Germany (online Technical Appendix, http://wwwnc.cdc.gov/EID/article/22/8/160692-Techapp1.pdf). We detected 4 isolates harboring the mcr-1 gene (E. coli RL138, RL145, RL158, and RL465) that displayed a colistin MIC of 4 mg/L (online Technical Appendix Table 1). The raw sequencing reads and the assembled contigs of the mcr-1 -positive isolates were deposited in the European Nucleotide Archive under project accession no. PRJEB13470. We conducted conjugation experiments to analyze the transferability of mcr-1 (online Technical Appendix). For all isolates except RL465, mcr1 was transferable to E. coli J53 Azr. For isolates RL138, RL145, and RL158, the mcr-1 gene was present on IncX4 and IncHI2 plasmids (Figure, panel A, http://wwwnc.cdc. gov/EID/article/22/8/16-0692-FLhtm; online Technical Appendix Table 2). The sequence type (ST) 410 E. coli isolate RL465 was detected in a turkey hen meat sample from 2013 and harbored blaCTX-M-15 and mcr-1, a gene combination hitherto identified only in travelers from the Netherlands and children from China (4). Both the [bla.sub.CTX-M-15] and mcr-1 genes were not transferable, indicating that neither gene was plasmid-encoded. Examination of the genetic environment of mcr-1 in the assembled gapped genome showed a chromosomal location for the mcr-1 transposition unit that included an ISApl1 element (Figure 1, panel A; online Technical Appendix Figure 1, panel A) flanked by the inverted repeats (IR-R1, IR-R2, and IR-L1). We verified the chromosomal...

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Gale Document Number: GALE|A464046000