Transmission of plasmid-borne and chromosomal blaCTX-M-64 among Escherichia coli and Salmonella isolates from food-producing animals via ISEcp1-mediated transposition

Qiu-Yun Zhao, Pin-Xian Chen, Ling Yang, Run-Mao Cai, Jia-Hang Zhu, Liang-Xing Fang, Mark A Webber, Hong-Xia Jiang

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Objectives: To clarify the transmission mechanism of the blaCTX-M-64 gene between Escherichia coli and Salmonella isolates from food animals. Methods: A total of 329 E. coli and 60 Salmonella isolates collected from food animals in 2016 were screened for the presence of blaCTX-M-64 genes. The blaCTX-M-64-positive isolates were typed and plasmid and chromosome DNA was sequenced to determine the genetic context of blaCTX-M-64 and the plasmid types present. Results: The blaCTX-M-64 gene was identified in only three E. coli isolates but was the predominant gene in the Salmonella isolates (n = 9). These 12 CTX-M-64-positive isolates were all resistant to ampicillin, cefotaxime, ceftiofur, ceftriaxone, ceftazidime and florfenicol and 9 were resistant to ciprofloxacin. The blaCTX-M-64 gene was located on transferable IncI2 plasmids and an IncHI2 plasmid in three E. coli and one Salmonella isolate, respectively. The remaining eight Salmonella isolates contained blaCTX-M-64 integrated into the chromosome. Different genetic contexts of blaCTX-M-64 genes were found among the 12 isolates: ISEcp1-blaCTX-M-64-orf477-A/C on IncI2 plasmids of 3 E. coli isolates; DISEcp1-blaCTX-M-64-orf477-A/C in the chromosome of 1 Salmonella isolate; and ISEcp1-blaCTX-M-64-orf477 on the IncHI2 plasmid and chromosome of 8 Salmonella isolates. Conclusions: To the best of our knowledge, this is the first report of chromosomally encoded CTX-M-64 in Salmonella isolates. ISEcp1-mediated transposition is likely to be responsible for the spread of blaCTX-M-64 between different plasmids and chromosomes in Enterobacteriaceae especially E. coli and Salmonella.

Original languageEnglish
Pages (from-to)1424–1427
Number of pages4
JournalJournal of Antimicrobial Chemotherapy
Issue number6
Early online date28 Feb 2020
Publication statusPublished - Jun 2020

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